GE 6000 User Manual
GE Consumer & Industrial
ISO9001:2000
Multilin
EPM 6000 Multi-function Power
Metering System
Chapter 1:
EPM 6000
Instruction Manual
Software Revision: 4.5
Manual P/N: 1601-0215-A4
Manual Order Code: GEK-106558C
Copyright © 2007 GE Multilin
GE Multilin
215 Anderson Avenue, Markham, Ontario
Canada L6E 1B3
Tel: (905) 294-6222 Fax: (905) 201-2098
Internet:
*1601-0215-A4*
http://www.GEmultilin.com
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GE Multilin's Quality
Management System is
registered to ISO9001:2000
QMI # 005094
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Table of Contents
1: OVERVIEW INTRODUCTION ................................................................................................................................ 1-1
D
ESCRIPTION ........................................................................................................................ 1-1
H
IGHLIGHTS ......................................................................................................................... 1-1
FEATURES ............................................................................................................................................ 1-3
U
NIVERSAL VOLTAGE INPUTS ............................................................................................ 1-3
C
URRENT INPUTS ................................................................................................................. 1-3
U
TILITY PEAK DEMAND .......................................................................................................1-3
M
EASURED VALUES ............................................................................................................ 1-4
ORDERING ........................................................................................................................................... 1-5
O
RDER CODES ..................................................................................................................... 1-5
SPECIFICATIONS ............................................................................................................................... 1-6
I
NPUTS/OUTPUTS ................................................................................................................ 1-6
M
ETERING ............................................................................................................................. 1-6
E
NVIRONMENTAL ................................................................................................................. 1-7
C
OMMUNICATIONS .............................................................................................................. 1-7
M
ECHANICAL PARAMETERS ................................................................................................ 1-7
A
PPROVALS ........................................................................................................................... 1-8
2: ELECTRICAL
BACKGROUND
THREE-PHASE POWER MEASUREMENT .................................................................................2-1
ESCRIPTION ........................................................................................................................ 2-1
D
THREE-PHASE SYSTEM CONFIGURATIONS ........................................................................... 2-2
D
ESCRIPTION ........................................................................................................................ 2-2
W
YE CONNECTION .............................................................................................................. 2-2
D
ELTA CONNECTION ........................................................................................................... 2-4
B
LONDELL'S THEOREM AND THREE-PHASE MEASUREMENT ........................................2-5
POWER, ENERGY, AND DEMAND .............................................................................................. 2-8
D
ESCRIPTION ........................................................................................................................ 2-8
P
OWER .................................................................................................................................. 2-8
E
NERGY ................................................................................................................................. 2-8
D
EMAND ...............................................................................................................................2-10
REACTIVE ENERGY AND POWER FACTOR ............................................................................. 2-12
R
EAL, REACTIVE, AND APPARENT POWER ........................................................................ 2-12
P
OWER FACTOR ................................................................................................................... 2-13
HARMONIC DISTORTION ..............................................................................................................2-14
H
ARMONICS OF A NON-SINUSOIDAL WAVEFORM ......................................................... 2-14
I
NDUCTIVE AND CAPACITIVE IMPEDANCE ......................................................................... 2-15
V
OLTAGE AND CURRENT MONITORING ............................................................................ 2-15
W
AVEFORM CAPTURE .........................................................................................................2-16
POWER QUALITY .............................................................................................................................. 2-17
D
ESCRIPTION ........................................................................................................................ 2-17
3: INSTALLATION MECHANICAL INSTALLATION .....................................................................................................3-1
IMENSIONS ......................................................................................................................... 3-1
D
ANSI I
NSTALLATION STEPS ............................................................................................... 3-2
DIN I
NSTALLATION STEPS .................................................................................................. 3-3
ELECTRICAL INSTALLATION ......................................................................................................... 3-5
EPM 6000 MULTI-FUNCTION POWER METERING SYSTEM – USER GUIDE TOC–1
INSTALLATION CONSIDERATIONS ....................................................................................... 3-5
CT L
EADS TERMINATED TO METER ...................................................................................3-6
CT L
EADS PASS-THROUGH (NO METER TERMINATION) ................................................ 3-6
Q
UICK CONNECT CRIMP CT TERMINATIONS ................................................................... 3-7
V
OLTAGE AND POWER SUPPLY CONNECTIONS .............................................................. 3-7
G
ROUND CONNECTIONS ....................................................................................................3-8
WIRING DIAGRAMS .........................................................................................................................3-9
D
ESCRIPTION ........................................................................................................................ 3-9
W
YE, 4-WIRE WITH NO PTS AND 3 CTS, 3 ELEMENT ..................................................3-10
W
YE, 4-WIRE WITH NO PTS AND 3 CTS, 2.5 ELEMENT .............................................. 3-11
W
YE, 4-WIRE WITH 3 PTS AND 3 CTS, 3 ELEMENT .................................................... 3-12
W
YE, 4-WIRE WITH 2 PTS AND 3 CTS, 2.5 ELEMENT ................................................. 3-13
D
ELTA, 3-WIRE WITH NO PTS AND 2 CTS ..................................................................... 3-14
D
ELTA, 3-WIRE WITH 2 PTS AND 2 CTS ........................................................................ 3-15
C
URRENT-ONLY MEASUREMENT (THREE-PHASE) .......................................................... 3-16
C
URRENT-ONLY MEASUREMENT (DUAL-PHASE) ............................................................ 3-17
