Megger MIT520/2 Instruction Manual

M

MIT520/2

5kV Digital Insulation Tester

USER MANUAL

GSAFETY WARNINGS

Safety Warning must be observed during use.

■The circuit under test must be switched off, de-energised, isolated and checked to be safe before insulation test connections are made. Make sure the circuit is not re-energised whilst the instrument is connected.

■Circuit connections must not be touched during an insulation test.

■After completing a test, capacitive circuits must be completely discharged before disconnecting the test leads. Capacitive charges can be lethal.

■Tested items should be firmly shorted out with a shorting link, after discharge, until required for use. This is to guard against any stored dielectric absorption charge subsequently being released thereby raising the voltage to potentially dangerous levels.

■The voltage indicator and automatic discharge features should be regarded as additional safety features and not a substitute for normal safe working practice.

■It is rare, but in certain circumstances, breakdown of the circuit under test may cause the instrument to terminate the test in an uncontrolled manner, possibly causing a loss of display while the circuit remains energised. In this event, the unit must be turned off and the circuit discharged manually.

■Test leads, including crocodile clips, must be in good order, clean and with no broken or cracked insulation.

■The instrument should not be used if any part of it is damaged.

■Insulation testing in wet weather conditions might be hazardous. It is recommeded that this instrument is not used in these circumstances. If this unavoidable, the user must take all necessary precautions.

■This instrument is not intrinsically safe and must not be used in hazardous atmospheres.

NOTE

THE INSTRUMENT MUST ONLY BE USED BY SUITABLY TRAINED AND COMPETENT PERSONS.

Users of this equipment and/or their employers are reminded that National Health and Safety Legislation requires them to carry out valid risk assessments of all electrical work so as to identify potential sources of electrical danger and risk of electrical injury such as inadvertent short circuits. Where the assessments show that the risk is significant then the use of fused test leads may be appropriate.

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CONTENTS

Safety warnings	2
Introduction	4
General description	4
Features	4
Cleaning	4
Power lead and battery charging	5
Instrument controls and indicators	6
Power On/Off button	7
Test voltage ▲ and ▼ buttons	7
Test start / stop button	7
Ω/I button	7
Bbutton	10
Fn button	10
Mode button	10
Timer ▲ and ▼ buttons	11
Record button	11
Recording to on-board memory	11
Downloading results	11
Deleting results	11
Recording to a PC	12
High voltage warning LED	12
Line input present LED	12
Test terminals	12
Guard terminal	12
RS232 / USB connections	13
Battery bar graph	13
Voltage at terminals	13
Timer indicator	13
Digital display	13
Analogue display	14
Secondary display	14
Pre-Test / during test key action table	14
Test mode summary	15
Insulation resistance ‘IR’ test	15

Breakdown mode / burn mode	15
Alarm limit mode	15
Step voltage ‘SV’ test	16
Polarisation index ‘PI’ test, and dielectric absorption
ratio ‘DAR’ test	16
Dielectric discharge ‘DD’ test	16
Measurements above 100 GΩ	17
Circuit block diagram	18
Specifications	19
Accessories	20
Repair and warranty	21

Symbols used on the instrument are:

F Caution: risk of electric shock

G Caution: refer to accompanying notes

t Equipment protected throughout by Double Insulation (Class II)

c Equipment complies with current EU directives.

Terms used in this manual

The word must is used to indicate that the instructions following should be followed under all circumstances. Failure to follow these instructions could result in damage to the instrument and / or a hazard to the operator.

The word should is used to indicate that the instructions indicate best practice.

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INTRODUCTION

General Description

The MIT520/2 is a microprocessor controlled 5 kV insulation tester offering measurement capability of up to 15 TΩ. The instrument performs automatic tests and has data storage and data retrieval facilities.

Polarization index and dielectric discharge tests are performed automatically, and test duration and voltages can be adjusted according to user preference for these tests. A step voltage test can be performed automatically, with a default voltage of 1 kV, and test duration of 5 minutes. It is possible for the user to set different voltages and test durations for the step voltage test.

The MIT520/2 can be powered from the mains supply or by its own internal rechargeable battery, which provides for at least 6 hours of continuous testing with a 100 MΩ load. A battery level indicator on the LCD display indicates battery capacity. Connecting power to the mains supply connector will automatically charge the battery whether the instrument is switched ‘on’ or ‘off’, except during testing. A high level of internal isolation allows the instrument to be used while the unit is supplied from the mains. An internal battery management system switches the instrument off after ten minutes of inactivity. If the battery approaches a very low state of charge the instrument turns itself off, and mains power must be applied before the instrument can be used again. Recorded test results and settings will not be lost when the instrument is switched off.

A comprehensive LCD display shows resistance, current, capacitance, time constant, voltage, timer measurements, and figure of merit measurements such as polarisation index.

Features

■Continuous resistance or current measurement on main display.

■Optional resistance, current, or figure of merit measurements on secondary display.

