Megger MIT510/2 Manuel utilisateur

MIT510/2

5kV Digital Insulation Tester

USER MANUAL

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.

GSAFETY WARNINGS

Safety Warning must be observed during use.

nThe 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.

nCircuit connections must not be touched during an insulation test.

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

nTested 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.

nThe voltage indicator and automatic discharge features should be regarded as additional safety features and not a substitute for normal safe working

practice.

nIt 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.

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

nThe instrument should not be used if any partof it is damaged.

nInsulation testing in wet weather conditions might be hazardous. It is recommended that this instrument is not used in these circumstances. If this is

unavoidable, the user must takeall necessary precautions.

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

Symbols used on the instrument are:

FCaution: risk of electric shock

GCaution: refer to accompanying notes

tEquipment protected throughout by Double

Insulation (Class II)

cEquipment 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.

Cleaning

Disconnect the instrument and wipe it with a clean cloth slightly damped

with soapy water or Isopropyl alcohol (IPA).

CONTENTS

Safety warnings 2

Cleaning 3

Introduction 4

Power lead and charging 4

Instrument controls and indicators 5

Power On/Off button 6

Test voltage sand tbuttons 6

Test start/stop button 6

Ω/I button 6

Bbutton 6

High voltage warning LED 6

Line input present LED 7

Test terminals 7

Guard terminal 7

Factory programming socket 7

Battery bar graph 8

Voltage at terminals 8

Timer indicator 8

Digital display 8

Analogue display 8

Capacitance display 9

Time constant 9

Measurements above 100 GΩ9

Circuit block diagram 10

Specification 10

Accessories 12

Repair and Warranty 13

If the power lead supplied is not suitable for your type of mains outlet, do

not use an adaptor. Always use a power lead fitted with the correct plug.

NB: A plug severed from the power lead is a hazard if plugged into a live

socket. Severed plugs must be destroyed immediately.

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 cable colour coding:

International USA

Earth/Ground Yellow/Green Green

Neutral Blue White

Live (Line) Brown Black

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

The instrument can be powered from 95 - 240 V rms, ±10% 50/60Hz.

With power connected the battery will charge as long as a test is not in

progress. The Power On/Off button has a green LED which illuminates

when mains power is present.

For best battery lifetime, charge the battery after each use. A completely

exhausted battery will take 14 hours to recharge.

INTRODUCTION POWER LEAD AND CHARGING

The MIT510/2 is a compact microprocessor controlled high voltage d.c.

insulation tester, powered by internal rechargeable battery or mains

supply. A comprehensive LCD display shows resistance, current,

capacitance, voltage and timer measurements digitally, with resistance

being shown in analogue as well.

Features include:

nResistance or current measurement- front panel selectable

nResistance measurement range - 10 kΩto 15 TΩ

nFront panel selectable test voltages - 250 V, 500 V, 1000 V, 2500 V, 5000 V

nIncremental timer (minutes & seconds) – measures during test

nLoad capacitance measurement – displayed at end of a test

nLCD backlight – front panel selectable

nBattery level/charging indicator

nMains (line) input presence LED

nHigh voltage warning flashing LED shows when greater than 50 V

present on test leads

nHigh voltage warning LCD "flash" shows when greater than 50 V

present on test leads

n8hours continuous testing on full charge.

8. Tostop the test press TEST button.

9. Timer will stop.

10. Analogue display shows insulation resistance.

11. Digital display shows resistance or current selected by pressing Ω/I

button.

12. Load capacitance will be calculated and displayed after the end of

the test.

13. Time-constant will be displayed after the end of the test.

INSTRUMENT CONTROLS AND INDICATORS

1. Check connections to load - see SAFETY WARNINGS

2. To turn on, press Power On/Off button and release after display

responds. The instrument first will perform a self-check during which

Ini is displayed. After Ini disappears the instrument is ready for use.

3. Check voltage at terminals display to be sure the load is safe to

energise.

4. Set test voltage required with Vsand Vtbuttons.

5. To start a test, press TEST button and release after red LED shows. If

external voltage at terminals <50 V, testing starts.