C
URRENT-ONLY MEASUREMENT (SINGLE-PHASE) ......................................................... 3-18
COMMUNICATIONS SETUP .......................................................................................................... 3-19
D
ESCRIPTION ........................................................................................................................ 3-19
I
RDA COM1 PORT .............................................................................................................3-19
RS485 COM2 P
ORT ......................................................................................................... 3-19
4: USING THE METER FRONT PANEL INTERFACE ............................................................................................................ 4-1
ESCRIPTION ........................................................................................................................ 4-1
D
F
ACEPLATE ELEMENTS ........................................................................................................ 4-1
F
ACEPLATE BUTTONS .......................................................................................................... 4-2
P
ERCENTAGE OF LOAD BAR ...............................................................................................4-3
W
ATT-HOUR ACCURACY TESTING (VERIFICATION) ........................................................ 4-4
CONFIGURING THE METER VIA THE FRONT PANEL .......................................................... 4-5
O
VERVIEW ............................................................................................................................ 4-5
S
TART UP .............................................................................................................................. 4-5
M
AIN MENU ......................................................................................................................... 4-6
R
ESET MODE AND PASSWORD ENTRY .............................................................................4-6
CHANGING SETTINGS IN CONFIGURATION MODE ...........................................................4-9
D
ESCRIPTION ........................................................................................................................ 4-9
C
ONFIGURING THE SCROLL FEATURE ............................................................................... 4-9
P
ROGRAMMING THE CONFIGURATION MODE SCREENS ................................................ 4-10
C
ONFIGURING THE CT SETTING ........................................................................................ 4-11
C
ONFIGURING THE PT SETTING ........................................................................................4-12
C
ONFIGURING THE CONNECTION SETTING ...................................................................... 4-13
C
ONFIGURING THE COMMUNICATION PORT SETTING .................................................... 4-14
OPERATING MODE ...........................................................................................................................4-17
D
ESCRIPTION ........................................................................................................................ 4-17
5: COMMUNICATIONS MODBUS COMMUNICATIONS ..................................................................................................... 5-1
EMORY MAP DESCRIPTION ............................................................................................. 5-1
M
M
EMORY MAP ......................................................................................................................5-1
M
ODBUS MEMORY MAP NOTES .......................................................................................5-7
M
ODBUS MEMORY MAP DATA FORMATS ........................................................................5-9
DNP POINT MAPPING ..................................................................................................................... 5-10
DNP P
OINT MAPS ..............................................................................................................5-10
DNP P
OINT MAP NOTES ...................................................................................................5-12
TOC–2 EPM 6000 MULTI-FUNCTION POWER METERING SYSTEM – USER GUIDE
DNP IMPLEMENTATION ................................................................................................................. 5-13
O
VERVIEW ............................................................................................................................ 5-13
D
ATA LINK LAYER ................................................................................................................ 5-13
T
RANSPORT LAYER .............................................................................................................. 5-13
A
PPLICATION LAYER ............................................................................................................5-14
DNP OBJECTS AND VARIATIONS ............................................................................................... 5-15
D
ESCRIPTION ........................................................................................................................ 5-15
B
INARY OUTPUT STATUS (OBJECT 10, VARIATION 2) ...................................................5-15
C
ONTROL RELAY OUTPUT (OBJECT 12, VARIATION 1) .................................................. 5-15
32-B
IT BINARY COUNTER WITHOUT FLAG (OBJECT 20, VARIATION 4) .................... 5-16
16-B
IT ANALOG INPUT WITHOUT FLAG (OBJECT 30, VARIATION 5) ......................... 5-16
C
LASS 0 DATA (OBJECT 60, VARIATION 1) ..................................................................... 5-17
I
NTERNAL INDICATIONS (OBJECT 80, VARIATION 1) ...................................................... 5-17
6: MISCELLANEOUS NAVIGATION MAPS .........................................................................................................................6-1
NTRODUCTION .....................................................................................................................6-1
I
M
AIN MENU SCREENS ........................................................................................................ 6-2
O
PERATING MODE SCREENS ............................................................................................. 6-3
R
ESET MODE SCREENS ....................................................................................................... 6-4
C
ONFIGURATION MODE SCREENS .................................................................................... 6-5
REVISION HISTORY .......................................................................................................................... 6-6
R
ELEASE DATES ...................................................................................................................6-6
C
HANGES TO THE MANUAL ............................................................................................... 6-6
WARRANTY ......................................................................................................................................... 6-8
GE M
ULTILIN WARRANTY .................................................................................................. 6-8
EPM 6000 MULTI-FUNCTION POWER METERING SYSTEM – USER GUIDE TOC–3
TOC–4 EPM 6000 MULTI-FUNCTION POWER METERING SYSTEM – USER GUIDE
GE Consumer & Industrial
Multilin
1.1 Introduction
EPM 6000 Multi-function Power
Metering System
Chapter 1: Overview
Overview
1.1.1 Description
1.1.2 Highlights
The EPM 6000 is a multifunction power meter designed to be used in electrical substations,
panel boards and as a power meter for OEM equipment. The unit provides multifunction
measurement of electrical parameters.
The unit is designed with advanced measurement capabilities, allowing it to achieve high
performance accuracy. The EPM 6000 is specified as a 0.2% class energy meter for billing
applications as well as a highly accurate panel indication meter.
The EPM 6000 provides a host of additional capabilities, including standard RS485 Modbus
Protocol and an IrDA port remote interrogation.
