Power Network Application Trainer
MI 3298
Instruction manual
with exercises
Ver. 1.0.1, Code no. 20 752 871
Power Network Application Trainer Introduction MI 3298
Mark on your equipment certifies that it meets European Union requirements for
EMC, LVD, ROHS regulations
Distributor:
Manufacturer:
Metrel d.d.
Ljubljanska cesta 77
SI-1354 Horjul
E-mail: metrel@metrel.si
http://www.metrel.si
© 2018 METREL Electrical power installations – testing and verifications, METREL,
2018
No part of this publication may be reproduced or utilized in any form or by any means
without permission in writing from METREL.
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Power Network Application Trainer Introduction MI 3298
TABLE OF CONTENTS:
Introduction .................................................................................................................... 4
Earth / Ground network impedance analysing .......................................................... 36
Power generators, transformers, coils .................................................................... 162
Insulating material analyses ..................................................................................... 191
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Power Network Application Trainer Introduction MI 3298
Introduction
1 Introduction ................................ ................................ ................................ ........ 9
1.1 Metrel Academy ...................................................................................................... 9
1.2 Training Modules ..................................................................................................... 9
1.3 Knowledge base .....................................................................................................11
1.4 Partnership .............................................................................................................11
1.5 References .............................................................................................................11
1.6 Certified training modules .......................................................................................12
1.6.1 Module packages ............................................................................................12
1.6.2 Wall Posters ................................ ................................................................ ....12
1.6.3 Scope of Application & Technical Support .......................................................12
1.6.4 Qualification certificate ....................................................................................12
1.7 Description of HV training modules ........................................................................13
1.8 Description of MI 3298 HV Training Module set’s ...................................................15
1.8.1 Markings on the module set’s ..........................................................................15
1.8.2 MI 3298 P1: Transmission Line with Pylon1 ....................................................16
1.8.2.1 MI 3298 P1: Technical specification .............................................................19
1.8.2.2 MI 3298 P1 Training Module ........................................................................23
1.8.2.3 MI 3298 P1 - Warnings and safe rules .........................................................24
1.8.3 MI 3298 T: Power Transformer, Cables and Power Loads ..............................25
1.8.3.1.1 MI 3298 – T: Technical specification ........................................................28
1.8.3.2 MI 3298 T Training Module ..........................................................................29
1.8.3.3 MI 3298 T - Warnings and safe rules: ..........................................................30
1.9 Test methods .........................................................................................................31
1.9.1 Auto sequence® ..............................................................................................32
1.9.1.1 Auto Sequence® groups menu ....................................................................32
1.10 Safety precautions..................................................................................................33
1.10.1 Station ground tests ........................................................................................33
1.10.2 Surge arrester ground test...............................................................................33
1.10.3 Neutral and shield wire ground tests appropriate work procedures ..................34
1.10.4 Equipment neutral ground test precautions .....................................................34
1.11 Warnings ................................................................................................................34
1.11.1 Inspectors guide – safety precautions before test ............................................34
1.11.2 Inspectors guide – safety hazards during test..................................................34
1.11.3 Inspectors guide – after test reminder .............................................................35
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Power Network Application Trainer Introduction MI 3298
Figure 1-1: Organizations included in certification ................................................................................ 10
Figure 2-1: Training module road map .................................................................................................. 10
Figure 3-1: HV Training Module trainer concept ................................................................................... 14
Figure 4-1: MI 3298 P1 training module ................................................................................................ 16
Figure 5-1: Pylon foot default numbering .............................................................................................. 17
Figure 6-1: Pylon foots grounding simulation ........................................................................................ 17
Figure 7-1: Pylon impedance type simulation ....................................................................................... 18
Figure 8-1: List of measurements available with MI 3290 and MI 3295M ............................................. 18
Figure 9-1: List of measurements available with MI 3295S and MI 3295M .......................................... 19
Figure 10-1: MI 3298 P1 resistance test between selected terminals................................................... 19
Figure 11-1: MI 3298 P1 resistance test between selected terminals................................................... 20
Figure 12-1: MI 3298 P1 resistance test between selected terminals................................................... 20
Figure 13-1: MI 3298 P1 resistance test between selected terminals................................................... 21
Figure 14-1: MI 3298 P1 resistance test between selected terminals................................................... 22
Figure 15-1: MI 3298 P1 standard set ................................................................................................... 23
Figure 16-1: MI 3298 T “puzzle” training module .................................................................................. 25
Figure 17-1: Simulation of different transformer winding conditions ..................................................... 26
Figure 18-1: List of measurements available on MI 3280 ..................................................................... 26
Figure 19-1: List of measurements available on Metrel Insulation testers ............................................ 27
Figure 20-1: “Inductive” measurements mode available on MI 3250 instrument .................................. 27
Figure 21-1: MI 3298 T standard set ..................................................................................................... 29
Figure 22-1: Example of Auto Sequences under IEEE 81 -2012 Auto sequence ................................. 33
Figure 23-1: Set of Metrel measuring instruments, which could be used with MI 3298 P1 .................. 36
Figure 24-2: Presentation of specific earth resistance .......................................................................... 44
Figure 25-2: Specific resistance measurement: probe distance vs depth of measurement ................ 45
Figure 26-2: Wenner method for specific earth resistance measurements .......................................... 46
Figure 27-2: Schlumberger method for specific earth resistance measurements ................................. 46
Figure 28-2: Placement of measuring probes (62% method) ............................................................... 48
Figure 29-2: Definition of parameter “a” ............................................................................................... 49
Figure 30-2: Straight-line measuring probes placement ....................................................................... 49
Figure 31-2: Equilateral placement ....................................................................................................... 51
Figure 32-3: Different measured voltage drops at low and high probe resistance ................................ 52
Figure 33-2: MI 3290 – Earth Analyser and MI 3295S–Step Contact Voltage Measuring System ....... 53
Figure 34-2:MI 3123 - Hand-held installation Smartec Earth / Clamptester ......................................... 53
Figure 35-2: 2 – pole measurement ...................................................................................................... 57
Figure 36-2: 3 – pole measurement ...................................................................................................... 58
Figure 37-2: 4 – pole measurement ...................................................................................................... 58
Figure 38-2: Selective (Iron Clamp) measurement ............................................................................... 59
Figure 39-2: 2 Clamps measurement .................................................................................................... 60
Figure 40-2: HF-Earth Resistance (25 kHz) measurement ................................................................... 60
Figure 41-2: Compensation of inductive component with HF 25 kHz method ...................................... 61
Figure 42-2: Selective (Flex Clamps 1-4) measurement ....................................................................... 61
Figure 43-2: Passive (Flex Clamps) measurement ............................................................................... 62
Figure 44-2: Substitute circuit for Passive (Flex Clamps) measurement .............................................. 63
Figure 45-2: Pylon Ground Wire Test (PGWT) example ....................................................................... 64
Figure 46-2: Impulse Measurement example ........................................................................................ 66
Figure 47-2: Typical Impulse shape short-circuit ................................................................................... 66
Figure 48-2: Influence of inductive impedance part at impulse measurement ...................................... 67
Figure 49-2: Influence of inductive impedance part at 3-pole measurement ........................................ 68
Figure 50-2: Dangerous voltages on a faulty earthing system .............................................................. 69
Figure 51-2: Example of ground potential measurement ...................................................................... 71
Figure 52-2: Potential gradient measurements example (straight line)................................................. 71
Figure 53-2: Test step/contact voltage plates and 25kg probes ........................................................... 73
Figure 54-2: Step voltage measurement with MI3290 instrument ......................................................... 73
Figure 55-2: Step voltage measurement with MI3295S & MI3295M instruments ................................. 74
Figure 56-2: Contact voltage measurement with MI3290 instrument.................................................... 74
Figure 57-2: Contact voltage measurement with MI3295S & MI3295M instruments ............................ 74
Figure 58-2: Set of Metrel instruments used with MI 3298 P1 training module .................................... 75
Figure 59-2: Available measurement on the MI 3290 Earth Analayser................................................. 75
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Power Network Application Trainer Introduction MI 3298
Figure 60-2: 3-pole earth resistance measurement with MI 3290 ......................................................... 81
Figure 61-2: 4-pole earth resistance measurement with MI 3290 ......................................................... 84
Figure 62-2: Earth measurement with MI 3123 ..................................................................................... 87
Figure 63-2: Earth measurement with MI 3295S................................................................................... 89
Figure 64-2: 4-pole earth measurements setup with MI 3290 ............................................................... 92
Figure 65-2: 4-pole earth measurements setup with MI 3290 ............................................................... 94
Figure 66-2: 4-pole earth measurements setup with MI 3290 ............................................................... 95
Figure 67-2: S-Flex measurement setup with MI 3290 ......................................................................... 98
Figure 68-2: S-Flex measurement setup with MI 3290 ....................................................................... 101
Figure 69-2:S-Flex measurement setup .............................................................................................. 104
Figure 70-2: S-Flex measurement setup ............................................................................................. 106
Figure 71-2: S-Flex measurement setup for measuring two pylon foot’s ............................................ 109
Figure 72-2: S-Flex measurement setup for measuring all pylon foots............................................... 111
Figure 73-2: PGWT measurement setup ............................................................................................ 113
Figure 74-2: PGWT measurement setup with connected ground wire ............................................... 115
Figure 75-2: HF measuring method setup ........................................................................................... 117
Figure 76-2: Example of Auto Sequence window ............................................................................... 120
Figure 77-2: 4-pole and S-Flex measurement setup ........................................................................... 121
Figure 78-2: Auto sequence setup (4-pole and S-Flex) ...................................................................... 122
Figure 79-2: 4-pole, HF and S-Flex measurement setup .................................................................... 125
Figure 80-2: Auto sequence setup (4-pole, HF and S-Flex) ............................................................... 126
Figure 81-2: Impulse measuring method setup ................................................................................... 131
Figure 82-2: Impulse measuring method setup with GW conenction.................................................. 133
Figure 83-2: Step voltage setup with MI 3290 ..................................................................................... 136
Figure 84-2: Step voltage setup with MI 3295S .................................................................................. 139
Figure 85-2: Contact (Touch) voltage setup with MI 3290 .................................................................. 142
Figure 86-2: Contact (Touch) voltage setup with MI 3295S ................................................................ 145
Figure 87-2: GPR measuring method with MI 3290 ............................................................................ 149
Figure 88-2: Test point selection for GPR measurement .................................................................... 150
Figure 89-2: GPR measuring method with MI 3290 & MI 3295M ....................................................... 153
Figure 90-2: Selection of test point for GPR measurements ............................................................... 154
Figure 91-2: Graphical presentation of GPR measurements .............................................................. 157
Figure 92-2: GPR measurement with MI 3290 .................................................................................... 158
Figure 93-2: Graphical presentation of GPR measurements .............................................................. 161
Figure 94-3: Set of Metrel measuring instruments, which could be used with MI 3298 T................... 162
Figure 95-3: Single-phase VT/PT transformer and CT transformer turn ratio
measurement connection ................................................................................................ 167
Figure 96-3: Turn ratio measurement of three-phase transformer ...................................................... 169
Figure 97-3: Winding resistance measurement of single-phase transformer ..................................... 170
Figure 98-3: Winding resistance measurement of three-phase transformer ....................................... 171
Figure 99-3: MI 3298 T training module .............................................................................................. 172
Figure 100-3: Transformer turn ratio measurement setup with MI 3280 ............................................. 177
Figure 101-3: Proper crocodiles mounting to ensure good contact .................................................... 180
Figure 102-3: Winding resistance measurement setup with MI 3280 ................................................. 184
Figure 103-3: Winding resistance measurement setup with MI 3250 ................................................ 187
Figure 104-3: Winding resistance measurement setup with MI 3250 ................................................ 189
Figure 105-3: Metrel measuring instruments for insulation measurement, which could be used
with MI 3298 T .............................................................................................................. 191
Figure 106-3: Insulation resistance and capacitance model, partial and total currents ...................... 194
Figure 107-3: Typical current / time diagram for a real voltage source ............................................... 195
Figure 108-3: Current diagram for an ideal voltage source ................................................................. 195
Figure 109-3: Typical insulation resistance/time diagram for a spot reading test ............................... 197
Figure 110-3: Time diagrams of good and bad insulation tested with the time-rise method .............. 198
Figure 111-3: The current/time diagram of a good and bad insulation tested with dielectric
discharge method ......................................................................................................... 199
Figure 112-3: Typical measuring procedure for step voltage measurement ....................................... 200
Figure 113-3: Typical step voltage measurement results ................................................................... 200
Figure 114-3: Measuring procedure for withstanding voltage measurement. ..................................... 201
Figure 115-3: Maximum safe capacitance of tested insulation versus test voltage ............................ 204
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Power Network Application Trainer Introduction MI 3298
Figure 116-3: Discharging of insulating material (Ciso = 100 nF, Utest = 5 kV) ................................. 204
Figure 117-3: MI 3298 T training module for insulation testing ........................................................... 205
Figure 118-3: Measurement setup for insulation testing ..................................................................... 208
Figure 119-3: Diagnostic test measurement setup ............................................................................. 212
Figure 120-3: Step voltage test measuring setup................................................................................ 215
Figure 121-3: Transformer insulation resistance measurement setup (primary– secondary side) ..... 217
Figure 122-3: Transformer Insulation resistance test setup (primary side – pe terminal) ................... 221
Figure 123-3: Transformer Insulation resistance test setup (secondary side – pe terminal) .............. 223
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Power Network Application Trainer Introduction MI 3298
Table 1-1: Resistance measurements on the MI 3298 P1 module between selected terminals…… 19
Table 2-1: Resistance measurements on the MI 3298 P1 module between selected terminals .......... 20
Table 3-1: Resistance measurements on the MI 3298 P1 module between selected terminals .......... 21
Table 4-1: Resistance measurements on the MI 3298 P1 module between selected terminals .......... 21
Table 5-1: Resistance measurements on the MI 3298 P1 module between selected terminals .......... 22
Table 6-1: Turn ratio related to the switch position ............................................................................... 28
Table 7-1: Resistance of primary windings U, V, W related to the switch position ............................... 28
Table 8-1: Technical data of the” HV box” intended for insulation test training .................................... 28
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Power Network Application Trainer Introduction MI 3298
1 Introduction
The purpose of this book is to introduce the reader with main topics on high voltage
(power) testing, both in theory as well as in practice. As the book contains hands-on
exercises, it is especially suited for institutions which also wish to share the
knowledge further:
Institutes,
Training centres,
Associations,
Electrical Safety Boards,
Trainers for high voltage (power) environment,
- Transformers & substations,
- Power networks & distributions & transmission,
Registered training groups.