6. TEST button red LED and display warning symbols will flash during a

test to show high voltage present at terminals.

7. Timer will count up from zero during test.

Voltage at terminals

Battery level

Warning

voltage at

terminals

Digital

display

Timer

Analogue

display

Warning

voltage at

terminals

Capacitance display

Time constant

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 sand tbuttons

Using these buttons one of five test voltages can be selected: 250 V, 500 V,

1kV, 2.5 kV, and 5 kV. The selected voltage is shown on the display.

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 sor tbutton will

then display the test voltage immediately before the end of the test.

Test start / stop button

Atest 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.

Atest 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.

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 display between the insulation

resistance and current.

Bbutton

Pressing this button toggles the display backlight on and off.

High voltage warning LED

This is a red LED next to the TEST button on the front panel. The LED

flashes when the voltage on the test inputs exceeds 50 V.

The guard terminal is at the same potential as the negative terminal. Since

the leakage resistance is effectively in parallel with the resistance to be

measured, the use of the guard causes the current flowing through surface

leakage to be diverted from the measuring circuit. The instrument

therefore reads the leakage of the insulator, ignoring leakage across its

surface. The display will show ‘FUS’ if the internal guard terminal fuse is

found to have blown. The instrument must be switched off to clear the

message before further testing is permitted. The fuse should be replaced

by an authorised repairer.The instrument may be used in the mean time if

the guard terminal not used. Refer to notes regarding measurements

above 100 GΩon page 9.

Factory programming socket

This is a 9 pin socket under the hinged cover and is not for customer use.

Line input present LED

This is a green LED next to the power On/Off button on the front panel. It

is illuminated whenever the mains power is connected.

Test terminals

There are three test terminals marked +, - and G. These terminals are

designed to accept only the test leads supplied. Shutters across the

terminals prevent accidental ingress of dirt and other objects. Test lead

plugs interlock with the shutters and are released by rotating the test lead

plug a quarter turn.

The Guard terminal is explained below and is only used in cases where

surface leakage currents need to be eliminated. Most measurements use

just the + and – terminals. The instrument’s internal voltage generator

drives the + terminal with respect to the – terminal, current being

measured in the – terminal.

Guard terminal

For basic insulation tests and where there is little possibility of surface

leakage affecting the measurement, it is unnecessaryto use the guard

terminal i.e. if the insulator is clean and there are unlikely to be any adverse

current paths. However in cable testing for example, there may be surface

leakage paths across the insulation between the bare cable and the external

sheathing due to the presence of moisture or dirt. Where it is required to

remove the effect of this leakage, particularly at high testing voltages, a

bare wire may be bound tightly around the insulation and connected via

the third test lead to the guard terminal ‘G’.

instrument will not perform a test. The high voltage warning indicators

flash, and the beeper sounds, to warn of the hazard until the external

voltage becomes less than 50 V.

When testing, the voltage displayed is the voltage present at the test

terminals of the instrument. If the test voltage is changed, by pressing

either of the test voltage sand tbuttons during a test, the new test

voltage is displayed momentarily.

After testing, the voltage displayed is the voltage present on the terminals.

To see what the voltage was immediately prior to the end on the test,

press either test voltage sor tbuttons.

Timer indicator

The timer shows minutes and seconds. At the start of a test the timer will

start from zero and at the end of a test it will stop. The duration of the last

test remains on the display until another test is started.

Digital Display

The digital display shows the resistance or current being measured during

a test. The Ω/I button toggles between the two. After a test the display

shows the last measurement made until the timer or voltage test settings

are changed or the test start/stop button is pressed.

Analogue display

This simulates an analogue meter movement to give the user a better

"feel" for how a measurement is progressing. The analogue display shows

resistance only.

Battery bar graph

This is a battery symbol on the LCD display comprising 4 pairs of

segments. The battery is monitored continuously when the instrument is

turned on. The charge remaining in the battery is shown in the table

below.

Fully charged battery

50% charged battery

Tests cannot be started, and the batterymay fail

at any time.