The following EPM 6000 features are detailed in this manual:
• 0.2% class revenue certifiable energy and demand metering
• Meets ANSI C12.20 (0.2%) and IEC 687 (0.2%) classes
• Multifunction measurement including voltage, current, power, frequency, energy
• Percentage of load bar for analog meter perception
• Easy-to-use faceplate programming
• IrDA port for PDA remote read
• RS485 Modbus communications
EPM 6000 MULTI-FUNCTION POWER METERING SYSTEM – USER GUIDE 1–1
FIGURE 1–1: EPM 6000 Highlights
CHAPTER 1: OVERVIEW
1–2 EPM 6000 MULTI-FUNCTION POWER METERING SYSTEM – USER GUIDE
CHAPTER 1: OVERVIEW
1.2 Features
1.2.1 Universal Voltage Inputs
1.2.2 Current Inputs
Voltage Inputs allow measurement to 416 V line-to-neutral and 721 V line-to-line. This
insures proper meter safety when wiring directly to high voltage systems. One unit will
perform to specification on 69 V, 120 V, 230 V, 277 V, and 347 V systems.
The EPM 6000 current inputs use a unique dual input method.
• Method 1 – CT Pass Through: The CT passes directly through the meter without
any physical termination on the meter. This insures that the meter cannot be a
point of failure on the CT circuit. This is preferable for utility users when sharing
relay class CTs. No burden is added to the secondary CT circuit.
• Method 2 – Current “Gills”: This unit additionally provides ultra-rugged
termination pass-through bars that allow CT leads to be terminated on the meter.
This, too, eliminates any possible point of failure at the meter. This is a preferred
technique for insuring that relay class CT integrity is not compromised (the CT will
not open in a fault condition).
FIGURE 1–2: Current Input Connections
1.2.3 Utility Peak Demand
The EPM 6000 provides user-configured Block (fixed) or Rolling window demand. This
feature allows you to set up a customized demand profile. Block window demand is
demand used over a user-defined demand period (usually 5, 15, or 30 minutes). Rolling
window demand is a fixed window demand that moves for a user-specified subinterval
period. For example, a 15-minute demand using 3 subintervals and providing a new
demand reading every 5 minutes, based on the last 15 minutes.
EPM 6000 MULTI-FUNCTION POWER METERING SYSTEM – USER GUIDE 1–3
Utility demand features can be used to calculate kW, kvar, kVA and PF readings. All other
parameters offer maximum and minimum capability over the user-selectable averaging
period. Voltage provides an instantaneous maximum and minimum reading which
displays the highest surge and lowest sag seen by the meter.
1.2.4 Measured Values
The EPM 6000 provides the following measured values all in real time and some
additionally as average, maximum, and minimum values.
Measured Values Real Time Average Maximum Minimum
Voltage L-N XXX
Voltage L-L XXX
Current per phase XXXX
Watts XXXX
CHAPTER 1: OVERVIEW
Table 1–1: EPM 6000 Measured Values
vars XXXX
VA XXXX
Power Factor (PF) XXXX
Positive watt-hours X
Negative watt-hours X
Net watt-hours X
Positive var-hours X
Negative var-hours X
Net var-hours X
VA-hours X
Frequency XXX
%THD XXX
Voltage angles X
Current angles X
% of load bar X
1–4 EPM 6000 MULTI-FUNCTION POWER METERING SYSTEM – USER GUIDE
CHAPTER 1: OVERVIEW
1.3 Ordering
1.3.1 Order Codes
The order codes for the EPM 6000 are indicated below.
Table 1–2: EPM 6000 Order Codes
PL6000 – * – * – *
Base Unit
System
Frequency
Current Input
THD and Pulse Output
For example, to order an EPM 6000 for 60 Hz system with a 1 A secondary CT input and no
THD or pulse output option, select order code PL6000-6-1A-0. The standard unit includes
display, all current/voltage/power/frequency/energy counters, percent load bar, RS485,
and IrDA communication ports.
PL6000 || |
5 | |
6 | |
1A |
5A |
EPM 6000 Power Metering System
50 Hz AC frequency system
60 Hz AC frequency system
1 A secondary CT
5 A secondary CT
No THD or pulse output option
0
THD, limit alarms, and 1 KYZ pulse output
THD
EPM 6000 MULTI-FUNCTION POWER METERING SYSTEM – USER GUIDE 1–5
1.4 Specifications
1.4.1 Inputs/Outputs
CHAPTER 1: OVERVIEW
POWER SUPPLY
Range:..................................................................D2 Option: Universal, 90 to 265 V AC at 50/60Hz, or 100 to
370 V DC
D Option: 18 to 60 V DC
Power consumption:.....................................5 VA, 3.5 W
VOLTAGE INPUTS (MEASUREMENT CATEGORY III)
Range:..................................................................Universal, Auto-ranging up to 416 V AC L-N, 721 V AC L-L
Supported hookups:......................................3-element Wye, 2.5-element Wye, 2-element Delta,
4-wire Delta
Input impedance:...........................................1 MOhm/phase
Burden:................................................................0.0144 VA/phase at 120 Volts
Pickup voltage: ................................................10 V AC
Connection:.......................................................Screw terminal (see Voltage Connection on page 3–8)
Maximum input wire gauge: ....................AWG #12 / 2.5 mm
Fault withstand: ..............................................Meets IEEE C37.90.1
Reading:..............................................................Programmable full-scale to any PT ratio
2
1.4.2 Metering
CURRENT INPUTS
Class 10:..............................................................5 A nominal, 10 A maximum
Class 2: ................................................................1 A nominal, 2 A maximum
Burden:................................................................0.005 VA per phase maximum at 11 A
Pickup current:.................................................0.1% of nominal
Connections:.....................................................O or U lug (see CT Leads Terminated to Meter on page 3–
6);
Pass-through wire, 0.177" / 4.5 mm maximum diameter