1.1 Metrel Academy
Seminars and practical trainings are prepared by Metrel as a package through the
Power Training Modules under the Metrel Academy.
All training modules are registered by the Ministry of Infrastructure (Energy
Directorate) in Slovenia. It is also possible to register a training module through a
national or an international institute or other partners (Institutes, Training centres,
Electricity Safety Boards, Trainers for Power environment).
All training modules should be equipped with:
A Catalogue of Knowledge,
A Catalogue of Exam,
A Certificate for supplementary qualification and competences.
Certified Training Modules and Seminars are supported by the Metrel Academy.
Within the Knowledge section we make recommendations and suggestions in
support of national vocational qualification schemes. We can also offer training with
completely new Training Modules for any new application areas.
Registering of the module is possible:
Through national or international institute
Through the Ministry of Infrastructure (Energy Directorate) in Slovenia
Partner.
1.2 Training Modules
The purpose behind Metrel's MI 3298 HV Training Platform certifications:
Only trained personnel can achieve the competency to work as a professional
in an environment of HV platforms and surroundings.
National or international training module equipped with catalogue of
knowledge could be recognized as valuable for a particular field.
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Power Network Application Trainer Introduction MI 3298
Metrel is offering equipment, training sets and modules together with
knowledge and certificates.
Figure 1-1: Organizations included in certification
The whole package includes:
Knowledge Guideline Handbook Registered Training Program
Certified Training Test Equipment Safety Precautions on Screen
“Module Puzzle’s”
Figure 2-1: Training module road map
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Power Network Application Trainer Introduction MI 3298
1.3 Knowledge base
Metrel is continuously investing in research and development, which leads to new
advanced product solutions and improved technical and application knowledge and
practice. Our design & development engineers and product managers have
thoroughly developed their technical knowledge and application experience about
different markets and application fields, so we can proudly state that we are experts
in our field. Metrel works in co-operation with several important external organizations
and institutions like:
IEC Technical Committees and their Working Groups
Different Universities and Institutes
Electro-technical Associations
Engineers Associations
Electrical Safety Boards
Chambers of Engineers
Chambers of Commerce and Industry
Chambers of Craft and Small Business
1.4 Partnership
Metrel is a member of the Slovenian Institute for Standardization and cooperates
closely with important associations and committees related to its industry sectors. We
have experts actively participating in several technical committees on the national as
well as international base (IEC Technical Committees and Working Groups). Metrel is
also involved in the Committee for the Electro-Technical Safety and Low-voltage
electrical installations (NNELI) as a partner company through »eTest scheme« in
Slovenia. We are a partner company of E-Check Association of electrical installers in
Germany and cooperate with similar associations in other countries.
1.5 References
Through our own participation in providing and supporting national vocational
qualification programs in the field of electrical safety during past decades and
through our close collaboration with professionals from various industries, at Metrel
Academy we are aware of the importance to continuously develop knowledge and
new skills through various levels of training and qualification programs. This ensures
self-confidence of the workforce in companies involved with Electrical Safety; it
boosts their competitiveness and enables safe and profitable working processes of
their customers.
Metrel’s participation in preparation of curricula for electrical engineering in Slovenia
includes the following:
Preparation of the Knowledge and Skills catalogue.
Giving assistance in defining qualification requirements list for the candidates
in the vocational qualification program.
Preparation of the Assessment Exams catalogue.
Metrel also assists experts working on the vocational qualification programs through
its distribution – partners’ network worldwide. This has been mostly related to the
application of Metrel test and measurement instruments.
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Power Network Application Trainer Introduction MI 3298
1.6 Certified training modules
Certified Training Modules and Seminars are supported with packages of printed
Handbooks, White paper, Application Notes, Exercises, Quick Guide Charts, and
Posters together with other elements of Application and Technical Support. All Power
voltage training modules can be performed on Metrel's Power application trainer.
1.6.1 Module packages
E-Handbooks, Quick Guide Charts, Application Notes and Exercises about
measuring and testing based on the International / European Standardization for
every participant.
1.6.2 Wall Posters
Wall posters visually represent typical testing and measurement procedures and / or
troubleshooting tasks, or a list of required customized tests in certain areas of
application.
1.6.3 Scope of Application & Technical Support
Demonstration Equipment.
Testing instruments.
Power Point Presentations on product solutions.
On-line Technical Support: any inquires related to Metrel products can be sent
on the following addresses:
o help@metrel.si
o info@metrel.co.uk
o metrel@metrel.de
Bespoke product training for an individual customer or larger groups of people.
Complete distributor set-up training (product, repair, and calibration training).
B2B web support provides specific technical information for Metrel partners.
Download centre enables you downloading product technical data (Manuals,
Datasheets, PC Software, Presentations etc).
1.6.4 Qualification certificate
European Qualification Certificate adjusted to the EU-countries industry standards
ensures the competency of individual participants who pass the final Exam on
Theoretical and Practical knowledge for the specific locally approved Training
Module:
Know-How Package – for a Transparent Localization Process.
Knowledge Catalogue – for the specific Training Module for modification to a
local – National regulation.
Exam’s Catalogue – with the definition of the minimum level of the Entry
conditions for a participant.
Approved Certificate – approval of the obtained qualification when signed by
a local authorized organization like:
o Training organization.
o Electrical Safety Board Organization, as for example NNELI eTest /
local – National AIE partner.
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Power Network Application Trainer Introduction MI 3298
Metrel Academy has put out a comprehensive list of training sessions in order to
help you master the latest measurement and testing technologies.
1.7 Description of HV training modules
MI 3298HV Training Module is a multipurpose trainer facility platform suited for
middle level technical schools, training centres and independent organizations who
wish to evaluate people’s competency and improve practical and theoretical
knowledge of their listeners. The MI 3298 is ideally suited for training and education
of larger groups of people as well as for independent practice.
The MI 3298 HV Training Module ensures absolute safety for the user. The user
should follow instructions for safety work with instrument.
Simulation of possible errors is bringing the know-how about troubleshooting,
maintaining and caring out different measurements on the real field. It is aimed as
well to be used at sale-demonstration for presentation of different measurements
techniques.
Note:
When using training modules in technical schools, we suggest the presence of a
qualified person during the practice.
Applications:
Education, trainings and seminars with theoretical and practical exercising and
testing for upgrading knowledge of a professional’s competence.
Education and practical training of electrical contractors about safety procedures,
measuring methods and knowledge.
Demonstration on how to use different measurement instruments and testers.
MI 3298 HV Training Module supports simulation on:
Electrical Power Installations and HV and MV AC Power Substations.
Transmission Lines with Pylons, Lines and Cables.
Industrial platforms with Power Transformers and Power Loads.
Other insulated or interconnected systems of Rails, Pipes, Fences.
Switching installations and parallel Measuring systems.
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Power Network Application Trainer Introduction MI 3298
Figure 3-1: HV Training Module trainer concept
HV Training Modules
Measuring methods which could be simulated (trained):
Ground Networks Impedance
Earth Surface Potentials
Fault Simulated Step & Contact Voltage
Equipotential bonding & Connectivity
Pylon Selective legs
HF earth impedance
Cables Impedances, Resistances and Insulation
HV Insulation Analysis
Lightning Protection & Varistors and Surge protection
Fault Currents and Fuse Characteristics evaluation
Transformer’s Impedance
Winding resistance measurements
Transformers Turn Ratio Analysing
Different modules could be evaluated separately as an independent system and / or
connected together to express the interconnectivity problems and influences between
them.
This type of approach could give the trained personnel clear information on testing
methods, measured values and results on known systems and overview over
situations where systems are becoming more complex when connected together.
Check the general outlook of received training modules and their accessories. There
should be no broken, damaged or scratched parts and no other visible defects that
could lead to electric shock or other hazard when working with the module. Defective
parts should not be used and should be replaced.
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Power Network Application Trainer Introduction MI 3298
1.8 Description of MI 3298 HV Training Module set’s
1.8.1 Markings on the module set’s
The symbol on the HV training module means »Read the Instruction manual with
special care for safe operation«. The symbol requires an action!
If the HV training module is used in a manner not specified in this Instruction
manual, the protection provided by HV training module could be impaired!
Read this Instruction manual carefully, otherwise the use of the HV training
module may be dangerous for the operator, the test equipment itself or for the
tested object!
Do not use the HV training module if any damage is noticed!
Consider all generally known precautions in order to avoid risk of electric shock
while dealing with hazardous voltages!
Service intervention is only allowed to be carried out by competent authorized
personnel!
Do not use the HV training module in a wet environment, around explosive gas,
vapour or dust.
For the training purposes and for your safety, use Metrel instruments described in
this manual
The symbol on the HV training module means “Hazardous voltage may be
present at the test terminals!”.
Do not touch any conductive parts of HV training module under test during the
test, risk of electric shock!
Mark on your equipment certifies that it meets European Union requirements for
EMC, LVD, and ROHS regulations.
This equipment should be recycled as electronic waste.
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Power Network Application Trainer Introduction MI 3298
13
1.8.2 MI 3298 P1: Transmission Line with Pylon1
MI 3298 P1 main parts:
Figure 4-1: MI 3298 P1 training module
1. Connection point for H(C1) probe – earth resistance (impedance)
measurements - RCE
2. Pylon - connection point for E(C2), ES(P2) clamp
3. Simulating of ground wire connection
4. Selection switch - selection of different resistance pylon foots earthing
condition
5. Selection switch – selection of different earth character (resistive/inductive
type)
6. Connection for the next (neighbourhood) Training module (puzzle concept)
7. “Soil simulation – semi-conductive material” for GPR, step and contact voltage
measurements
8. Fuse 250V T1A
9. Connection point for S(P1) clamp for ground resistance measurement – RP
10. Ground terminal for the pylon
11. Connection point for H(C1) probe – GPR, Step & Contact measurement- RCS
12. Pylon grounding ring simulation
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Power Network Application Trainer Introduction MI 3298
Figure 5-1: Pylon foot default numbering
1- Pylon foot number 1
2- Pylon foot number 2
3- Pylon foot number 3
4- Pylon foot number 4
Explanation for selection switch Nm. 4– simulation of pylon fault earthing conditions
Figure 6-1: Pylon foots grounding simulation
Pos 0 – regular pylon foots condition (different earth resistance for each foot)
Pos 1 – broken earth connection for pylon foots 2 and 3
Pos 2– simulation of “earthing ring” connection – for GPR, Step & Contact
measurements
Pos 3 –broken pylon foots connection
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Power Network Application Trainer Introduction MI 3298
Explanation for selection switch Nm. 5 (Figure 7-1) – simulation of pylon character
type
Figure 7-1: Pylon impedance type simulation
List of measurements which could be done on MI 3298 – P1 module with MI 3290
Earth Analyser and MI 3295M Step Contact Meter:
Figure 8-1: List of measurements available with MI 3290 and MI 3295M
Visual check (Safety precautions Before, During and After tests)
Ground Networks Impedance,
Pylon ground impedance,
Pylon legs impedance with flex clamps,
HF resistance measurement,
Passive flex clamps measurement,
Impulse impedance measurement,
Pylon Ground Wire Test (PGWT)
Ground Potential Rise (GPR),
Earth Surface Potential,
Fault Simulated Step & Contact Voltage.
List of measurements which could be done on MI 3298 – P1 module with MI 3295S
Step Contact Voltage Measuring System and MI 3295M Step Contact Meter:
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Power Network Application Trainer Introduction MI 3298
Test terminal
Low limit [Ω]
High limit [Ω]
1
14,25
15,75
2
9,5
10,5 3 19
21
4
4,5
5,5 5 450
550
6
84,6
103,4
7
450
550
Figure 9-1: List of measurements available with MI 3295S and MI 3295M
Ground Potential Rise (GPR),
Earth Surface Potential,
Fault Simulated Step & Contact Voltage.
1.8.2.1 MI 3298 P1: Technical specification
1. Resistance between “Earth” terminal and accessible test terminals –
Figure 10-1: MI 3298 P1 resistance test between selected terminals
Table 1-1: Resistance measurements on the MI 3298 P1 module between selected terminals
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Power Network Application Trainer Introduction MI 3298
Position of Switch 5
Low limit [Ω]
High limit [Ω]
1
2,16
2,64
2
2,40
3,20
2. Resistance between “Earth” terminal and “pylon foots”–
Figure 11-1: MI 3298 P1 resistance test between selected terminals
Table 2-1: Resistance measurements on the MI 3298 P1 module between selected terminals
3. Resistance between “Earth” terminal and “pylon foots” terminals –
Figure 12-1: MI 3298 P1 resistance test between selected terminals
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Power Network Application Trainer Introduction MI 3298
Test terminal
Low limit [Ω]
High limit [Ω]
1
14,25
15,75
2
0.L
0.L 3 0.L
0.L 4 4,5
5,5
Test terminal
Low limit [Ω]
High limit [Ω]
1
4,5
5,5 2 4,5
5,5 3 4,5
5,5 4 4,5
5,5
Table 3-1: Resistance measurements on the MI 3298 P1 module between selected terminals
4. Resistance between “Earth” terminal and “pylon foots” terminals –
Figure 13-1: MI 3298 P1 resistance test between selected terminals
Table 4-1: Resistance measurements on the MI 3298 P1 module between selected terminals
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Power Network Application Trainer Introduction MI 3298
Test terminal
Low limit [Ω]
High limit [Ω]
1
0.L
0.L
2
0.L
0.L
3
0.L
0.L
4
4,75 kΩ
5,25 kΩ
5. Resistance between “Earth” terminal and “pylon foots” terminals –
Figure 14-1: MI 3298 P1 resistance test between selected terminals
Table 5-1: Resistance measurements on the MI 3298 P1 module between selected terminals
General data:
Dimesnions (w x h x d)..................40 cm x 11cm x 33 cm
Pollution degree............................2
Weight...........................................3,94 kg
Degree of protection ...................... IP 40
Operation conditions:
Working temperature range ......... -10°C ... 50°C
Maximum relative humidity .......... 90 %RH (0°C ... 40 °C), non-condensing
Working nominal altitude.............. up to 3000 m
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Power Network Application Trainer Introduction MI 3298
1.8.2.2 MI 3298 P1 Training Module
Upon receipt of Demonstration board, it is advisable to check the content of the
delivery. The following items have to be included:
- MI 3298 P1 Training Module, code 20 919 237
- 2 step voltage probes, code 20 052 009
- Pylon, code 20 052 006
- Ground wire connection, code 20 692 042
- Puzzle interconnection part, code 20 052 010
- Set of measuring cables:
Coax measurement cable (black), code 20 692 124
Measurement cable (red), code 20 691921
Measurement cable (blue), code 20 691923
Measurement cable (green), code 20 691924
- Flex current clamps A 1612 (phi 14 cm), code 20 051 222, 1 pcs
Optional: Flex current clamps A 1612 (phi 14 cm), code 20 051 222, 3 pcs
Figure 15-1: MI 3298 P1 standard set
23
Power Network Application Trainer Introduction MI 3298
In case of any module malfunction or any damage notice, the module must be
serviced by a competent service department. Contact your dealer or producer for
further information.