Symbol flashes when there is not enough charge

for a test. The instrument then turns itself off

When mains power is present the indicator shows the battery is being

charged by animating the segments of the bar graph.

Voltage at terminals

The test voltage will default to that selected in the previous test. If the

instrument has been switched off since the previous test, the test voltage

defaults to 250 V.

If there is an external voltage greater than 50 V present, this will be

displayed regardless of changes made to the test voltage. In this case the

Capacitance display

At the end of a test the capacitance of the circuit under test is calculated

and displayed. After a test the display shows the last measurement made

until the Vs, Vt,or TEST buttons are pressed.

Time constant:

At the end of a test the time constant of the circuit under test is calculated

and displayed. After a test the display shows the last measurement made

until the Vs, Vt,or TEST buttons are pressed.

Measurements above 100 GΩ

Measurements up to 100 GΩcan be made without any special precautions,

assuming that the test leads are reasonably clean and dry. The guard lead

can be used to remove the effects of surface leakage if necessary. When

measuring resistances above 100 GΩ, the test leads should not be allowed

to touch each other, or any other object since this will introduce leakage

paths. Sharp points at the test lead connections should also be avoided

since this will encourage corona discharge.

The output is isolated, and so will float relative to ground such that the

positive terminal is at plus half of the test voltage, and the negative terminal

is at minus half of the test voltage with respect to ground. Leakages

therefore occur between the positive terminal and ground, between the

negative terminal and ground, and directly between the positive and

negative terminals. These leakages have a significant effect and can occur

through the air itself.

If the guard lead is connected to ground, then since the negative terminal

is at the same voltage as the guard terminal, the leakage into the negative

terminal will be considerably reduced. This will improve accuracy because

the current flowing into the negative terminal is measured by the

instrument and used to calculate resistance. This technique is only

permissible if the item under test is isolated from ground. “Isolated” in

this context means insulated by a resistance of at least 5 MΩfor the

positive terminal, or at least 10 kΩfor the negative terminal.

Conversely, if the positive terminal is grounded, then the negative terminal

will be at a voltage equal to the test voltage relative to ground, which will

result in an increase in leakage current, and worsening of measurement

accuracy.

When making measurements above 100 GΩtherefore, the user should

ground the Guard Lead where possible, otherwise parallel leakage paths

may occur.

Alternatively, screened leads are available as an optional accessory from

Megger. The lead to the negative terminal is fully screened. The screen is

plugged into the Guard terminal, diverting any stray leakage currents. This

considerably improves measurements made with a floating output, where

the leads might touch each other or anything other than the test piece.

+Test V

-Test V

Ground

+Test V 0V

Ground

Guard

Voltage input range

85-265 V rms, 50/60Hz, 60 VA

Battery life

Typical capacity is 6 hours continuous testing at 5 kV with a 100 MΩload

Test voltages

250 V, 500 V, 1000 V, 2500 V, 5000 V

Accuracy (23°C, 5 kV)

±5% @ 1 TΩ

±20% @ 10 TΩ

Guard

2% error guarding 500 kΩleakage with 100 MΩload

Display range

Digital display (3 digits) 10 kΩto 15 TΩ

Analogue display 100 kΩto 1 TΩ

Short circuit/charge current

3mA @ 5 kV

Capacitor charge time

<3 seconds per µF at 3mA to 5 kV

Capacitor discharge time

<120 ms per µF to discharge from 5000 V to 50 V

Capacitance measurement (500 V minimum test voltage)

10 nF to 50 µF (dependent on test voltage)

Capacitance measurement accuracy (23°C)

±5% ±5 nF

Circuit block diagram

For 5 kV instruments C1 = 47 nF, R1 = 50 kΩ, R2 = 40 kΩ

For 10 kV instruments C1 = 15 nF, R1 = 156 kΩ, R2 = 110 kΩ

SPECIFICATION

100 MΩ

R1 R2

Volts

Fuse

Cable

under

test

Discharge

resistance

Current

Ref

Voltage

control

Current

Limit

High

voltage

source

Table des matières

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