(see Pass-Through Wire Electrical Connection on page
3–7);
Quick connect, 0.25" male tab
(see Quick Connect Electrical Connection on page 3–7)
Fault Withstand:..............................................100 A / 10 seconds, 300 A / 3 seconds, 500 A / 1 second
Reading:..............................................................Programmable full-scale to any CT ratio
MEASUREMENT METHODS
Voltage and current:.....................................true RMS
Power:..................................................................sampling at 400+ samples/cycle on all channels
measured; readings simultaneously
A/D conversion:...............................................6 simultaneous 24-bit analog-to-digital converters
UPDATE RATE
Watts, vars, and VA: ......................................100 ms (10 times per second)
All other parameters:....................................1 second
1–6 EPM 6000 MULTI-FUNCTION POWER METERING SYSTEM – USER GUIDE
CHAPTER 1: OVERVIEW
ACCURACY
Measured Parameters Display Range Accuracy
Voltage L-N 0 to 9999 kV or scalable 0.1% of reading
Voltage L-L 0 to 9999 V or kV scalable 0.1% of reading
Current 0 to 9999 A or kA 0.1% of reading
+/– Watts 0 to 9999 W, kW, or MW 0.2% of reading
+/– Wh 5 to 8 digits (programmable) 0.2% of reading
+/– vars 0 to 9999 vars, kvars, Mvars 0.2% of reading
+/– varh 5 to 8 digits (programmable) 0.2% of reading
VA 0 to 9999 VA, kVA, MVA 0.2% of reading
VAh 5 to 8 digits (programmable) 0.2% of reading
Power Factor (PF) ±0.5 to 1.0 0.2% of reading
Frequency 45 to 65 Hz 0.01 Hz
% THD 0 to 100% 2.0% F.S.
% Load Bar 10 digit resolution scalable 1 to 120% of reading
NOTE: Typical results are more accurate.
1.4.3 Environmental
TEMPERATURE AND HUMIDITY
Storage:...............................................................–40 to 85°C
Operating:..........................................................–30 to 70°C
Humidity:............................................................up to 95% RH, non-condensing
Faceplate rating: ............................................NEMA 12 (water resistant), mounting gasket included
1.4.4 Communications
COMMUNICATIONS FORMAT
Types:...................................................................RS485 port through back plate
COMMUNICATIONS PORTS
Protocol:..............................................................Modbus RTU, Modbus ASCII, DNP 3.0
Baud rate: ..........................................................9600 to 57600 bps
Port address: ....................................................001 to 247
Data format:.....................................................8 bits, no parity
1.4.5 Mechanical Parameters
DIMENSIONS
Size:.......................................................................4.25" × 4.82" × 4.85" (L × W × H)
Mounting:...........................................................mounts in 92 mm square DIN or ANSI C39.1 4-inch round
Weight:................................................................2 pounds / 0.907 kg
Shipping..............................................................ships in 6-inch / 152.4 mm cube container
IrDA port through face plate
105.4 mm × 123.2 mm × 123.2 mm (L × W × H)
cut-out
EPM 6000 MULTI-FUNCTION POWER METERING SYSTEM – USER GUIDE 1–7
1.4.6 Approvals
CHAPTER 1: OVERVIEW
TYPE TESTING
IEC 687 (0.2% accuracy)
ANSI C12.20 (0.2% accuracy)
ANSI (IEEE) C37.90.1: ....................................Surge Withstand
ANSI C62.41 (burst)
IEC 1999-4-2: ...................................................ESD
IEC 1000-4-3: ...................................................Radiated Immunity
IEC 1000-4-4: ...................................................Fast Transient
IEC 1000-4-5: ...................................................Surge Immunity
COMPLIANCE
ISO: ........................................................................manufactured to an ISO9001 registered program
UL:..........................................................................UL listed (file E250818)
CSA:.......................................................................Certified per: C22.2 No.1010.1 Electrical and Electronic
Measuring and Testing Equipment
CE:..........................................................................conforms to EN 55011 / EN 50082
1–8 EPM 6000 MULTI-FUNCTION POWER METERING SYSTEM – USER GUIDE
GE Consumer & Industrial
Multilin
EPM 6000 Multi-function Power
Metering System
Chapter 2: Electrical Background
Electrical Background
2.1 Three-Phase Power Measurement
2.1.1 Description
This introduction to three-phase power and power measurement is intended to provide
only a brief overview of the subject. The professional meter engineer or meter technician
should refer to more advanced documents such as the EEI Handbook for Electricity
Metering and the application standards for more in-depth and technical coverage of the
subject.
EPM 6000 MULTI-FUNCTION POWER METERING SYSTEM – USER GUIDE 2–1
2.2 Three-Phase System Configurations
2.2.1 Description
Three-phase power is most commonly used in situations where large amounts of power
will be used because it is a more effective way to transmit the power and because it
provides a smoother delivery of power to the end load. There are two commonly used
connections for three-phase power, a wye connection or a delta connection. Each
connection has several different manifestations in actual use. When attempting to
determine the type of connection in use, it is a good practice to follow the circuit back to
the transformer that is serving the circuit. It is often not possible to conclusively determine
the correct circuit connection simply by counting the wires in the service or checking
voltages. Checking the transformer connection will provide conclusive evidence of the
circuit connection and the relationships between the phase voltages and ground.