■Standard test voltages – 250 V, 500 V, 1 kV, 2.5 kV, 5 kV

■Non-standard test voltages – selectable between 50 V and 1 kV in 10 V steps, and selectable between 1 kV and 5 kV in 25 V steps.

■Test modes include insulation resistance, polarisation index, step voltage and dielectric discharge.

■The dielectric absorption ratio is automatically calculated if the corresponding timers are set.

■Either burn or breakdown selectable in insulation resistance mode.

■Insulation ‘Alarm Limit’ available in insulation resistance mode.

■Programmable timers include a main test duration timer, plus T1 and T2 timers for time resistance method type tests.

■Load capacitance and time constant measurements – displayed at end of test.

■LCD backlight.

■Data storage, data retrieval and real time data output.

■USB or RS232 communications.

■Battery level / charge level indicator.

Cleaning

Disconnect the instrument and wipe it with a clean cloth slightly damped with soapy water or Isopropyl alcohol (IPA).

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POWER LEAD AND BATTERY CHARGING

If the power lead supplied is not suitable for your mains connection, do not use an adaptor. Always use a power lead fitted with the correct plug.

The instrument is fitted with a two-pin IEC60320 power inlet. Most power leads are made with three-core cable, so the ground connection will not be used.

Power lead connection table

Connection	UK/International	USA
Earth/Ground	Yellow/Green	Green
Neutral	Blue	White
Live (Line)	Brown	Black

If using a fused plug, ensure that it is fitted with a 3 Amp fuse.

The instrument can be powered from 85 - 265 Vrms a.c. at 50/60 Hz. The battery will charge as long as the mains supply is connected, except when a test is in progress. The power On/Off button has a green LED, which illuminates when mains power is present. For optimum battery life, charge the battery after each use. A completely exhausted battery will take 14 hours to recharge.

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INSTRUMENT CONTROLS AND INDICATORS

Line	USB RS232	Measurement terminals			Voltage at	Test modes	Burn indicator Alarm		Data recording
input		-ve	guard	+ve	terminals
				Time ▲ and	Battery level				Timers
				▼ selectors					Main, T1,
Voltage ▲									T2
				Line input
▼ selectors
				Present	Breakdown
									Analogue
				indicator
					indicator
									display
				Power on/off
					High voltage				High
Backlight				Ω/I selector					voltage
					warning
									warning
on/off					indicator
									indicator
				Data record
Function	Mode		Test start/stop	High voltage	Dielectric
					absorption	Digital	Polarisation	Time	Capacitance
				warning indicator
					ratio/T1 timer	display	index/timer T2	constant	display

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Power On/Off button

The instrument will only turn on if this button is pressed, held and then released when the display responds. The instrument will not turn on if the button is released before the display responds, or if the button is held down for too long. This is a safety feature to prevent the instrument being inadvertently turned on.

The instrument is turned off either by pressing the button again, or if the instrument is running on the battery, by timing out after 10 minutes of inactivity.

Upon switching the instrument on the display will first show ‘Ini’ while it undergoes a self-checking routine. When Ini disappears, the instrument is ready for use.

Test voltage ▲ and ▼ buttons

Using these buttons one of five test voltages can be selected: 250 V, 500 V, 1 kV, 2.5 kV, and 5 kV. The selected voltage is shown on the display.

A non standard voltage between 50 V and 5 kV can be selected by holding down the ‘Fn’ function button whilst operating the buttons. The selectable voltage is adjustable in 10 V steps between 50 V and 1 kV, and adjustable in 25 V steps between 1 kV and 5 kV. An auto repeat facility is enabled when the button is held down, allowing faster travel through the range.

If there is an external voltage greater than 50 V on the test leads, the high voltage warning indicators are flashed, and the display shows this voltage instead. The instrument will not perform a test if this voltage is greater than 50 V.

During a test the display shows the actual voltage on the test leads. If the test voltage is changed during a test, the new test voltage will be displayed briefly.

When the test has stopped, the display continues to show the voltage present on the test leads. Pressing either test voltage ▲ or ▼ button will then display the test voltage immediately before the end of the test.

Test start / stop button

A test will only start if this button is pressed, held and then released as soon as the red high voltage warning indicator LED lights. The LCD and red LED high voltage warning indicators flash when the test starts.

A test will not start if the button is released before the red LED shows, or pressed continuously for longer than 5 seconds. This is a safety feature to prevent a test being started inadvertently.

The presence of a voltage greater than 50 V on the test leads is indicated with flashing high voltage warning indicators. Testing is disabled if the external voltage exceeds 50 V.

Testing will stop if the test start / stop button is pressed again, the preset test time is reached, or, if the unit is not in burn mode, insulation breakdown is detected.

When a test has finished, the instrument will discharge the load, which may take some time. The operator must always check the load has been discharged before touching the test leads.

Ω/I button

Pressing this button toggles the digital and secondary displays. The details available when scrolling the secondary display will depend upon the test mode selected, whether timers T1 and T2 have been set, and the duration of the test. The digital display toggles between insulation resistance and current.

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