Producer’s contact details:
Address: METREL d.d.
Ljubljanska 77
SI-1354 Horjul
Slovenia, Europe
Tel.: +386 1 755 82 00
Fax.: +386 1 754 92 26
URL: http://www.metrel.si
E-mail: metrel@metrel.si
Use a soft patch slightly moistened with water or alcohol to clean the surface of the
HV Application trainer and leave it to dry totally before use.
Do not use liquids based on petrol!
Do not spill cleaning liquid over the demo board!
1.8.2.3 MI 3298 P1 - Warnings and safe rules
Note:
Follow the instructions for safety work!
Warnings:
Never touch test terminals during the measurements!
Connect instrument according the instructions described in this manual.
For the training purposes and for your safety, use Metrel instruments
described in this manual
Do not connect higher voltage than 55 Vac CAT 0 between RCE/RCS and pylon.
For other test terminals use max 40 Vac CAT 0 with limited output power 2 W.
Do not apply voltage to “Soil simulation – semi-conductive material” for GPR,
step and contact voltage measurements.
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Power Network Application Trainer Introduction MI 3298
1.8.3 MI 3298 T: Power Transformer, Cables and Power Loads
MI 3298 T main parts:
Figure 16-1: MI 3298 T “puzzle” training module
List of main elements:
1. Transformer connection terminals and its technical data
Voltage ratio: 10075 V / 1000 V
Vector group: Yyn0
Note: For measuring the transformer isolation use max. test voltage
1kV!
2. Test point for cable insulation resistance testing. Max. test voltage 5 kV DC!
3. Tube Fuse 250V T1A
4. Switch for selecting different transformer winding conditions
5. Ground terminal
6. Connection for the next (neighbourhood) training module (puzzle concept)
25
Power Network Application Trainer Introduction MI 3298
Figure 17-1: Simulation of different transformer winding conditions
1 – Regular “Power transformer winding condition”
2 – Simulated partial shortcut on winding u and broken connection on winding w
3 – Broken connection on winding w
List of measurements and instruments, which could be done with MI 3298 T module
with MI 3280 instrument:
Figure 18-1: List of measurements available on MI 3280
Visual check (Safety precautions Before, During and After tests)
Transformer’s Turn Ratio measurement.
Transformer’s winding resistance measurement,
List of measurements and instruments, which could be done with MI 3298 T module
with High Voltage insulation testers (MI 3200, MI 3201, MI 3205, MI 3210):
26
Power Network Application Trainer Introduction MI 3298
Figure 19-1: List of measurements available on Metrel Insulation testers
Insulation Resistance test
Time dependence test – Diagnostic Test
o Dielectric Absorption Ratio (DAR)
o Polarisation index – PI
o Dielectric Discharge – DD
Voltage dependence test – Step Voltage Test
Withstanding Voltage Test
Measurement and instrument, which could be done with MI 3298 T module with
Micro Ohm MI 3250 Voltage insulation testers (MI 3200, MI 3201, MI 3205, MI 3210):
Figure 20-1: “Inductive” measurements mode available on MI 3250 instrument
27
Power Network Application Trainer Introduction MI 3298
Turn ratio
Low limit
High limit
rU / switch position 1,3
9.850
10.300
rU / switch position 2
19.700
20.700
rV / switch position 1, 2, 3
9.850
10.300
rW / switch position 1
9.850
10.300
rW / switch position 2, 3
> 8000.0
> 8000.0
Winding resistance
Low limit [Ω]
High limit [Ω]
RHU
388.0
413.0
RHV
388.0
413.0
RHW
388.0
413.0
RXu / switch position 1,3
4.400
4.650
RXu / switch position 2
2.200
2.400
RXv / switch position 1, 2, 3
4.400
4.650
RXw / switch position 1
4.400
4.650
RXw / switch position 2, 3
> 999.9
> 999.9
HV Test Un=500 V
Low limit
High limit
Riso
5 GΩ
12 GΩ
DAR
1
2
PI
2
6
DD
4 8 Co
54 nF
66 nF
HV Test Un=5 kV
Riso
2 GΩ
12 GΩ
DAR
1 2 PI
2 6 DD
4 8 Co
54 nF
66 nF
1.8.3.1.1 MI 3298 – T: Technical specification
Table 6-1: Turn ratio related to the switch position
Table 7-1: Resistance of primary windings U, V, W related to the switch position
Table 8-1: Technical data of the” HV box” intended for insulation test training
General data:
Dimesnions (w x h x d)..................40 cm x 13,6 cm x 33 cm
Pollution degree............................2
Weight...........................................6,28 kg
Degree of protection ...................... IP 40
Operation conditions:
Working temperature range ......... -10°C ... 50°C
Maximum relative humidity .......... 90 %RH (0°C ... 40 °C), non-condensing
Working nominal altitude.............. up to 3000 m
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Power Network Application Trainer Introduction MI 3298
1.8.3.2 MI 3298 T Training Module
Upon receipt of Demonstration board, it is advisable to check the content of the
delivery. The following items have to be included:
- MI 3298-T puzzle, code 20 919 238
- Puzzle interconnection part 20 052 010
Figure 21-1: MI 3298 T standard set
In case of any module malfunction or any damage notice, the module must be
serviced by a competent service department. Contact your dealer or producer for
further information.
Producer’s contact details:
Address: METREL d.d.
Ljubljanska 77
SI-1354 Horjul
Slovenia, Europe
Tel.: +386 1 755 82 00
Fax.: +386 1 754 92 26
URL: http://www.metrel.si
E-mail: metrel@metrel.si
Use a soft patch slightly moistened with water or alcohol to clean the surface of the
HV Application trainer and leave it to dry totally before use.
Do not use liquids based on petrol!
Do not spill cleaning liquid over the demo board!
29
Power Network Application Trainer Introduction MI 3298
1.8.3.3 MI 3298 T - Warnings and safe rules:
Note:
Follow the instructions for safety work!
Warnings:
Connect instrument according the instructions described in this manual.
For the training purposes and for your safety, use Metrel instruments
described in this manual
Never apply AC voltage on primary or secondary winding terminals; marked as
H (terminals U, V, W) or X (terminals u, v, w), risk of electric shock!
Never apply AC voltage to “pe” terminal. This terminal represents housing of
transformer.
Never touch the test terminals during the performed measurement. Risk of
electric shock
30
Power Network Application Trainer Introduction MI 3298
1.9 Test methods
Metrel instruments for Power (High Voltage) applications:
- MI 3290 Earth Analyzer
- MI 3295S/MI 3295M Step Contact Voltage Measuring system
- MI 3210 TeraOhmXA10kV Insulation resistance measurement system
- MI 3205 TeraOhmXA 5kV Insulation resistance measurement system
- MI 3201 TeraOhm 5kV Insulation resistance measurement system
- MI 3250 MicroOhm 10A Winding resistance measurement
- MI 3280 Digital Transformer analyser
support the standardized test methods according relevant IEC standards (IEC 615575, IEC 62271-100 ,IEC 62271-1, IEC 61326-1)and IEEE Guide for Measuring Earth
Resistivity, Ground Impedance, and Earth Surface Potentials of a Grounding System
(IEEE Std 81-2012).
Test methods supported according IEEE Std 81 – 2012:
Methods of measuring earth resistivity:
Specific Earth Resistance method (four-point) according to the IEEE Std 81 –
2012, item 7.2.3
Method of measuring earth impedance:
Two-point Z earth method according to the IEEE Std 81 – 2012, item 8.2.2.1
Three-point Z earth method according to the IEEE Std 81 – 2012, item 8.2.2.2
Staged fault test method according to the IEEE Std 81 – 2012, item 8.2.2.3
Fall of potential method according to the IEEE Std 81 – 2012, item 8.2.2.4
Clamp-on or stake less method according to the IEEE Std 81 – 2012, item
8.2.2.5
Resistance by fall of potential (FOP) / flex clamp-on method according to the
IEEE Std 81 – 2012, item 8.2.2.6
Z ground by computer based multi-meter method according to the IEEE Std 81
– 2012, item 8.2.2.7
Methods for testing earth potential and step and touch voltages
Staged fault test method according to the IEEE Std 81 – 2012, item 9.4.1
Current injection or low voltage fault test method according to the IEEE Std 81
– 2012, item 9.4.2
Conventional ground meter method according to the IEEE Std 81 – 2012, item
9.4.3
Contact (Touch) / Step by computer based multi-meter method according to
the IEEE Std 81 – 2012, item 9.4.4
Method for testing transient impedance of earthing system:
Impulse generator transient impedance method according to the IEEE Std 81
– 2012, item 12.2
MI 3290 Earth Analyzer supports different measuring methods, divided into different
profiles:
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Power Network Application Trainer Introduction MI 3298
Selected single measurement method could be started from the measurement menu.
In case that user wants to make different measurement methods in one step,
METREL solution provides so called Auto Sequence®, where more measurements
are done in one step. Measurements are done sequentially.
1.9.1 Auto sequence®
The Auto Sequences in the MI 3290 Earth Analyser can be organized in lists of Auto
Sequences (sequence of tests performed in one combined test). In a list, a group of
similar Auto Sequences® is stored. The Auto Sequence groups menu is intended to
manage with different lists of Auto Sequences® that are stored on the microSD card.
Auto sequence’s enable more transparent and faster tests on the field.
1.9.1.1 Auto Sequence® groups menu
In Auto Sequence® groups menu, lists of Auto Sequences® are displayed. Only one
list can be opened in the instrument at the same time. The list selected in the Auto
Sequence® groups menu will be opened in the Auto Sequence® main menu.
Pre-programmed sequences of measurements can be carried out in Auto
Sequence® menu. The sequence of measurements, their parameters and flow of the
sequence can be programmed. The results of an Auto Sequence® can be stored in
the memory together with all related information.
Auto Sequence can be pre-programmed on PC with the Metrel ES Manager software
and uploaded to the instrument. On the instrument parameters and limits of individual
single test in the Auto Sequence can be changed / set.
Auto sequence, which supports standard measurement methods according IEEE Std
81 – 2012 standard is available in the MI 3290 instrument. Each user can adopt
these sequences or prepare own ones with Metrel ES Manager software. Auto
32
Power Network Application Trainer Introduction MI 3298
Sequence’s allow measurements to be made according to standardized procedures
and performing more measurements under same task.
For example: single and sweep frequency 4-Pole measurements performed
automatically under same task.
Figure 22-1: Example of Auto Sequences under IEEE 81 -2012 Auto sequence
1.10 Safety precautions
Test personnel must strictly follow the safety rules before performing any
measurement on the test object. They should be aware, that a lethal potential can
exist between the station ground and remote ground in case that a power-system
fault involving the station ground occurs while ground tests are being made.
Safety precautions are described in the IEEE Std 81-2012 standard.
Safety procedures and practices adopted by the particular organization involved shall
be strictly followed.
1.10.1 Station ground tests
Reduced the hazards by wearing gloves and dielectrically rated footwear.
Exposed test leads and electrodes are isolated from workers and the general
public.
Short test periods assured and all test leads promptly removed after the test is
completed.
Remote probes and test leads are under continuous observation.
Ungrounded ends of test lead’s parallel an energized line mitigated by the
physical orientation of test leads, grounding, or both of them.
Under no circumstances it should be allowed that two hands or other parts of the
body complete the current circuit between points of possible high potential
difference.
1.10.2 Surge arrester ground test
Special care and precautions should be taken for surge arrester ground continuity
tests:
The base of the surge arrester can approach line potential, so never disconnect
the ground of a surge arrester.
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Power Network Application Trainer Introduction MI 3298
Extremely high, short-duration lightning or switching currents can be discharged
into the ground.
A system fault can occur if a surge arrester fails during testing.
1.10.3 Neutral and shield wire ground tests appropriate work procedures
Special care and precautions should be taken also high-potential gradients around
the current electrode.
Disconnecting neutral and shield wires can generate hazardous voltages.
Hazard can occur whether the line is energized or not, due to current flow
through the interconnected shield wires.
1.10.4 Equipment neutral ground test precautions
High voltages can occur if neutrals are disconnected from energized
equipment.
1.11 Warnings
New generation of Metrel products (MI 3290 Earth Analyser, MI 3280 Digital
Transformer Analyser) are equipped with so called “Visual test” sequence which is
used as guidance to maintain safety standards procedure before, during and after
testing, as well as safety precautions according IEEE 81tm /5. Operator needs to go
through the precautions test to be sure, that all safety equipment and measures are
used during the performed tests and all regulations are taken into account.
Visual test is used as guidance to maintain safety standards prior testing and they
are available under icon . Main purpose is to make all safety checks before
performing any test.
1.11.1 Inspectors guide – safety precautions before test
Before performing tests on Power (HV) application field basic safety precautions and
local regulation needs to be followed. Operator needs to assure, that:
Wearing dielectrically rated gloves, helmet and footwear,
Exposed test leads and electrodes are isolated from workers and public prior,
Remote probes and test leads are under continuous observation.
1.11.2 Inspectors guide – safety hazards during test
During the performance of tests on the Power (HV) field it is necessary to take into
account the safety of the surroundings and persons present during the measurement.