2.2.2 Wye Connection
The wye connection is so called because when you look at the phase relationships and the
winding relationships between the phases it looks like a wye (Y). The following figure
depicts the winding relationships for a wye-connected service. In a wye service the neutral
(or center point of the wye) is typically grounded. This leads to common voltages of 208/
120 and 480/277 (where the first number represents the phase-to-phase voltage and the
second number represents the phase-to-ground voltage).
CHAPTER 2: ELECTRICAL BACKGROUND
Ia
A
Van
B
C
FIGURE 2–1: Three-Phase Wye Winding
Vbn
N
Vcn
The three voltages are electrically separated by 120°. Under balanced load conditions with
unity power factor, the currents are also separated by 120°. However, unbalanced loads
and other conditions can cause the currents to depart from the ideal 120° separation.
Three-phase voltages and currents are usually represented with a phasor diagram. A
phasor diagram for the typical connected voltages and currents is shown below.
2–2 EPM 6000 MULTI-FUNCTION POWER METERING SYSTEM – USER GUIDE
CHAPTER 2: ELECTRICAL BACKGROUND
The phasor diagram shows the 120° angular separation between the phase voltages. The
phase-to-phase voltage in a balanced three-phase wye system is 1.732 times the phaseto-neutral voltage. The center point of the wye is tied together and is typically grounded.
The following table indicates the common voltages used in the United States for wyeconnected systems.
Vcn
Ic
Van
Ia
Ib
Vbn
FIGURE 2–2: Three-Phase Voltage and Current Phasors for Wye Winding
Table 2–1: Common Phase Voltages on Wye Services
Phase-to-Ground Voltage Phase-to-Phase Voltage
120 volts 208 volts
277 volts 480 volts
2400 volts 4160 volts
7200 volts 12470 volts
7620 volts 13200 volts
Usually, a wye-connected service will have four wires: three wires for the phases and one
for the neutral. The three-phase wires connect to the three phases. The neutral wire is
typically tied to the ground or center point of the wye (refer to the Three-Phase Wye
Winding diagram above).
In many industrial applications the facility will be fed with a four-wire wye service but only
three wires will be run to individual loads. The load is then often referred to as a deltaconnected load but the service to the facility is still a wye service; it contains four wires if
you trace the circuit back to its source (usually a transformer). In this type of connection
the phase to ground voltage will be the phase-to-ground voltage indicated in the table
above, even though a neutral or ground wire is not physically present at the load. The
transformer is the best place to determine the circuit connection type because this is a
location where the voltage reference to ground can be conclusively identified.
EPM 6000 MULTI-FUNCTION POWER METERING SYSTEM – USER GUIDE 2–3
2.2.3 Delta Connection
Delta connected services may be fed with either three wires or four wires. In a three-phase
delta service the load windings are connected from phase-to-phase rather than from
phase-to-ground. The following figure shows the physical load connections for a delta
service.
CHAPTER 2: ELECTRICAL BACKGROUND
A
Ia
Iab
Vab
Vca
B
Vbc
Ib
Ica
Ibc
Ic
C
FIGURE 2–3: Three-Phase Delta Winding Relationship
In this example of a delta service, three wires will transmit the power to the load. In a true
delta service, the phase-to-ground voltage will usually not be balanced because the
ground is not at the center of the delta.
The following diagram shows the phasor relationships between voltage and current on a
three-phase delta circuit.
In many delta services, one corner of the delta is grounded. This means the phase to
ground voltage will be zero for one phase and will be full phase-to-phase voltage for the
other two phases. This is done for protective purposes.
Vca
Ic
Vbc
Ia
Ib
Vab
FIGURE 2–4: Three-Phase Voltage and Current Phasors for Delta Winding
2–4 EPM 6000 MULTI-FUNCTION POWER METERING SYSTEM – USER GUIDE
CHAPTER 2: ELECTRICAL BACKGROUND
Another common delta connection is the four-wire, grounded delta used for lighting loads.
In this connection the center point of one winding is grounded. On a 120/240 volt, fourwire, grounded delta service the phase-to-ground voltage would be 120 volts on two
phases and 208 volts on the third phase. The phasor diagram for the voltages in a threephase, four-wire delta system is shown below.
120 V
Vbc
120 V
FIGURE 2–5: Three-Phase, Four-Wire Delta Phasors
Vnc
Vbn
2.2.4 Blondell's Theorem and Three-Phase Measurement
In 1893 an engineer and mathematician named Andre E. Blondell set forth the first
scientific basis for poly phase metering. His theorem states:
If energy is supplied to any system of conductors through N wires, the total power in the
system is given by the algebraic sum of the readings of N watt-meters so arranged that
each of the N wires contains one current coil, the corresponding potential coil being
connected between that wire and some common point. If this common point is on one
of the N wires, the measurement may be made by the use of N-1 wattmeters.
Vca
Vab
The theorem may be stated more simply, in modern language:
In a system of N conductors, N – 1 meter elements will measure the power or energy
taken provided that all the potential coils have a common tie to the conductor in which
there is no current coil.
Three-phase power measurement is accomplished by measuring the three individual
phases and adding them together to obtain the total three phase value. In older analog
meters, this measurement was made using up to three separate elements. Each element
combined the single-phase voltage and current to produce a torque on the meter disk. All
three elements were arranged around the disk so that the disk was subjected to the
combined torque of the three elements. As a result the disk would turn at a higher speed
and register power supplied by each of the three wires.
According to Blondell's Theorem, it was possible to reduce the number of elements under
certain conditions. For example, a three-phase, three-wire delta system could be correctly
measured with two elements (two potential coils and two current coils) if the potential coils
were connected between the three phases with one phase in common.
EPM 6000 MULTI-FUNCTION POWER METERING SYSTEM – USER GUIDE 2–5
CHAPTER 2: ELECTRICAL BACKGROUND
In a three-phase, four-wire wye system it is necessary to use three elements. Three voltage
coils are connected between the three phases and the common neutral conductor. A
current coil is required in each of the three phases.
In modern digital meters, Blondell's Theorem is still applied to obtain proper metering. The
difference in modern meters is that the digital meter measures each phase voltage and
current and calculates the single-phase power for each phase. The meter then sums the
three phase powers to a single three-phase reading.
Some digital meters calculate the individual phase power values one phase at a time. This
means the meter samples the voltage and current on one phase and calculates a power
value. Then it samples the second phase and calculates the power for the second phase.
Finally, it samples the third phase and calculates that phase power. After sampling all three
phases, the meter combines the three readings to create the equivalent three-phase
power value. Using mathematical averaging techniques, this method can derive a quite
accurate measurement of three-phase power.
More advanced meters actually sample all three phases of voltage and current
simultaneously and calculate the individual phase and three-phase power values. The
advantage of simultaneous sampling is the reduction of error introduced due to the
difference in time when the samples were taken.
Blondell's Theorem is a derivation that results from Kirchhoff's Law. Kirchhoff's Law states
that the sum of the currents into a node is zero. Another way of stating the same thing is
that the current into a node (connection point) must equal the current out of the node. The
law can be applied to measuring three-phase loads. The figure below shows a typical
connection of a three-phase load applied to a three-phase, four-wire service. Kirchhoff's
Laws hold that the sum of currents A, B, C and N must equal zero or that the sum of
currents into Node “n” must equal zero.
C
B
Phase B
Phase C
Node "n"
Phase A
A
N
FIGURE 2–6: Three-Phase Load Illustrating Kirchhoff’s Law and Blondell’s Theorem
2–6 EPM 6000 MULTI-FUNCTION POWER METERING SYSTEM – USER GUIDE
CHAPTER 2: ELECTRICAL BACKGROUND
If we measure the currents in wires A, B and C, we then know the current in wire N by
Kirchhoff's Law and it is not necessary to measure it. This fact leads us to the conclusion of
Blondell's Theorem that we only need to measure the power in three of the four wires if
they are connected by a common node. In the circuit of Figure 1.6 we must measure the
power flow in three wires. This will require three voltage coils and three current coils (a
three element meter). Similar figures and conclusions could be reached for other circuit
configurations involving delta-connected loads.
EPM 6000 MULTI-FUNCTION POWER METERING SYSTEM – USER GUIDE 2–7
2.3 Power, Energy, and Demand
2.3.1 Description
It is quite common to exchange power, energy, and demand without differentiating
between the three. Because this practice can lead to confusion, the differences between
these three measurements will be discussed.
2.3.2 Power
Power is an instantaneous reading. The power reading provided by a meter is the present
flow of watts. Power is measured immediately just like current. In many digital meters, the
power value is actually measured and calculated over a one-second interval, since it takes
some amount of time to calculate the RMS values of voltage and current. However, this
time interval is kept small to preserve the instantaneous nature of power.
2.3.3 Energy
CHAPTER 2: ELECTRICAL BACKGROUND
Energy is always based upon some time increment – it is the integration of power over a
defined time increment. Energy is an important value because almost all electric bills are
based, in part, on the amount of energy consumed.
Typically, electrical energy is measured in units of kilowatt-hours (kWh). A kilowatt-hour
represents a constant load of 1000 watts (1 kW) for 1 hour. Stated another way, if the
power delivered (instantaneous watts) is measured as 1000 W, and the load was served for
a one-hour time interval, then the load would have absorbed 1 kWh of energy. A different
load may have a constant power requirement of 4000 W. If this load were served for one
hour, it would absorb 4 kWh of energy. Likewise, if it were served for 15 minutes, it would
absorb ¼ of that total, or 1 kWh.
The following figure shows a graph of power and the resulting energy that would be
transmitted as a result of the illustrated power values. For this illustration, it is assumed
that the power level is held constant for each minute when a measurement is taken. Each
bar in the graph represents the power load for the one-minute increment of time. In real
life, the power values are continually moving.
2–8 EPM 6000 MULTI-FUNCTION POWER METERING SYSTEM – USER GUIDE
CHAPTER 2: ELECTRICAL BACKGROUND
kilowatts
80
70
60
50
40
30
20
10
0
123456789101112131415
Time (minutes)
FIGURE 2–7: Power Use Over Time
The data in the above figure is reproduced in the following table to illustrate the
calculation of energy. Since the time increment of the measurement is one minute, and
since we specified a constant load over that minute, the power reading can be converted
to an equivalent consumed energy reading by multiplying the power reading by 1/60
(converting the time base from minutes to hours).