It must be ensured, that:
Avoid ungrounded ends of test leads,
Surge arrester can approach line potential,
Never disconnect the ground,
Lightning or switching currents can be discharged into the ground,
34
Power Network Application Trainer Introduction MI 3298
A system fault can occur if a surge arrester fails during testing,
Hazard can occur when disconnecting neutral and shield wires,
Hazard can occur due to current flow through the interconnected shield wires,
High voltages can occur if neutrals are disconnected from energized
equipment.
1.11.3 Inspectors guide – after test reminder
After completing the tests, operator is responsible that:
All test leads promptly removed after the test is completed.
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Power Network Application Trainer – Earthing / Grounding network impedance measurement
Earth / Ground network impedance analysing
Figure 23-1: Set of Metrel measuring instruments, which could be used with MI 3298 P1
Topics covered:
Lightning protection
Substations
Transformers
Transmission lines
Towers
Pylons
Measurement instruments used
MI3290
MI3295S
MI3295M
MI 3123
36
Power Network Application Trainer – Earthing / Grounding network impedance measurement
2 Earthing and Grounding resistance measurements .......................................... 42
2.1 Basic theory about earthing ........................................................................................................ 42
2.2 Specific earth resistance measurements [ρ] ............................................................................... 44
2.2.1 Wenner method measurement .......................................................................................... 46
2.2.2 Schlumberger method measurement ................................................................................. 46
2.3 Earth resistance measurement [Ze and Re] ................................................................................ 48
2.3.1 Functionality and placing of test probes ............................................................................. 48
2.3.1.1 Straight-line placement ................................................................................................... 49
2.3.1.2 Equilateral placement ..................................................................................................... 51
2.3.1.3 Test probe resistances .................................................................................................... 51
2.3.2 Earth resistance measurements method ............................................................................ 53
2.3.2.1 2–pole measurement – single frequency and sweep mode up to 15 kHz ...................... 57
2.3.2.2 3–pole measurement – single frequency and sweep mode up to15 kHz....................... 57
2.3.2.3 4–pole measurement – single frequency and sweep mode up to 15 kHz ...................... 58
2.3.2.4 Selective (Iron Clamp) Measurement – single frequency and sweep mode up to
1.5 kHz .............................................................................................................................. 59
2.3.2.5 2 Clamps Measurement – single frequency and sweep mode up to 329 Hz .................. 59
2.3.2.6 HF-Earth Resistance (25 kHz) measurement .................................................................. 60
2.3.2.7 Selective (Flex Clamps 1 - 4) measurement – single frequency and sweep mode
up to 1.5 kHz ..................................................................................................................... 61
2.3.2.8 Passive (Flex Clamps) Measurement .............................................................................. 62
2.4 Pylon Ground Wire Test (PGWT) ................................................................................................ 64
2.5 Impulse impedance [Zp] ............................................................................................................. 65
3 Earth Potential ....................................................................................................... 69
3.1 Ground Potential Rise, Step Voltage, Contact Voltage ............................................................... 70
3.1.1 Ground Potential Rise ......................................................................................................... 70
3.1.2 Step & contact voltage measurement ................................................................................ 72
4 Exercises on MI 3298 P1 training module ........................................................... 75
4.1 Earth resistance measurement exercises ................................................................................... 81
4.1.1 3-Pole and 4-Pole earth resistance measuring method ..................................................... 81
4.1.1.1 Measurement with MI 3290 Earth Analyzer ................................................................... 81
4.1.1.1.1 3 Pole measuring method ........................................................................................... 81
4.1.1.1.2 4 Pole measuring method ........................................................................................... 84
4.1.1.2 Measurement with MI 3123 SmartTEC (Earth/Clamp) meter ........................................ 87
4.1.1.3 Measurement with MI 3295S Step Contact Voltage Measuring System ........................ 89
4.1.2 4 Pole measuring method – simulated different test object state ..................................... 92
4.1.2.1 Simulation of inductive earth character, regular pylon foot’s condition ....................... 92
4.1.2.2 Simulation of resistance earth character and broken pylon’s foot connection ............. 94
4.1.2.3 Simulation of resistance/inductive earth character, regular foot’s condition and
simulated Ground Wire connection ................................................................................ 95
4.1.3 S – Flex measuring method by using one Flex-clamp ......................................................... 98
4.1.3.1 S – Flex measuring method by using one Flex- clamp with simulated regular pylon’s
foot condition and resistance earth character ............................................................................... 98
4.1.3.2 S – Flex measuring method by using one Flex-clamp with simulated broken foot
resistance and resistive earthing type .......................................................................................... 101
4.1.3.3 S – Flex measuring method by using one Flex-clamp - regular foot resistance/ - resistive
earthing type - simulated ground wire connection ...................................................................... 104
4.1.3.4 S – Flex measuring method by using one Flex-clamp - regular foot resistance/inductive
earthing type/simulated ground wire connection ........................................................................ 106
4.1.3.5 S – Flex measuring method by using one Flex-clamp with simulated regular pylon’s foot
condition and resistance earth character ..................................................................................... 108
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Power Network Application Trainer – Earthing / Grounding network impedance measurement
4.1.3.5.1 S – Flex measuring method by using one Flex-clamp with simulated regular pylon’s
foot condition and resistance earth character – measuring of two foots together ..................... 109
4.1.3.5.2 S – Flex measuring method by using one Flex-clamp with simulated regular pylon’s
foot condition and resistance earth character – measuring of all four foots together ................ 111
4.1.4 PGWT measuring method – resistance type with/without simulated GW connection ... 113
4.1.5 HF measuring method – resistance/inductive type with simulated GW connection ....... 117
4.1.6 Auto Sequences® .............................................................................................................. 120
4.1.6.1 Auto Sequence procedure- 4-pole and S - Flex measuring method – resistance type –
simulated broken foot resistance/resistive earthing type ............................................. 121
4.1.6.2 Auto Sequence procedure - 4-Pole/ HF measuring method / S-Flex– broken earth
connection with simulated GW connection ................................................................... 125
4.1.7 Impulse measuring method .............................................................................................. 131
4.2 Step& Contact Voltage Measurement exercises ...................................................................... 135
4.2.1 Step voltage measurement with Earth Analyser MI 3290 ................................................ 135
4.2.2 Step voltage measurement with Step/Contact instrument MI 3295S and MI 3295M ..... 139
4.2.3 Contact(Touch) voltage measurement with Earth Analyser MI 3290 .............................. 142
4.2.4 Contact (Touch) voltage measurement with Step/Contact instrument MI 3295S and
MI 3295M .......................................................................................................................... 145
4.3 GPR Measurement exercises .................................................................................................... 148
4.3.1 Ground Potential Rise measurement – straight line measurement (MI 3290) ................ 149
4.3.2 Ground Potential Rise measurement – straight line measurement
(MI 3290 & MI 3295M) ..................................................................................................... 152
4.3.3 Ground Potential Rise measurement – straight line measurement
(MI 3295S & MI 3295M).................................................................................................... 158
38
Power Network Application Trainer – Earthing / Grounding network impedance measurement
Figure 24-2: Presentation of specific earth resistance ................................................................................ 44
Figure 25-2: Specific resistance measurement: probe distance vs depth of measurement ...................... 45
Figure 26-2: Wenner method for specific earth resistance measurements ................................................ 46
Figure 27-2: Schlumberger method for specific earth resistance measurements ...................................... 46
Figure 28-2: Placement of measuring probes (62% method) ..................................................................... 48
Figure 29-2: Definition of parameter “a” ..................................................................................................... 49
Figure 30-2: Straight-line measuring probes placement ............................................................................. 49
Figure 31-2: Equilateral placement ............................................................................................................. 51
Figure 32-3: Different measured voltage drops at low and high probe resistance ..................................... 52
Figure 33-2: MI 3290 – Earth Analyser and MI 3295S–Step Contact Voltage Measuring System ............ 53
Figure 34-2:MI 3123 - Hand-held installation Smartec Earth / Clamptester ...................................................... 53
Figure 35-2: 2 – pole measurement ............................................................................................................ 57
Figure 36-2: 3 – pole measurement ............................................................................................................ 58
Figure 37-2: 4 – pole measurement ............................................................................................................ 58
Figure 38-2: Selective (Iron Clamp) measurement ..................................................................................... 59
Figure 39-2: 2 Clamps measurement ......................................................................................................... 60
Figure 40-2: HF-Earth Resistance (25 kHz) measurement ........................................................................ 60
Figure 41-2: Compensation of inductive component with HF 25 kHz method ............................................ 61
Figure 42-2: Selective (Flex Clamps 1-4) measurement ............................................................................ 61
Figure 43-2: Passive (Flex Clamps) measurement .................................................................................... 62
Figure 44-2: Substitute circuit for Passive (Flex Clamps) measurement .................................................... 63
Figure 45-2: Pylon Ground Wire Test (PGWT) example ............................................................................ 64
Figure 46-2: Impulse Measurement example ............................................................................................. 66
Figure 47-2: Typical Impulse shape short-circuit ........................................................................................ 66
Figure 48-2: Influence of inductive impedance part at impulse measurement ........................................... 67
Figure 49-2: Influence of inductive impedance part at 3-pole measurement .............................................. 68
Figure 50-2: Dangerous voltages on a faulty earthing system ................................................................... 69
Figure 51-2: Example of ground potential measurement............................................................................ 71
Figure 52-2: Potential gradient measurements example (straight line) ...................................................... 71
Figure 53-2: Test step/contact voltage plates and 25kg probes ................................................................. 73
Figure 54-2: Step voltage measurement with MI3290 instrument .............................................................. 73
Figure 55-2: Step voltage measurement with MI3295S & MI3295M instruments ...................................... 74
Figure 56-2: Contact voltage measurement with MI3290 instrument ......................................................... 74
Figure 57-2: Contact voltage measurement with MI3295S & MI3295M instruments ................................. 74
Figure 58-2: Set of Metrel instruments used with MI 3298 P1 training module .......................................... 75
Figure 59-2: Available measurement on the MI 3290 Earth Analayser ...................................................... 75
Figure 60-2: 3-pole earth resistance measurement with MI 3290 .............................................................. 81
Figure 61-2: 4-pole earth resistance measurement with MI 3290 .............................................................. 84
Figure 62-2: Earth measurement with MI 3123 .......................................................................................... 87
Figure 63-2: Earth measurement with MI 3295S ........................................................................................ 89
Figure 64-2: 4-pole earth measurements setup with MI 3290 .................................................................... 92
Figure 65-2: 4-pole earth measurements setup with MI 3290 .................................................................... 94
Figure 66-2: 4-pole earth measurements setup with MI 3290 .................................................................... 95
Figure 67-2: S-Flex measurement setup with MI 3290 ............................................................................... 98
Figure 68-2: S-Flex measurement setup with MI 3290 ............................................................................. 101
Figure 69-2:S-Flex measurement setup ................................................................................................... 104
Figure 70-2: S-Flex measurement setup .................................................................................................. 106
Figure 71-2: S-Flex measurement setup for measuring two pylon foot’s ................................................. 109
Figure 72-2: S-Flex measurement setup for measuring all pylon foots .................................................... 111
Figure 73-2: PGWT measurement setup .................................................................................................. 113
Figure 74-2: PGWT measurement setup with connected ground wire ..................................................... 115
Figure 75-2: HF measuring method setup ................................................................................................ 117
Figure 76-2: Example of Auto Sequence window ..................................................................................... 120
Figure 77-2: 4-pole and S-Flex measurement setup ................................................................................ 121
Figure 78-2: Auto sequence setup (4-pole and S-Flex) ............................................................................ 122
Figure 79-2: 4-pole, HF and S-Flex measurement setup ......................................................................... 125
Figure 80-2: Auto sequence setup (4-pole, HF and S-Flex) ..................................................................... 126
Figure 81-2: Impulse measuring method setup ........................................................................................ 131
39
Power Network Application Trainer – Earthing / Grounding network impedance measurement
Figure 82-2: Impulse measuring method setup with GW conenction ....................................................... 133
Figure 83-2: Step voltage setup with MI 3290 .......................................................................................... 136
Figure 84-2: Step voltage setup with MI 3295S ........................................................................................ 139
Figure 85-2: Contact (Touch) voltage setup with MI 3290 ........................................................................ 142
Figure 86-2: Contact (Touch) voltage setup with MI 3295S ..................................................................... 145
Figure 87-2: GPR measuring method with MI 3290 ................................................................................. 149
Figure 88-2: Test point selection for GPR measurement ......................................................................... 150
Figure 89-2: GPR measuring method with MI 3290 & MI 3295M ............................................................. 153
Figure 90-2: Selection of test point for GPR measurements .................................................................... 154
Figure 91-2: Graphical presentation of GPR measurements.................................................................... 157
Figure 92-2: GPR measurement with MI 3290 ......................................................................................... 158
Figure 93-2: Graphical presentation of GPR measurements.................................................................... 161
40
Power Network Application Trainer – Earthing / Grounding network impedance measurement
Table 9-2: Specific earth resistance ............................................................................................................ 44
Table 10-2: Measurement result uncertainty vs d1/a1 ................................................................................ 50
Table 11-2: Permissible body current IB and calculated values of the permissible touch
voltage UTp depending on the fault duration tf ........................................................................ 70
Table 12-2: Exercises – Earth resistance measurements .......................................................................... 76
Table 13-2: Exercises – GPR & Step/Contact measurements ................................................................... 80
Table 14-2: Measurement setup/result for 3-pole measurement method ................................................... 81
Table 15-2: Measurement setup/result for 3-pole measurement method ................................................... 84
Table 16-2: Measurement setup/result for 4-wire measurement method with MI 3123 ............................. 87
Table 17-2: Measurement setup/result for 4-wire measurement method with MI 3295S ........................... 89
Table 18-2: Result comparison for 3-pole and 4-pole measurement done with different instruments ....... 91
Table 19-2: Measurement setup/result for 4-pole method .......................................................................... 92
Table 20-2: Measurement setup/result for 4-pole method with simulated error ......................................... 94
Table 21-2: Measurement setup/result for 4-pole method with different test object condition ................... 96
Table 22-2: Result comparison: same test method vs different test object setup ...................................... 97
Table 23-2: S-Flex measurement setup/result ............................................................................................ 98
Table 24-2: Pylon foot’s impedance .......................................................................................................... 101
Table 25-2: S-Flex measurement setup/result presentation ..................................................................... 102
Table 26-2: Pylon foot’s impedance .......................................................................................................... 103
Table 27-2: S-Flex measurement setup/result presentation ..................................................................... 104
Table 28-2: Pylon foot’s impedance .......................................................................................................... 106
Table 29-2: S-Flex measurement setup/result presentation ..................................................................... 106
Table 30-2: Pylon foot’s impedance .......................................................................................................... 108
Table 31-2: Flex clamp installation ........................................................................................................... 108
Table 32-2: S-Flex measurement setup/result presentation ..................................................................... 109
Table 33-2: Pylon foot’s impedance .......................................................................................................... 110
Table 34-2: S-Flex measurement setup/result presentation ..................................................................... 111
Table 35-2: S-Flex measurement result comparison ................................................................................ 112
Table 36-2: PGWT measurement setup/result presentation .................................................................... 113
Table 37-2: PGWT result comparison ....................................................................................................... 116
Table 38-2: HF measurement method setup/result presentation ............................................................. 117
Table 39-2: Result comparison: test object setup vs measurement method ............................................ 119
Table 40-2: 4-pole and S-Flex setup/result presentation .......................................................................... 121
Table 41-2: 4-pole, HF and S-Flex setup/result presentation ................................................................... 125
Table 42-2: Pylon’s foot impedance calculation ....................................................................................... 129
Table 43-2: Result comparison (measurement method vs test object setup) .......................................... 130
Table 44-2: Impulse measuring method setup/result presentation ........................................................... 131
Table 45-2: Impulse measuring method setup/result presentation ........................................................... 133
Table 46-2: Result comparison (Impulse method vs different test object setup) ...................................... 134
Table 47-2: Step voltage measuring method setup/result presentation ................................................... 135
Table 48-2: Step voltage measuring method setup/result presentation ................................................... 139
Table 49-2: Contact (Touch) voltage measuring method setup/result presentation ................................. 142
Table 50-2: Contact (Touch) voltage measuring method setup/result presentation ................................. 146
Table 51-2: GPR measuring method setup/result presentation ............................................................... 149
Table 52-2: GPR measuring method setup/result presentation ............................................................... 152
Table 53-2: GPR measuring method setup/result presentation ............................................................... 158
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Power Network Application Trainer – Earthing / Grounding network impedance measurement
Measuring method
According to standard
2 – pole
3 – pole
4 – pole
EN 61557 – 5 [Resistance to earth]
IEEE Std 81 – 2012 [Two-point method, Three-point
method, Fall-of-potential method]
2 Clamps
IEEE Std 81 – 2012 [Resistance measurements by
clamp-on stake-less method]
2 Earthing and Grounding resistance measurements
2.1 Basic theory about earthing
The basic rule to ensure safety on any object (residential/industrial) is to provide proper
and good grounding. Without or not proper grounding people lives could be threatened
and equipment damaged. Correct earthing of exposed conductive parts of the object
assures that the voltage on them stays below dangerous level in case of a fault. If fault
happens a fault current will flow through the earthing electrode. Metrel experts propose
regular testing to ensure proper operating conditions.