EPM 6000 MULTI-FUNCTION POWER METERING SYSTEM – USER GUIDE 2–9
CHAPTER 2: ELECTRICAL BACKGROUND
Table 2–2: Power and Energy Relationship Over Time
Time Interval Power Energy Accumulated
Energy
1 minute 30 kW 0.50 kWh 0.50 kWh
2 minutes 50 kW 0.83 kWh 1.33 kWh
3 minutes 40 kW 0.67 kWh 2.00 kWh
4 minutes 55 kW 0.92 kWh 2.92 kWh
5 minutes 60 kW 1.00 kWh 3.92 kWh
6 minutes 60 kW 1.00 kWh 4.92 kWh
7 minutes 70 kW 1.17 kWh 6.09 kWh
8 minutes 70 kW 1.17 kWh 7.26 kWh
9 minutes 60 kW 1.00 kWh 8.26 kWh
10 minutes 70 kW 1.17 kWh 9.43 kWh
11 minutes 80 kW 1.33 kWh 10.76 kWh
12 minutes 50 kW 0.83 kWh 12.42 kWh
13 minutes 50 kW 0.83 kWh 12.42 kWh
14 minutes 70 kW 1.17 kWh 13.59 kWh
2.3.4 Demand
15 minutes 80 kW 1.33 kWh 14.92 kWh
As shown in the above table, the accumulated energy for the power load profile of the
data in Power Use Over Time on page 2–9 is 14.92 kWh.
Demand is also a time-based value. The demand is the average rate of energy use over
time. The actual label for demand is kilowatt-hours/hour but this is normally reduced to
kilowatts. This makes it easy to confuse demand with power. But demand is not an
instantaneous value. To calculate demand it is necessary to accumulate the energy
readings (as illustrated in Power Use Over Time on page 2–9) and adjust the energy reading
to an hourly value that constitutes the demand.
In the example, the accumulated energy is 14.92 kWh. But this measurement was made
over a 15-minute interval. To convert the reading to a demand value, it must be
normalized to a 60-minute interval. If the pattern were repeated for an additional three 15minute intervals the total energy would be four times the measured value or 59.68 kWh.
The same process is applied to calculate the 15-minute demand value. The demand value
associated with the example load is 59.68 kWh/hour or 59.68 kWd. Note that the peak
instantaneous value of power is 80 kW, significantly more than the demand value.
2–10 EPM 6000 MULTI-FUNCTION POWER METERING SYSTEM – USER GUIDE
CHAPTER 2: ELECTRICAL BACKGROUND
The following figure illustrates another example of energy and demand. In this case, each
bar represents the energy consumed in a 15-minute interval. The energy use in each
interval typically falls between 50 and 70 kWh. However, during two intervals the energy
rises sharply and peaks at 100 kWh in interval #7. This peak of usage will result in setting a
high demand reading. For each interval shown the demand value would be four times the
indicated energy reading. So interval 1 would have an associated demand of 240 kWh/hr.
Interval #7 will have a demand value of 400 kWh/hr. In the data shown, this is the peak
demand value and would be the number that would set the demand charge on the utility
bill.
100
80
60
40
kilowatt-hours
20
0
12345678
FIGURE 2–8: Energy Use and Demand Intervals
Intervals (15 mins.)
As seen in this example, it is important to recognize the relationships between power,
energy and demand in order to effectively control loads or to correctly monitor use.
EPM 6000 MULTI-FUNCTION POWER METERING SYSTEM – USER GUIDE 2–11
2.4 Reactive Energy and Power Factor
2.4.1 Real, Reactive, and Apparent Power
The real power and energy measurements discussed in the previous section relate to the
quantities that are most used in electrical systems. But it is often not sufficient to only
measure real power and energy. Reactive power is a critical component of the total power
picture because almost all real-life applications have an impact on reactive power.
Reactive power and power factor concepts relate to both load and generation
applications. However, this discussion will be limited to analysis of reactive power and
power factor as they relate to loads. To simplify the discussion, generation will not be
considered.
Real power (and energy) is the component of power that is the combination of the voltage
and the value of corresponding current that is directly in phase with the voltage. However,
in actual practice the total current is almost never in phase with the voltage. Since the
current is not in phase with the voltage, it is necessary to consider both the in-phase
component and the component that is at quadrature (angularly rotated 90° or
perpendicular) to the voltage. The following figure shows a single-phase voltage and
current and breaks the current into its in-phase and quadrature components.
CHAPTER 2: ELECTRICAL BACKGROUND
I
V
R
θ
I
X
FIGURE 2–9: Voltage and Complex Current
I
The voltage (V) and the total current (I) can be combined to calculate the apparent power
or VA. The voltage and the in-phase current (I
watts. The voltage and the quadrature current (I
) are combined to produce the real power or
R
) are combined to calculate the reactive
X
power.
The quadrature current may be lagging the voltage (as shown above) or it may lead the
voltage. When the quadrature current lags the voltage the load is requiring both real
power (watts) and reactive power (vars). When the quadrature current leads the voltage
the load is requiring real power (watts) but is delivering reactive power (vars) back into the
system; that is VARs are flowing in the opposite direction of the real power flow.
Reactive power (vars) is required in all power systems. Any equipment that uses
magnetization to operate requires vars. Usually the magnitude of vars is relatively low
compared to the real power quantities. Utilities have an interest in maintaining VAR
requirements at the customer to a low value in order to maximize the return on plant
invested to deliver energy. When lines are carrying vars, they cannot carry as many watts.
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So keeping the var content low allows a line to carry its full capacity of watts. In order to
encourage customers to keep VAR requirements low, most utilities impose a penalty if the
var content of the load rises above a specified value.
2.4.2 Power Factor
A common method of measuring reactive power requirements is power factor. Power
factor can be defined in two different ways. The more common method of calculating
power factor is the ratio of the real power to the apparent power. This relationship is
expressed in the following formula:
Total PF
real power
----------------------------------------
apparent power
watts
------------- -==
VA
(EQ 2.1)
This formula calculates a power factor quantity known as Total Power Factor. It is called
Total PF because it is based on the ratios of the power delivered. The delivered power
quantities will include the impacts of any existing harmonic content. If the voltage or
current includes high levels of harmonic distortion the power values will be affected. By
calculating power factor from the power values, the power factor will include the impact of
harmonic distortion. In many cases this is the preferred method of calculation because the
entire impact of the actual voltage and current are included.
A second type of power factor is Displacement Power Factor. Displacement PF is based on
the angular relationship between the voltage and current. Displacement power factor
does not consider the magnitudes of voltage, current or power. It is solely based on the
phase angle differences. As a result, it does not include the impact of harmonic distortion.
Displacement power factor is calculated using the following equation:
Displacement PF θcos=
(EQ 2.2)
where θ is the angle between the voltage and the current (see FIGURE 2–9: Voltage and
Complex Current on page 2–12).
In applications where the voltage and current are not distorted, the Total Power Factor will
equal the Displacement Power Factor. But if harmonic distortion is present, the two power
factors will not be equal.
EPM 6000 MULTI-FUNCTION POWER METERING SYSTEM – USER GUIDE 2–13
2.5 Harmonic Distortion
2.5.1 Harmonics of a Non-Sinusoidal Waveform
Harmonic distortion is primarily the result of high concentrations of non-linear loads.
Devices such as computer power supplies, variable speed drives and fluorescent light
ballasts make current demands that do not match the sinusoidal waveform of AC
electricity. As a result, the current waveform feeding these loads is periodic but not
sinusoidal. The following figure shows a normal, sinusoidal current waveform with a period
of a. This example has no distortion.
CHAPTER 2: ELECTRICAL BACKGROUND
1000
500
0
Current (amps)
–500
–1000
a
FIGURE 2–10: Non-Distorted Current Waveform
t
2a
The figure below shows a current waveform with a slight amount of harmonic distortion.
The waveform is still periodic and is fluctuating at the normal 60 Hz frequency (a = 1/60
second). However, the waveform is not the smooth sinusoidal form seen above.
1500
1000
500
0
Current (amps)
–500
a
t
2a
–1000
–1500
FIGURE 2–11: Distorted Current Waveform
The distortion above can be modeled as the sum of several sinusoidal waveforms of
frequencies that are multiples of the fundamental 60 Hz frequency. This modeling is
performed by mathematically reducing the distorted waveform into a collection of higher
2–14 EPM 6000 MULTI-FUNCTION POWER METERING SYSTEM – USER GUIDE
CHAPTER 2: ELECTRICAL BACKGROUND
frequency waveforms. These higher frequency waveforms are referred to as harmonics.
The following figure shows the content of the harmonic frequencies that comprise one
cycle of the distorted portion of the above waveform.
250
200
150
100
50
0
-50
Current (amps)
-100
-150
-200
-250
t
a
FIGURE 2–12: Harmonics for Distorted Current Waveform
The waveforms above provide an indication of the impact of combining multiple harmonic
frequencies together. The broken lines represent the 3rd, 5th, and 7th current harmonics.
The solid line represents the sum of the three harmonics.
When harmonics are present, it is important to remember that they are operating at
higher frequencies. As such, they do not always respond in the same manner as 60 Hz
values.
2.5.2 Inductive and Capacitive Impedance
Inductive and capacitive impedance are present in all power systems. We are accustomed
to thinking about these impedances as they perform at 60 Hz. However, these impedances
are subject to frequency variation.
XLjω L and XC1 jωC⁄==
At 60 Hz, ω = 377; but at 300 Hz (5th harmonic) ω = 1885. As frequency changes, the
impedance changes and system impedance characteristics that are normal at 60 Hz may
be entirely different in the presence of higher order harmonic waves.
Traditionally, the most common harmonics have been the low order odd frequencies, such
as the 3rd, 5th, 7th, and 9th. However newer, new-linear loads are introducing significant
quantities of higher order harmonics.
(EQ 2.3)
2.5.3 Voltage and Current Monitoring
Since much voltage monitoring and almost all current monitoring is performed using
instrument transformers, the higher order harmonics are often not visible. Instrument
transformers are designed to pass 60 Hz quantities with high accuracy. These devices,
when designed for accuracy at low frequency, do not pass high frequencies with high
EPM 6000 MULTI-FUNCTION POWER METERING SYSTEM – USER GUIDE 2–15
accuracy; at frequencies above about 1200 Hz they pass almost no information. So when
instrument transformers are used, they effectively filter out higher frequency harmonic
distortion making it impossible to see.
However, when monitors can be connected directly to the measured circuit (such as direct
connection to 480 V bus) the user may often see higher order harmonic distortion. An
important rule in any harmonics study is to evaluate the type of equipment and
connections before drawing a conclusion. Not being able to see harmonic distortion is not
the same as not having harmonic distortion.
2.5.4 Waveform Capture
It is common in advanced meters to perform a function commonly referred to as
waveform capture. Waveform capture is the ability of a meter to capture a present picture
of the voltage or current waveform for viewing and harmonic analysis. Typically a
waveform capture will be one or two cycles in duration and can be viewed as the actual
waveform, as a spectral view of the harmonic content, or a tabular view showing the
magnitude and phase shift of each harmonic value. Data collected with waveform capture
is typically not saved to memory. Waveform capture is a real-time data collection event.
Waveform capture should not be confused with waveform recording that is used to record
multiple cycles of all voltage and current waveforms in response to a transient condition.
CHAPTER 2: ELECTRICAL BACKGROUND
2–16 EPM 6000 MULTI-FUNCTION POWER METERING SYSTEM – USER GUIDE
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