Earth resistance (impedance) value is normally rated in few ohms. We suggest
checking the applicable standards and national regulations before performing
measurements.
How earthing (earthing electrode) is done, depends on national regulation, building
regulations and standards. Typically, is done from:
Strips, tubes
underground earth loop
metal strip or cable sunk into the building concrete
metal plates
in different form, like: star, ring shaped, network meshes, ….
Earth resistance is not concentrated in one point but it is distributed around whole
electrode. If a faulty current flow through the earth electrode, then a typical distribution
of the voltage occurs around it (voltage funnel). Maximum voltage drop is concentrated
around the earth electrode.
Earthing system measurement is normally done after installation to check if the
measured result meets the design criteria. Metrel also propose to perform periodically
measurements to ensure the earthing system is in proper condition (effect of corrosion,
changes in the soil resistivity etc.)
MI 3290 Earth Analyzer measuring methods are designed according relevant standards
and support different measuring methods:
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Power Network Application Trainer – Earthing / Grounding network impedance measurement
Selective (Flex Clamps 1 – 4)
Selective (Iron Clamp)
IEEE Std 81 – 2012 [Resistance measurements by
FOP/clamp-on method]
CIGRE Working Group C4.2.02 [Methods for
measuring the earth resistance of transmission
towers equipped with earth wires]
HF Earth Resistance (25 kHz)
IEEE Std 81 – 1983 [High-Frequency Earth
Resistance Meter]
CIGRE Working Group C4.2.02 [Methods for
measuring the earth resistance of transmission
towers equipped with earth wires]
Pylon ground wire test
Wenner Method
Schlumberger Method
IEEE Std 81 – 2012 [Four-point method (Equally
Spaced or Wenner Arrangement); (Unequally Spaced
or Schlumberger-Palmer Arrangement)]
Ω - Meter (200mA) (also 7 mA)
EN 61557 – 4 [Resistance of earth connection and
equipotential bonding]
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Power Network Application Trainer –Earthing / Grounding network impedance measurement
Type of ground material
Specific earth resistance
in Ωm
Specific earth resistance
in Ωft
sea water
0,5
1,6
lake or river water
10 – 100
32,8 – 328
ploughed earth
90 – 150
295 – 492
concrete
150 – 500
492 – 1640
wet gravel
200 – 400
656 – 1312
fine dry sand
500
1640
lime
500 – 1000
1640 – 3280
dry gravel
1000 – 2000
3280 – 6562
stony ground
100 – 3000
328 – 9842
2.2 Specific earth resistance measurements [ρ]
The measurement is carried out in order to assure more accurate calculation of earthing
systems e.g. for high-voltage distribution towers, large industrial plants, lightning
systems etc.
AC test voltage is used for the measurement, since DC test voltage is not suitable due
to possible electro-chemical processes in the measured ground material. Specific earth
resistance value is expressed in Ωm or Ωft, its absolute value depends on structure of
the ground material.
Specific earth resistance is resistance of ground material shaped as a cube 1 m × 1 m ×
1 m, where the measurement electrodes are placed at the opposite sides of the cube.
Figure 24-2: Presentation of specific earth resistance
Conduction of current in the soil is mostly electrolytic, so the amount of moisture and
salt content in soil radically affects to its resistivity. Since the amount of water in the soil
varies related to the weather conditions, groundwater level, seasons, different layer soil
structure as well as temperature (increase of temperature leads to decrease of
resistance) the earth resistance vary a lot during the year’s seasons.
Indicative values of specific earth resistances for a few typical ground materials are
presented in the table below:
For soil structure analyse it is recommended to perform more measurement with
different distance between test probes. Higher distance between probes means, that
deeply depth of soil is analysed. Example bellow shows relation between probe
distance and measured soil depth.
Table 9-2: Specific earth resistance
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Power Network Application Trainer – Earthing / Grounding network impedance measurement
Figure 25-2: Specific resistance measurement: probe distance vs depth of measurement
With such measurements it is also possible to determine more (different) layer soil
structure and also layer depth.
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Power Network Application Trainer – Earthing / Grounding network impedance measurement
2.2.1 Wenner method measurement
Four earth probes are placed on a straight line, at a distance “a” from one another and
at depth b < a/20. Distance “a” must be between 0,1 m and 29,9 m.
Figure 26-2: Wenner method for specific earth resistance measurements
Specific earth resistance according to Wenner method:
where:
Re ....................................... Measured earth resistance in 4-pole method
a ......................................... Distance between earth probes
b ......................................... Depth of earth probes
π ......................................... Number π is a mathematical constant (3.1416)
2.2.2 Schlumberger method measurement
ES and S earth probes are located at a distance “d” from one another and other two
earth probes (E and H) at distance “a” from ES and S probes (see Figure 13-3 below).
All probes must be placed on a straight line and to a depth of “b”, considering the
condition b << a and d. Distance “d” must be between 0,1 m and 29,9 m and the
distance “a” must be a>2*d.
Figure 27-2: Schlumberger method for specific earth resistance measurements
46
Power Network Application Trainer – Earthing / Grounding network impedance measurement
where:
Re ....................................... Measured earth resistance in 4-pole method
a ......................................... Distance between earth probes (E, ES) and (H, S)
d ......................................... Distance between earth probes (S, ES)
π ......................................... Number π is a mathematical constant (3.1416)
Metrel recommends performing more measurements with changing the distance
between electrodes (“a” and “d”) as well as the depth (b) of electrodes. By changing the
electrodes depth “b”, also deeper ground layers will be taken into account.
Simplified formulas for calculation of earth resistance for different earthing types:
a) Earth resistance for square metal plate with the page of the square “a”
b) Earth resistance for vertical rod, with the length “l”
c) Earth resistance for the metal strip, with the length “l”
It is important to consider, that the lightning strike current is effective in the range of 20
meters (where earth system inlet to the ground).
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Power Network Application Trainer – Earthing / Grounding network impedance measurement
2.3 Earth resistance measurement [Ze and Re]
Earth resistance measurement is one of the most important parameters for protection
against electric shock. Correct earthing of exposed conductive parts of the object
assures that the voltage on these parts stay below dangerous level in case of a fault or
lightning strike. In such case, a fault current will flow through the earthing electrode.
Fault currents close to power distribution objects (substations, distribution towers, power
generations, industrial plants) can be very high, also up to 200 kA, which can cause
high (dangerous) voltages on conductive parts due to the improper earthing.
In the practice it is not always easy to acquire earth electrode which ensures sufficient
earth resistance. We must be aware that the earth resistance is changing during the
yearly seasons.
Metrel recommends periodical testing of earth resistance to ensure safety operation in
case of fault.
2.3.1 Functionality and placing of test probes
For a standard earthing resistance two test probes (voltage and current electrode) are
used. Because of the influence of voltage funnel, it is important, that the test electrodes
are placed correctly. More information about principles described in this document can
be found in the handbook: Grounding, bonding, and shielding for electronic equipment
and facilities.
Figure 28-2: Placement of measuring probes (62% method)
Correct probes placing is essential. If the S probe is placed too close to the earthing
system, then too small resistance will be measured (only a part of the voltage funnel
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Power Network Application Trainer – Earthing / Grounding network impedance measurement
would be taken into account). If the S probe is placed too close to the H probe the
earthing resistance of voltage funnel of the H probe would disturb the result.
According the theory, probe S should be placed on the distance of 62% from the probe
E(ES). This rule works well for simple electrodes (like a driven rod), as well as for a
small group of rods. For such cases, the true electrical centre of the electrode system
should be known quite accurately. Accuracy of the measured result is better if the earth
resistance between the electrodes is pretty constant.
Parameter “a” represents the maximum dimension of the earthing electrode (or a
system of electrodes) and can be defined according to Figure 17-3.
Figure 29-2: Definition of parameter “a”
Buried metal objects (water pipeline), nearby railway, lakes, river etc. cause local
deviations and could influence to the measurements.
2.3.1.1 Straight-line placement
Figure 30-2: Straight-line measuring probes placement
a1 .............. distance between connection point of earthing system and centre (radius of
the object)
After defining the maximum dimension “a1” of an earthing system, the proper placement
of test probes could be defined. Metrel propose to perform measurement with three
different placements of test probe S (S’’, S, S’) to verify that the selected distance d1 is
long enough.
Good practice:
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Power Network Application Trainer – Earthing / Grounding network impedance measurement
d1/a1
Uncertainty [%]
5
10
10 5 50
1
Distance “d1” from tested earthing electrode system E/ES to current probe H
shall be: d1 ≥ 5•a1
Distance “d2” from tested earthing electrode system E/ES to potential probe S
shall be:
Measurement 1:
Distance from earthing electrode E/ES to voltage probe S shall be:
d2 = 0.62•d1
Measurement 2:
Distance from earthing electrode E/ES to voltage probe S’’ shall be:
d2 = 0.52•d1
Measurement 3:
Distance from earthing electrode E/ES to voltage probe S’ shall be:
d2 = 0.72•d1
In case of properly selected “d1” the result of measurements 2 and 3 are symmetrical
around the result of measurement 1. The difference between (measurement 2measurement 1) and (measurement 3 - measurement 2) must be lower than 10 %.
Higher differences or non-symmetric results mean that the voltage funnels influence the
measurement and the distance d1 should be increased.
Notes:
Initial uncertainty of measured resistance to earth depends on distance between
electrodes d1 and size of earthing electrode a.
Table 10-2: Measurement result uncertainty vs d1/a1
It is recommended to repeat the measurement at different placements of test
probes.
The test probes shall also be placed in the opposite direction from tested
electrode (180° or at least 90°). The final result is an average of two or more
partial results.
According to the standard IEC 60364-6 the distances between S’-S
(measurement 2) and S’’-S (measurement 3) shall be 6 m.
Metrel recommends unrolling the whole cable from the cable reel to avoid
electromagnetic interference. Cable should not form loops and should not be
placed close to each other or parallel to other metal conductors.
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Power Network Application Trainer – Earthing / Grounding network impedance measurement
2.3.1.2 Equilateral placement
Figure 31-2: Equilateral placement
Measurement 1:
Distance “d1” from tested earthing electrode E/ES to current probe H and voltage probe
S to E/ES (H) should be at least: d1 = 5•a
Probes E/ES, H and S should form an equilateral triangle.
Measurement 2
Position of voltage probe S’ is contrary side regarding to H, at same distances “d1”
between test probes. Probes E/ES, H and S’ should form an equilateral triangle.
The difference between both measurements shall not exceed 10%. If a difference in
excess of 10% occurs, distance d1 should be proportionally increased and both
measurements repeated. A simple solution is only to exchange test probes S and H
(can be done at the instrument side). The final result is an average of two or more
partial results.
It is advisable for the measurement to be repeated at different placements of test
probes. The test probes shall be placed in the opposite direction from tested electrode
(180° or at least 90°).
MI 3290 gives you the status about performed measurement in case of present
disturbances:
Consider warnings presented on the display when starting the measurement!
Take care about the “noise” warning presented on the LCD in case, that high
noise currents and voltages in earth could influence the measurement results
When measuring at high frequencies use the guard terminal and shielded cable
for test probe H.
2.3.1.3 Test probe resistances
Test probes should have a low resistance to earth. In case that the test probe
resistance is too high (usually because of dry soil) the H and S probes can significantly
influence to the measurement result. High resistance of H probe means that most of the
voltage drop is concentrated at the current probe and the measured voltage drop of the
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Power Network Application Trainer – Earthing / Grounding network impedance measurement
tested earth electrode is small. High resistance of S probe can form a voltage divider
with the internal impedance of the test instrument resulting in a lower test result. Test
probe resistance can be reduced by:
Watering the soil around probes with normal or salty water.
Depleting electrodes under dried surface.
Increasing test probe size or paralleling of probes.
METREL test equipment displays appropriate warnings in such case, according to IEC
61557-5. All METREL Earth testers measure accurate at probe resistances far beyond
the limits in IEC 61557-5.
Figure 32-3: Different measured voltage drops at low and high probe resistance
Notes:
High impedance of S and H probes could influence the measurement results. In
such case, “Rp” and “Rc” warnings are displayed on the MI 3290 Earth Analyser.
There is no pass / fail indication in this case.
Probes must be placed at a sufficient distance from the measured object.
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Power Network Application Trainer – Earthing / Grounding network impedance measurement
2.3.2 Earth resistance measurements method
Main installation earthing arrangements, like lightning systems, local earthing’s, etc. can
be verified with the MI 3290 Earth Analyser. MI 3290 is able to carry out earth
measurement using different measuring methods. The appropriate one should be
selected by the operator depending on the particular earthing system to be tested.
Metrel offers different type instruments, which could be used for earthing
measurements:
Figure 33-2: MI 3290 – Earth Analyser and MI 3295S–Step Contact Voltage Measuring System
Figure 34-2:MI 3123 - Hand-held installation Smartec Earth / Clamptester
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Power Network Application Trainer – Earthing / Grounding network impedance measurement
Earth resistance measurement methods available on MET
REL instruments MI 3290 and MI 3123
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Power Network Application Trainer – Earthing / Grounding network impedance measurement
55
Power Network Application Trainer – Earthing / Grounding network impedance measurement
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Power Network Application Trainer – Earthing / Grounding network impedance measurement
2.3.2.1 2–pole measurement – single frequency and sweep mode up
to 15 kHz
The two-pole measurement can be used in case, that there is a well-grounded auxiliary
terminal available (e.g. source/ distribution earthing’s via the neutral conductor, water
pipeline…). The main advantage of this method is that no test probes are needed for
the test. The method is fast and relatively reliable, but practical usage is limited with the
existing well-grounded system.
Figure 35-2: 2 – pole measurement
Notes:
AC test current Ie is injected through the test probe H (fixed or sweep mode, 55
Hz … 15 kHz),
Impedance of probe H should be as low as possible (to inject higher test current),
Existing grounded system (conductive water pipeline) should be “good” enough,
that its resistance is negligible,
Measured earthing system should be far enough away from the water pipeline
system to be outside its influence.
2.3.2.2 3–pole measurement – single frequency and sweep mode up to15 kHz
The 3 - pole measurement is the standard earthing test method. The measurement is
performed with two earthing probes (H and S), the third one is tested earthing electrode
system. The drawback by using 3 – pole measurement method is that the resistance of
the common test lead (E) is added to the final result.
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Power Network Application Trainer – Earthing / Grounding network impedance measurement
Figure 36-2: 3 – pole measurement
Notes:
AC test current Ie is injected through the test probe H (fixed or sweep mode, 55
Hz … 15 kHz)
Impedance of probe H should be as low as possible (to inject higher test current),
Voltage drop is measured between probe S and E,
Use short test lead E, to minimize its influence in the final result.
2.3.2.3 4–pole measurement – single frequency and sweep mode up to 15 kHz
The advantage for using of 4 - pole test is that the leads and contact resistances
between measuring terminal E and tested item do not influence the measurement.
Figure 37-2: 4 – pole measurement
Notes:
AC test current Ie is injected through the test probe H (fixed or sweep mode, 55
Hz … 15 kHz),
Impedance of probe H should be as low as possible (to inject higher test current),
Voltage drop is measured between probe S and ES,
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Power Network Application Trainer – Earthing / Grounding network impedance measurement
4 – pole method is useful for measuring low resistance,
Test leads should be separated and not placed close and parallel to each other
(eliminating mutual inductance),
2.3.2.4 Selective (Iron Clamp) Measurement – single frequency and sweep mode up to 1.5 kHz
This measurement is applicable for measuring selective earth resistances of individual
earthing points in a complex earthing system (multiple grounds in parallel). The earthing
electrodes do not need to be disconnected during measurement.
Figure 38-2: Selective (Iron Clamp) measurement
Notes:
AC test current Ie is injected through the test probe H (fixed or sweep mode; 55
Hz … 1.5 kHz)
Impedance of probe H should be as low as possible (to inject higher test current),
Voltage drop is measured between probe S and ES,
Selective current Ic is measured through the selected earthing electrode Ze1 by
current clamps
Selected impedance Ze1 is determined by the voltage measured on the S – ES
terminals and current Ic measured by the current clamps.
2.3.2.5 2 Clamps Measurement – single frequency and sweep mode up to 329 Hz
This measurement method is used for measuring earth impedances of grounding rods,
cables, under- earth connections, etc. The measuring method needs a closed loop to be
able to generate test currents. It is especially suitable for use in urban areas because
there is usually no possibility to place the test probes.
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Power Network Application Trainer – Earthing / Grounding network impedance measurement
Figure 39-2: 2 Clamps measurement
Two current clamps are used: generator and measuring current clamps. The driver
(generator) clamp injects a voltage (current) in the earthing system (loop).
If the total loop earth impedance of the electrodes Ze1, Ze2 and Ze3 connected in parallel
is much lower than the impedance of tested electrode Ze4, then the result can be
considered as ~ Ze4. Other individual impedance could be measured on the same
manner.
Notes:
AC test current Ie is injected through the generator current clamps (fixed or
sweep mode; 82 Hz … 329 Hz)
2.3.2.6 HF-Earth Resistance (25 kHz) measurement
The high frequency measuring method offers the advantage of eliminating the influence
of adjacent tower earthing’s connected by overhead grounding wire (automatic
compensation of inductive components).
Figure 40-2: HF-Earth Resistance (25 kHz) measurement
60
Power Network Application Trainer – Earthing / Grounding network impedance measurement
Notes:
AC test current Ie is injected through the test probe H (25 kHz)
Impedance of probe H should be as low as possible (to inject higher test current),
Voltage drop is measured between probe S and E,
Earth resistance Re is determined from the voltage U
S-E
and Ie.
HF-Earth resistance (25 kHz) measurement method automatic compensate inductive
components of the adjacent pylons.
Figure 41-2: Compensation of inductive component with HF 25 kHz method
Note:
Typical ground wire inductance in power lines 0.2 mH – 200 mH
2.3.2.7 Selective (Flex Clamps 1 - 4) measurement – single frequency and sweep mode up to 1.5 kHz
This measurement is applicable for measuring selective earth resistances of individual
earthing points in an earthing system (example: pylon foots, antenna towers etc.). The
earthing rods do not need to be disconnected during measurement.
Figure 42-2: Selective (Flex Clamps 1-4) measurement
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Power Network Application Trainer – Earthing / Grounding network impedance measurement
Notes:
AC test current Ie is injected through the test probe H (55 Hz … 1.5 kHz),
Impedance of probe H should be as low as possible (to inject higher test current),
Voltage drop is measured between probe S and ES,
The selective currents I
is measured through the earthing electrodes Z
f1-4
(pylon foots) selected by the user,
The selected earth impedance Z
selected current (external current clamp – I
is determined from the voltage U
sel1-4
) ratio.
f1-4
S-ES
When using only one, two or three flex clamps, always connect one clamp to F1
terminal (synchronization port).
Make sure that the arrow marked on the clamp coupling points toward the correct
orientation for correct phase measurement.
Make sure that the number of turns is correctly entered in the test parameters
window
sel1-4
and
2.3.2.8 Passive (Flex Clamps) Measurement
The passive measuring method use the “Inductive current” or grounding wire current I
flowing in the earthing system to determine the selected earth resistances of individual
earthing points (pylon foot). This passive method is useful for checking the consistency
of the measurements obtained with the selective (Flex Clamps 1 - 4) measurement
method.
gw
Figure 43-2: Passive (Flex Clamps) measurement
“Inductive current” - Igw is actually an inductive coupling current between wires L1 (i1),
L2 (i2), L3 (i3) and overhead grounding wire line. This current has the same frequency
as the currents in lines L1, L2 and L3 (usually power frequencies 50 Hz or 60 Hz).
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Power Network Application Trainer – Earthing / Grounding network impedance measurement
Figure 44-2: Substitute circuit for Passive (Flex Clamps) measurement
Notes:
Inductive current Igw flows into earth through Z
sel1/1
, Z
sel2/1
, Z
sel1/2
and Z
sel2/2
The voltage drop is measured by auxiliary potential probe (S).
The selective currents I
is measured through the earthing electrode Zsel
f1-4
1-4/1
(pylon foots) selected by the user.
The selected earth impedance Z
sel1-4/1
selected current (external current clamp – I
is determined from the voltage U
) ratio.
f1-4
S–E
and
When using only one, two or three flex clamps, always connect one clamp to F1
terminal (synchronization port).
Make sure that the arrow marked on the clamp coupling points toward the correct
orientation for correct phase measurement.
Make sure that the number of turns is correctly entered in the test parameters
window
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Power Network Application Trainer – Earthing / Grounding network impedance measurement
2.4 Pylon Ground Wire Test (PGWT)
The PGWT measurement is performed to check the overhead grounding wire
connection.
Figure 45-2: Pylon Ground Wire Test (PGWT) example
During the measurement a sinusoidal current Igen is injected into the earth through an
auxiliary probe (H). The resistance of the auxiliary probe (H) should be as low as
possible in order to inject a high-test current. The resistance Rc can be decreased by
using more probes in parallel. A higher injected current improves the immunity against
spurious earth currents.
In the example following current Ig_w is measured according to following equation:
where:
I
..........Overhead ground wire current
g_w
I
..........Generator current (injected test current)
gen
I
........Total flex clamp current
f_sum
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Power Network Application Trainer – Earthing / Grounding network impedance measurement
2.5 Impulse impedance [Zp]
Grounding system should provide low earth impedance and not simplified low earth
resistance. FFT spectral analyse of lightning impulse shows presence of both high and
low frequency components in the typical lightning waveform. The high frequency is
associated with the extremely fast rising “front” of the lightning impulse while the lower
frequency component resides in the long - high energy - “tail”.
The transient performance of an earthing system is determining of the system ability to
discharge transient energy into the ground and minimizing earth potential rise and
ensuring that equipment and personnel are safe.
The grounding system appears to the lightning impulse as a transmission line. The soil
acts as a dielectric which under high potential stress at the electrode-soil junction can
actually break-down, decreasing the resistivity of the soil during the surge.
Measurement of earth resistance with low frequencies may not provide results which
are indicative of the ground response to a lightning discharge. In complex installations,
many earths are interconnected and the whole network is measured as one.
Lightning first strokes normally have 1 to 10 μs impulse current rise times. Higher dI/dt
occurs with re-strikes which occur in 75% of lightning discharges, which could have 0.2
μs rise time. Under this condition, the local earth is subject to the full discharge current
before the lightening wave-front has travelled more than 60 metres. This assumes
transmission at the speed of light (3•10
capacitance is considered.
The impulse impedance of an earthing system is a useful parameter, to predict the
behaviour in transient conditions (lightning strike for example), as it provides a direct
relationship between the peak potential and peak current rise.
The impulse impedance (Zp) is defined with the ratio between peak voltage and the
peak current.
8
m/s). The speed is lower if inductance and
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Power Network Application Trainer – Earthing / Grounding network impedance measurement
Figure 46-2: Impulse Measurement example
Notes:
The three-wire method is used for impulse impedance measurement.
During the measurement a current impulse (10/350 μs) is injected into the earth
through a shielded auxiliary probe (H).
Figure 47-2: Typical Impulse shape short-circuit
Impedance of probe H should be as low as possible (to inject higher test current),
Voltage peak is measured between probe S and E,
Use short test lead E, to minimize its influence in the final result,
The current probe resistance Rc and potential probe resistance Rp are measured
using 3-Pole measurement at a fix frequency 3.29 kHz @ 40 Vac open-terminal
test voltage.
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Power Network Application Trainer – Earthing / Grounding network impedance measurement
Example:
Influence of inductive impedance part to the test object measured with impulse
impedance measurement and 3-pole measurement method.
Screenshot for Re1 Screenshot for Re2
Screenshot for Re3 Screenshot for Re4
Figure 48-2: Influence of inductive impedance part at impulse measurement
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Power Network Application Trainer – Earthing / Grounding network impedance measurement
Figure 49-2: Influence of inductive impedance part at 3-pole measurement
From this example it is visible, that increased impedance during voltage strike could
cause significant problems, if earthing system is not properly done and serious hazard
to people or equipment.
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Power Network Application Trainer – Earthing / Grounding network impedance measurement
3 Earth Potential
Correct earthing of exposed conductive parts of the object assures that the voltage on
them stays below dangerous level in case of a fault (short-circuit current, lightning
strike). If fault happens a short-circuit current will flow through the object and equipment
into the earthing electrode. The earth resistance is non-zero, so current injected into the
earth at the grounding electrode produces a potential rise related to a distant reference
point.
Earth resistance is not concentrated in one point but it is distributed around whole
electrode. If a faulty current flow through the earth electrode, then a typical distribution
of the voltage occurs around it (voltage funnel). Maximum voltage drop is concentrated
around the earth electrode.
A typical voltage distribution occurs around the electrode, so called “voltage funnel”.
Fault currents close to power distribution objects (substations, distribution towers,
plants) could be very high, up to 200 kA. This can result in dangerous step and contact
voltages. If there are underground metal connections (intended or unknown) the voltage
funnel can get atypical forms and high voltages can occur far from the point of failure.
Therefore, the voltage distribution in case of a fault around these objects should be
carefully analysed.
Figure 50-2: Dangerous voltages on a faulty earthing system
where:
US…. Step Voltage in case of a fault current
UC.... Contact or Touch Voltage in case of a fault current
UF .... Fault voltage
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Power Network Application Trainer – Earthing / Grounding network impedance measurement
Fault duration
(s)
Permissible body
current IB
(mA)
Permissible touch
voltage UTp
(V)
0,05
900
716
0,10
750
654
0,20
600
537
0,50
200
220
1,00
80
117
2,00
60
96
5,00
51
86
10,00
50
85
Maximum allowed time / touch voltage / body current relations, according to EN
50522:2011 standard:
Table 11-2: Permissible body current IB and calculated values of the permissible touch voltage UTp
depending on the fault duration t
f
3.1 Ground Potential Rise, Step Voltage, Contact Voltage
3.1.1 Ground Potential Rise
Ground potential rise (GPR) is defined according the IEEE Std 81-2012 as the
maximum electrical potential that a ground electrode (grid, system etc) could achieve
related to a distant grounding point (potential of remote earth).
Under normal conditions, the grounded electrical equipment operates at near zero
ground potential. In case of ground fault part of fault current flows through earthing
system into the earth and causes the rise of the grid potential related to remote earth.
Analyse of ground potential rise is important in the design phase of electrical
substations because the high potential may be a hazard to people or equipment.
Potential gradient (voltage change over distance) may be so high that a person could be
injured due to the voltage between two feet’s (Step voltage) or between the ground on
which the person is standing and a metal object (Contact voltage).
In case, that there is other infrastructure located close to substation (under ground or
above ground such as: telephone wires, rails, fences, water supply…), could also be
energized because of ground potential in the substation. This transferred potential could
be also hazard to people and equipment outside the substation (many hundreds of
meters away from the fault location). Many factors determine the level of hazard: level
of fault current, soil type (specific resistance, which relates to the actual weather
conditions like moisture and temperature) and protection time to interrupt a fault
(standard value is 330 ms).
Ground potential rise measurements are supported in Metrel instruments MI3290 and
MI3295S & MI3295M using 3 – pole wiring method.
MI3290 Earth Analyzer: Current generator and volt-meter in one instrument: 40V AC, up
to 220mA, 55 to 329 Hz; 0.0 mV … 49.99 V
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Power Network Application Trainer – Earthing / Grounding network impedance measurement
MI3290 is intended to perform measurements on smaller test objects (transformer
pylons, communication towers…). Instrument is battery operated and it is suitable for
objects, where power supply is not available.
MI3295S – Current generator station unit; 55 A max, test voltage < 55 V, 55 Hz. Station
unit is powered by 230V, 50 / 60 Hz
MI3295M – volt-meter measuring unit; 0.01 … 19.99 mV
20.0 … 199.9 mV
200 … 1999 mV
2.00 … 19.99 V
20.0 V … 59.9 V
MI3295 is intended to perform measurements on bigger test objects (power stations,
substation)
Figure 51-2: Example of ground potential measurement
Notes:
AC test current Ie is injected through the test probe H (frequency range: 55 Hz …
329 kHz)
Impedance of probe H should be as low as possible (to inject higher test current),
Voltage drop is measured between probe S and E,
Figure 52-2: Potential gradient measurements example (straight line)
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Power Network Application Trainer – Earthing / Grounding network impedance measurement
3.1.2 Step & contact voltage measurement
At critical locations, like transmission towers, the fence around substation… hazardous
step and contact voltages can occur, which can be life-threatening to living beings.
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Power Network Application Trainer – Earthing / Grounding network impedance measurement
Step voltage is defined as the difference in surface potential that could be achieved by
a person bridging distance of 1 meter with the feet without contacting any grounded
object
The measurement is performed between two ground points at a distance of 1 m. For
performing the test, two step voltage plates where operator stands during measurement
or two 25 kg measuring probes (feet simulation) should be used. The voltage between
the probes is measured by a voltmeter with an internal resistance of 1 kΩ that simulates
the body resistance.
Figure 53-2: Test step/contact voltage plates and 25kg probes
Note: The surface of step (S2053) /voltage (A1353) contact probes is around 200 cm
Figure 54-2: Step voltage measurement with MI3290 instrument
2
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Power Network Application Trainer – Earthing / Grounding network impedance measurement
Figure 55-2: Step voltage measurement with MI3295S & MI3295M instruments
Contact voltage is defined as potential difference between the ground potentialof a
grounding system- the surface potential where a person could stand while at the same
time having a handin contact with a grounded structure or object.
The measurement of contact voltage is performed between an earthed accessible metal
part and ground 1 meter apart from the tested object. The voltage between the probes
is measured by a voltmeter with an internal resistance of 1 kΩ that simulates the body
resistance (test step/contact voltage plates or 25kg probes should be used).
Figure 56-2: Contact voltage measurement with MI3290 instrument
Figure 57-2: Contact voltage measurement with MI3295S & MI3295M instruments
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Power Network Application Trainer – Earthing / Grounding network impedance measurement
4 Exercises on MI 3298 P1 training module
Purpose of the training module is to train different measurement techniques and through
the simulation of different fault conditions understand the nature of the tested object on
the field.
Figure 58-2: Set of Metrel instruments used with MI 3298 P1 training module
With the MI 3298 P1 training module it is possible to perform different earth/impedance
measurements methods as well as simulation of different conditions on the pylon, which
helps to understand different conditions on the real field.
This chapter describes basic principles of measuring methods for measuring:
Earth resistance/impedance,
Impulse impedance,
Pylon Ground Wire test
Step voltage,
Contact voltage,
Ground Potential Rise
Figure 59-2: Available measurement on the MI 3290 Earth Analayser
Note: position of test probes is related to the training module dimension. For more
information about positioning test probes in the real field, please check the examples
under AD 2 – Power Training field and AD 3 – Field measurements.
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Power Network Application Trainer – Earthing / Grounding network impedance measurement
Exercise
Exercise
number
Switch
Positions
Method used
Condition Simulation /
Measuring instrument
Expected result
Pylon earth
resistance
measurement
Item 4.1.1
Regular measurement place
condition (simulated resistive earth
character), single frequency
measurement for 3P method
MI 3290:
3 Pole measurement method:
Ze = 2,56 Ω @ 329 Hz, single mode
Note:
Before, during and after performing tests, follow the instructions for safety work!
Before each measurement check Visual precautions need to be taken before,
during and after performed tests!
Selected measurement methods allow the measurement to be carried out without
disconnecting the grounding system (not allowed for the system under operation).
Disconnecting of grounding system on the object under operation is extremely critical
issue, since it could come to serious fault condition during measurements.
Instrument used: MI 3290 Earth Analyser
MI 3295S Step Contact Voltage Measuring System
MI 3295M
MI 3123
Note:
Take care by using MI 3295S instrument. Connect the current probes according
the instructions in this manual. Wrong connection of current probes could
damage the module or burn the fuse.
Explanation of switch positions (example):
For more details, please check Item 1.8.1.
Table 12-2: Exercises – Earth resistance measurements
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Power Network Application Trainer – Earthing / Grounding network impedance measurement
Single and sweep frequency
measurement /
MI 3290
4 Pole measurement method:
Ze = 2.55 Ω @ 329 Hz, single mode
Ze = 2.55 Ω @ sweep mode (329 Hz)
MI 3213
MI 3213:
4 Pole measurement method
Ze = 2,66 Ω @ 125 Hz
MI 3295S
MI 3295S:
4 Pole measurement method
Ze = 2,94 Ω @ 55 Hz
Item 4.1.2
Regular measurement place
condition (simulated inductive earth
character), single and frequency
measurement /
MI 3290
Ze = 3,32Ω @ 329 Hz, single mode
Ze = 3,31Ω@ sweep mode (329 Hz)
Simulated broken foot Nm. 2 & 3
connection (simulated resistive earth
character), single frequency
measurements /
MI 3290
Ze = 3,94Ω @ 329 Hz, single mode
Regular measurement place
condition (simulated resistance
/inductive earth character), simulated
ground wire connection/
MI 3290
Ze = 1.46 Ω @ 4-Pole at 329 Hz, R type
Ze = 1.48 Ω @ 4-Pole at 329 kHz, L type
Item 4.1.3
Regular measurement place
condition (simulated resistive earth
character), flex measurement – one
flex clamp /single foot
MI 3290
Foot Nm. 1 approx. 22,4 Ω @ 329 Hz
Foot Nm. 2 approx. 10,9 Ω @ 329 Hz
Foot Nm. 3 approx. 22,1 Ω @ 329 Hz
Foot Nm. 4 approx. 5,47 Ω @ 329 Hz
Ztot calc = 2,74 Ω
Simulated broken foot Nm. 2 & 3
connection (simulated resistive earth
character), flex measurement – one
flex clamp / single foot
MI 3290
Foot Nm. 1 approx. 17,8 Ω @ 329 Hz
Foot Nm. 2 approx. 391 Ω @ 329 Hz
Foot Nm. 3 approx. 283 Ω @ 329 Hz
Foot Nm. 4 approx. 5,33 Ω @ 329 Hz
Ztot calc = 3,99 Ω
Regular measurement place
condition (simulated resistive earth
character), flex measurement,
simulated ground wire connection /
single foot
MI 3290
Foot Nm. 1 approx. 30,1 Ω @ 329 Hz
Foot Nm. 2 approx. 11,7 Ω @ 329 Hz
Foot Nm. 3 approx. 23,6 Ω @ 329 Hz
Foot Nm. 4 approx. 5,63 Ω @ 329 Hz
Ztot calc = 2,95 Ω
Regular measurement place
condition (simulated resistive earth
character), flex measurement,
simulated ground wire connection /
single foot
MI 3290
Foot Nm. 1 approx. 47,2 Ω @ 329 Hz
Foot Nm. 2 approx. 16,1 Ω @ 329 Hz
Foot Nm. 3 approx. 30,3 Ω @ 329 Hz
Foot Nm. 4 approx. 7,25 Ω @ 329 Hz
Ztot calc = 3,93 Ω
Regular measurement place
condition (simulated resistive earth
character), flex measurement,
simulated ground wire connection /
two foots measured together
MI 3290
Foot Nm. 1 & 2 approx. 6,27 Ω @ 329 Hz
Foot Nm. 3 & 4 approx. 4,61 Ω @ 329 Hz
Ztot calc = 2,65 Ω
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Power Network Application Trainer – Earthing / Grounding network impedance measurement
Regular measurement place
condition (simulated resistive earth
character), flex measurement,
simulated ground wire connection /
all four foots measured together
MI 3290
Ztot = 2,65 Ω @ 329 Hz
Item 4.1.4
Regular measurement place
condition (simulated resistive earth
character), flex measurement,
simulated ground wire connection /
MI 3290
Ig_w< 0,10 mA
Regular measurement place
condition (simulated resistance earth
character), simulated ground wire
connection/
MI 3290
Ig_w=28,7 mA
Item 4.1.5
Regular measurement place
condition (simulated resistance earth
character), simulated ground wire
connection/
MI 3290
Re = 2,7 Ω @ at 25 kHz, R type
Regular measurement place
condition (simulated inductive earth
character), simulated ground wire
connection/
MI 3290
Re = 6.2 Ω @ at 25 kHz, L type
Item 4.1.6
Regular measurement place
condition (simulated inductive earth
character), single and frequency
measurement /
MI 3290
S-Flex:
Ztot = 2,66 Ω @ 329 Hz
4-pole:
Ze = 2,68 Ω @ 329 Hz
Simulated broken foot Nm. 2 & 3
connection (simulated inductive earth
character), simulated ground wire
connection /
MI 3290
4-pole:
Ze = 1,78 Ω @ 329 Hz
HF:
Re = 6,7Ω @ 25kHz
S-Flex:
Foot Nm. 1 approx. 14,76 Ω @ 329 Hz
Foot Nm. 2 approx. 348 Ω @ 329 Hz
Foot Nm. 3 approx. 1,767 kΩ@ 329 Hz
Foot Nm. 4 approx. 6,62 Ω @ 329 Hz
Z
tot calc
= 4,49 Ω
Item 4.1.7
Regular measurement place
condition (simulated resistive earth
character)/
MI 3290
Zp = 3,7 Ω
Regular measurement place
condition (simulated inductive earth
character)/
MI 3290
Zp = 112 Ω
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Power Network Application Trainer – Earthing / Grounding network impedance measurement
Regular measurement place
condition (simulated resistive earth
character), simulated ground wire
connection/
MI 3290
Zp= 3,7 Ω
Regular measurement place
condition (simulated inductive earth
character), simulated ground wire
connection/
MI 3290
Zp= 74 Ω
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Power Network Application Trainer – Earthing / Grounding network impedance measurement
Exercise
Exercise
number
Switch
Positions
Method used
Condition Simulation /
Measuring instrument
Expected result
Step / Contact voltage
Item 4.2.1
Step voltage measurement
/
MI3290 + MI3295M
Result depends on the position of
test probes
Item 4.2.2
Step voltage measurement
/
MI3295S + MI3295M
Result depends on the position of
test probes
Item 4.2.3
Contact voltage measurement
/
MI3290 + MI3295M
Result depends on the position of
test probes
Item 4.2.4
Contact voltage measurement
/
MI3295S + MI3295M
Result depends on the position of
test probes
GPR
Item 4.3.1
GPR straight line measurement
/
MI3290
Note: MI3290 is used as current
generator and volt-meter
Result depends on the position of
test probes
Item 4.3.2
GPR straight line measurement
/
MI3290& MI3295M
Note:
MI3290 is used as current generator
MI3295M is used as volt-meter
Result depends on the position of
test probes
Item 4.3.3
GPR straight line measurement
/
MI3295S & MI3295M
Note:
MI3290S is used as current generator
MI3295M is used as volt-meter
Result depends on the position of
test probes
Table 13-2: Exercises – GPR & Step/Contact measurements
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Power Network Application Trainer – Earthing / Grounding network impedance measurement
Switch position
Simulated condition
Application
Expected result
Regular measurement place
condition (simulated resistive earth
character), single frequency
measurement
Industrial areas
Transformer stations
Radio towers
Pylons ground wire connection
Solar power plants
Wind & water turbine
Ze = 2,56 Ω @ 329 Hz
4.1 Earth resistance measurement exercises
4.1.1 3-Pole and 4-Pole earth resistance measuring method
4.1.1.1 Measurement with MI 3290 Earth Analyzer
4.1.1.1.1 3 Pole measuring method
Figure 60-2: 3-pole earth resistance measurement with MI 3290
Exercise is used to practice impedance measurement of single pylon installation without
connected ground wire.
3-pole method uses three-wire connection, with the possibility of frequency selection
from 55 Hz to 15 kHz (fixed / sweep mode). In this exercise, fixed frequency
measurement is used (329 Hz).
Table 14-2: Measurement setup/result for 3-pole measurement method
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Power Network Application Trainer – Earthing / Grounding network impedance measurement
Measuring procedure
1. Select proper switch position on the training module.
2. Under Earth test function select the 3P measurement method
3. Connect measuring cables according the connection diagram. Press icon to
enter into HELP menu!
- connect the black test probe to H (C1) & GUARD terminal and other part
to the “current probe” RCE
- connect the blue test probe to E(C2) terminal and other part to the pylon
- connect the green test probe to the S (P1) terminal and other part to the
“voltage probe” RP
4. Set the parameters by clicking the bottom left dark grey corner.
Since exercises on the training module are used only for training purposes distance to
current (R) and voltage (r) probes is not needed. Select “Single test mode “and 329 Hz
test frequency.
5. Start the measurement by pressing START key on the instrument or icon
on the LCD
Expected result for 3-Pole method:
Since limit value was not set, there is no PASS/FAIL indication. Use the proper limit
value if you need to evaluate the result.
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Power Network Application Trainer – Earthing / Grounding network impedance measurement
Expected result for 3-Pole method:
Simulated resistance of current and voltage probe was around 496 Ω, so the injected
current into the system was quite low; approx. 61 mA.
Presented earth impedance and earth resistance are the same, since selected load
character is the resistance type.
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Power Network Application Trainer – Earthing / Grounding network impedance measurement
Switch position
Simulated condition
Application
Expected result
Regular measurement place
condition (simulated resistive earth
character), single and sweep
frequency measurement
Industrial areas
Transformer stations
Radio towers
Pylons without ground wire
connection
Solar power plants
Wind &water turbine
Ze = 2.55 Ω @ 329 Hz, single mode
Ze = 2.55 Ω @ sweep mode (329 Hz)
4.1.1.1.2 4 Pole measuring method
Figure 61-2: 4-pole earth resistance measurement with MI 3290
4-pole method uses four-wire connection, so the resistance of test cables is excluded
from the measurement result. It is possible to select the measurement frequency
selection from 55 Hz to 15 kHz (fixed / sweep mode). In this exercise fixed frequency
measurement is used (329 Hz) in first step and frequency sweep in the second one.
Table 15-2: Measurement setup/result for 3-pole measurement method
Measuring procedure – single frequency measurement:
1. Select proper switch position on the training module.
2. Under Earth test function select the 4P measurement method
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Power Network Application Trainer – Earthing / Grounding network impedance measurement
3. Connection is similar to 3 Pole method connection. Only additional connection of ES
(P2) terminal is needed.
- connect the red test probe to ES(P2) terminal and other part to the pylon
4. Set the parameters by clicking the bottom left dark grey corner – single mode at 329
Hz
Since exercises on the puzzle uses only for training purposes distance to current (R)
and voltage (r) probes is not needed. Select “Single test mode “and 329 Hz test
frequency
5. Start the measurement by pressing START key on the instrument or icon
on the LCD
Expected result:
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Power Network Application Trainer – Earthing / Grounding network impedance measurement
Since limit value was not set, there is no PASS/FAIL indication. Use the proper limit
value if you need to evaluate the result.
Comparing result to 3 Pole method, there is practicaly no difference.
Measuring procedure – sweep frequency measurement:
Same measurement could be repeated usingsweep mode, frequencies in the range
from 55 Hz to 15 kHz.
Parameter setup:
Expected result:
Impedance measurement in whole frequency range shows resistance character,
practically no change in the frequency range from 55 Hz to 15 kHz
If there is status on the LCD, which shows, that there is high impedance to earth
probes detected.
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Power Network Application Trainer – Earthing / Grounding network impedance measurement
Switch position
Simulated condition
Application
Expected result
Regular measurement place
condition (simulated resistive earth
character), single and sweep
frequency measurement
Residential areas
Radio towers
Pylons without ground wire
connection
Solar power plants
Wind & water turbine
Re = 2.66Ω @ 125 Hz
4.1.1.2 Measurement with MI 3123 SmartTEC (Earth/Clamp) meter
Figure 62-2: Earth measurement with MI 3123
MI 3123 use 4 wire measurement method for the earth resistance measurement, so the
resistance of test cables is excluded from the measurement result.
Measurement is done at fix frequency 125 Hz.
Table 16-2: Measurement setup/result for 4-wire measurement method with MI 3123
Measuring procedure:
1. Select proper switch position on the training module.
2. By using function selection keys (Left & Right) select EARTH measurement function
and with navigation buttons (Up & Down) select EARTH RE function.
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Power Network Application Trainer – Earthing / Grounding network impedance measurement
3. Press HELP button to check the connection diagram.
- connect the black test probe to H terminal and other part to the “current
probe” RCE
- connect the blue test probe to E terminal and the red one to ES terminal
and other parts to the pylon
- connect the green test probe to the S terminal and other part to the
“voltage probe” RP
4. Select limit value to evaluate the measured result. To enter into the “limit window”
press TAB button and select the limit by using Up & Down navigation buttons. In this
case, limit value 2 Ω is used.
5. Start the measurement by pressing TEST key.
Expected result:
Measured eath resistance is 2.66 Ω, which h is less than setup limit 3 Ω, so there is
PASS indication on the LCD screen.
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Power Network Application Trainer – Earthing / Grounding network impedance measurement
Switch position
Simulated condition
Application
Expected result
Regular measurement place
condition (simulated resistive earth
character), single and sweep
frequency measurement
Radio towers
Pylons without ground wire
connection
Solar power plants
Wind & water turbine
Power transmission
Power distribution
Re = 2,94Ω @ 55 Hz
4.1.1.3 Measurement with MI 3295S Step Contact Voltage Measuring System
Figure 63-2: Earth measurement with MI 3295S
This exercise will present the usage of MI 3295S measuring system for earth resistance
measurement. Four wire earth resistance measurement method is supported.
Measurement is done at fix frequency 55 Hz. MI 3295S device needs external 230V AC
power supply and it is intended for measurement of bigger systems, where higher test
current needs to be generated. Test current up to 7.5 A could be generated and test
voltage up to 50 V.
Table 17-2: Measurement setup/result for 4-wire measurement method with MI 3295S
Measuring procedure:
1. Select proper switch position on the training module.
2. By using function selection keys (Left & Right) select EARTH measurement function
and with navigation buttons (Up & Down) select EARTH RE function.
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Power Network Application Trainer – Earthing / Grounding network impedance measurement
3. Press HELP button to check the connection diagram.
- connect the C2/E current test lead and ES potential lead to the pylon
- connect C1/H test lead to “current probe” RCE
- connect the S potential probe to the “voltage probe” RP
4. Start the measurement by pressing TEST key.
Expected result:
Note: High resistance of current and voltage probes are detected!
Summary:
Presented exercise shows the usage of three different METREL instrument (MI 3290,
MI 3123 and MI 3295S) for measuring earth resistance usig 3 Pole and 4 Pole
measuring method. Measurement selection and method selection depends on the
object size and surrounding.
Earth Analyzer MI 3290 supports different measurement methods as well as
measurements could be performed at different frequences, so deeper analyze (not only
simple measiurement) of the object’s earth resistance could be done and it is battery
operated.
All measurements performed with different instruments on the test object (training
module) give comparable results.
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Power Network Application Trainer – Earthing / Grounding network impedance measurement
3 – Pole / 329 Hz/ MI 3290
2,56 Ω
4 – Pole / 329 Hz/ MI 3290
2,55 Ω
4 – Pole / 125 Hz/ MI 3213
2,66 Ω
4 – Pole / 55 Hz/ MI 3295S
2,94 Ω
Results comparison:
Table 18-2: Result comparison for 3-pole and 4-pole measurement done with different instruments
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Power Network Application Trainer – Earthing / Grounding network impedance measurement
Switch position
Simulated condition
Application
Expected result
Regular measurement place
condition (simulated inductive
earth character), single and
sweep frequency
measurement
Industrial areas
Transformer stations
Radio towers
Pylons without ground wire
connection
Solar power plants
Wind &water turbine
Ze = 3,32Ω @ 329 Hz, single mode
Ze = 3,31Ω@ sweep mode
4.1.2 4 Pole measuring method – simulated different test object state
4.1.2.1 Simulation of inductive earth character, regular pylon
foot’s condition
Figure 64-2: 4-pole earth measurements setup with MI 3290
Table 19-2: Measurement setup/result for 4-pole method
Measurement setup and procedure is the same as under exercise Nm. 1 (Item
4.1.1.1.2), so check the details for proper connection.
Select proper switch position on the training module.
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Power Network Application Trainer – Earthing / Grounding network impedance measurement
Measurement at fixed frequency 329 Hz:
Expected result for single frequency measurement:
Since there is additional inductive part added to the earth resistance, earth impedance
is higher than the result measured in exercise Nm.1, item 4.1.1.1.2.
Measuring procedure – sweep frequency measurement:
Measurement setup and procedure is the same as under exercise Nm. 1 (Item
4.1.1.1.2), so check the details for proper connection.
Expected result:
Earth impedance measurement in frequency range from 55 Hz up to 15.4 kHz shows
prominent inductive character of measured object.
We propose to use “sweep mode” measurement for analysing the earth impedance
character, to see the test object characteristic also at the higher frequencies.
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Power Network Application Trainer – Earthing / Grounding network impedance measurement
Switch position
Simulated condition
Application
Expected result
Simulated broken foot Nm. 2
& 3 connection (simulated
resistive earth character),
single frequency
measurements
Industrial areas
Transformer stations
Radio towers
Pylons without ground wire
connection
Solar power plants
Wind & water turbine
Ze = 3,94Ω @ 329 Hz, single mode
4.1.2.2 Simulation of resistance earth character and broken pylon’s foot connection
Figure 65-2: 4-pole earth measurements setup with MI 3290
Table 20-2: Measurement setup/result for 4-pole method with simulated error
Measuring procedure:
Select proper switch position on the training module.
Measurement setup and procedure is the same as under exercise Nm. 1 (Item
4.1.1.1.2), so check the details for proper connection and select proper position of
selected switches on the training module.
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Power Network Application Trainer – Earthing / Grounding network impedance measurement
Expected result:
Comparing the result measured with exercise under Nm.1 (Item 4.1.1.1.2) – 2,55 Ω vs
3,94 Ω:
- There is no big (critical) difference between the both values (in case, that
value of 3,94 Ω is too high for the selected object)
- Measurement with S-Flex method will show us, that result 3,94 Ω is not
acceptable due to the broken foot’s connection. Four pole measurement
method does not show us the separate foot condition, so differen
measurement method should be choosen.
4.1.2.3 Simulation of resistance/inductive earth character, regular foot’s condition and simulated Ground Wire connection
Figure 66-2: 4-pole earth measurements setup with MI 3290
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Power Network Application Trainer – Earthing / Grounding network impedance measurement
Switch position
Simulated condition
Application
Expected result
Regular measurement place
condition (simulated
resistance /inductive earth
character), simulated ground
wire connection
Industrial areas
Transformer stations
Radio towers
Pylons without ground wire
connection
Solar power plants
Wind & water turbine
Ze = 1.46 Ω @ 4-Pole at 329 Hz, R type
Ze = 1.48 Ω @ 4-Pole at 329 kHz, L type
Pylons are connected together via Ground Wire which cause that the part of the current
is completed via the ground wire link and results measured with the 4-Pole method are
not correct and different measurement method should be selected.
Table 21-2: Measurement setup/result for 4-pole method with different test object condition
Measuring procedure – resistance earth character
Select proper switch position on the training module:
Measurement setup and procedure is the same as under exercise Nm. 1 (Item
4.1.1.1.2), so check the details for proper connection.
Expected result:
Select proper switch position on the training module:
Expected result:
Both results are quite close to each other, but significantly smaller compared to case,
where ground wire is not connected.
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Power Network Application Trainer – Earthing / Grounding network impedance measurement
4 – Pole / 329 Hz
3,32 Ω
3,94 Ω
1,46 Ω
1,48 Ω
Since there is simulation of ground wire connection also “impedance of neighbourhood
pylons is included” (in our case simulated inductance connected to the earth). From the
results, we can see, that the 4-Pole method is not proper one for measuring pylons
earth impedance connected via ground wire.
Result comparison:
Table 22-2: Result comparison: same test method vs different test object setup
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Power Network Application Trainer – Earthing / Grounding network impedance measurement
Switch position
Simulated condition
Application
Expected result
Regular measurement place
condition (simulated resistive earth
character), one flex clamp
Pylons (mono and multi-leg)
with and without protective earth
cable connection
Ski lifts
Radio towers
Foot Nm. 1 approx. 22,4 Ω
Foot Nm. 2 approx. 10,9 Ω
Foot Nm. 3 approx. 22,1 Ω
Foot Nm. 4 approx. 5,47 Ω
Z
tot calc
= 2,74 Ω
4.1.3 S – Flex measuring method by using one Flex-clamp
4.1.3.1 S – Flex measuring method by using one Flex- clamp with simulated regular pylon’s foot condition and resistance earth character
Figure 67-2: S-Flex measurement setup with MI 3290
This exercise presents procedure how to perform complete earth measurement on the
transmission pylon with four foots with only one flex clamp.
Table 23-2: S-Flex measurement setup/result
Measuring procedure
1. Select proper switch position on the training module:
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Power Network Application Trainer – Earthing / Grounding network impedance measurement
2. Under Earth test function select the S-Flex measurement method
3. Connect the flex – clamp around the first pylon foot and measuring cables according
the connection diagram.
- connect the black test probe to H (C1) & GUARD terminal and other part
to the “current probe” RCE
- connect the red and blue test probe to E(C2) terminal and other part to the
pylon
- connect the green test probe to the S (P1) terminal and other part to the
“voltage probe” RP
- Fit the flex clamp around the first pylon foot.
4. Set the parameters by clicking the bottom left dark grey corner.
Single measurement at test frequency 329 Hz is selected.
Number of turns should correspond to the actual state; limit value is not set.
5. Start the measurement by pressing START key on the instrument or icon
on the LCD
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Power Network Application Trainer – Earthing / Grounding network impedance measurement
Expected result for foot number 1:
Generated current is quite low due to high current probe resistance (61,5 mA).
Since limit value was not set, there is no PASS/FAIL indication. Use the proper limit
value if you need to evaluate the result.
Since this measurement gives result only for the single foot, measurement needs to be
repeated also on the other foots.
Move the clamp to the next foot (sequential to foot 2, 3 and 4) and repeat the
measurement.
Expected result for foot number 2:
Expected result for foot number 3:
Expected result for foot number 4:
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