Megger BM25 Bedienungsanleitung

BM25

5 kV Digital Insulation Tester

USER GUIDE

GUIDE DE L’UTILISATEUR

GEBRAUCHSANLEITUNG

GUÍA DEL USUARIO

Specification 22

Accessories 25

Appendix 1 - Results displayed at the end of each test 26

Appendix 2 - RS 232 Output information display examples 28

Repair and Warranty 29

Symbols used on the instrument

GCaution: Refer to accompanying notes.

FRisk of electric shock.

tEquipment complies with relevant EU Directives

cEquipment protected throughout by Double

Insulation (Class II).

CONTENTS Guide de l’utilisateur - p30 Gebrauchsanleitung - s50 Guía del usuario - p70

Safety Warnings 3

General Description 4

Test Mode Summary 5

Features and Controls 6

Battery Charging 7

Operation

Testing Precautions 8

Performing Tests - General 9

Testing procedures 10

Insulation Resistance Testing (R) 10

Test Current measurement (I) 10

Polarization Index Testing (PI) 10

Dielectric Discharge Testing (DD) 11

Step Voltage Testing (SV) 12

Factory settings 12

Custom timed PI test 12

Custom timed DD test 12

Setting Custom Test Time values 12

Using the Guard Terminal 13

Measurements above 100 GΩ13

Fault Conditioning (BURN) 13

Condition and Warning Indicators 14

Data Download 15

Application Notes 17

Preventive Maintenance 17

Insulation Testing Concepts 18

Application of Test Techniques

Short time or Spot Test 19

Polarization Index (PI) Test 19

Dielectric Discharge (DD) Test 19

Stress considerations 21

GSAFETY WARNINGS

■Safety Warnings and Testing Precautions must be read and understood before the instrument is used.

They must be observed during use

■The circuit under test must be switched off, de-energised and isolated before test connections are made.

■The BM25 can generate up to 2 mA at 5000 V. Circuit connections must not be touched when HV is selected.

■Circuits must be discharged before disconnecting the test leads.

■In certain circumstances, break-down of the circuit under test could cause the instrument to terminate the test, possibly causing a loss of

display while the circuit remains energised. In this event, it is important that the circuit is allowed to discharge and the instrument is turned

off before touching any connections.

■The test terminal area and charging panel recess should be kept in a dry, clean condition.

■Replacement fuses must be of the correct type and rating.

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

■Refer to Testing Precautions on page 8 for further explanations and precautions.

NOTE

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

Charging connections, mains power indicator and instrument protection

fuses are located in a splashproof protected recess in the front panel.

Specially designed lid hinges enable the lid to be removed and replaced as

required, and will protect the lid from strain or damage by unclipping itself

if unintentionally opened past its full extent.

Design safety features include:-

■The flashing HV warning LED on the front of the instrument , and the

flashing H.V. symbols on the display remind the user that hazardous

voltage is present when testing.

■External voltage >50 V displayed with flashing H.V. symbols on the

display.

■Load automatically discharged at the end of a test, and

decaying voltage (> 50 V) displayed.

■Interlocked sliding cover to prevent simultaneous access of

charging and test terminals.

■Test terminal sockets lock test leads into the case and prevent

accidental disconnection.

GENERAL DESCRIPTION

The BM25 is a compact, automated high voltage, battery powered

instrument used to carry out Polarization Index, Step Voltage, and

Dielectric Discharge tests as well as spot Insulation tests. The BM25 has a

resistance measurement capability up to 5 TΩand leakage current

measurement enables resistances up to 500 TΩto be measured.

The design of the instrument takes full advantage of microprocessor

technology and features a large, clear liquid crystal display, combining

digital and analogue readings of insulation resistance.

Set nominal voltage options of 500 V, 1000 V, 2500 V and 5000 V are

selectable. A variable output voltage setting provides a range of 25 V to

5000 V incremental in 25 V steps.

At switch on, the instrument carries out a calibration self check which

automatically adjusts the measurement system. The calibration sequence

inhibits any testing if the measurement system fails to meet preset limits.

On starting a test, the HV warning LED on the front of the instrument

flashes, together with the display HV warning symbols. The integral timer

starts automatically and displays minutes and seconds elapsed since the

start of the test. The timer can be used to set the duration of a test, and

will automatically stop the output voltage when the set time has expired.

During a test, measurements are automatically sent every 5 seconds via an

isolated optical link to the RS 232 connector to enable downloading of the

results to a computer.

Battery capacity is continuously displayed by a segmented indicator. The

indicator flashes when the battery requires recharging. Power is obtained

from two parallel connected sealed rechargeable lead acid batteries. If

either battery fails (or an internal protection fuse ruptures) the instrument

will continue to operate on the alternative battery. The battery is

recharged by external 95 - 265V a.c., 50-60 Hz, or 12 V d.c. supply.

Step Voltage Testing (SV)

This 5 minute test depends on the principle that an ideal insulator will

produce identical resistance readings at all voltages. Conversely, an

insulator which is being over stressed will show lower values at higher

voltages. Operating at either 2,5 kV or 5 kV, the voltage steps up one fifth

every minute, and successive measurements are taken. On completion,

each of the 5 separate results are sequentially displayed followed by the

capacitance value.

Fault Conditioning (Burn)

This low current feature is used to carry out continuous testing under

breakdown conditions.

General Notes:

1) A capacitance value reading is only available if the test has run for

more than one minute, and the reading was not over-range.

2) Internal discharge resistors are automatically selected :-

- At the end of a test.

- If the instrument is switched off.

- If an internal error is detected.

Any voltage remaining on the terminals at the end of a test,will be

displayed until it has decayed to less than 50 V. During a test output

terminal voltage is displayed, together with flashing high voltage symbols,

and the flashing red LED.

TEST MODE SUMMARY

Insulation Resistance Testing (R)

This mode measures insulation resistance at the selected voltage to

provide an instantaneous spot reading. Final test result is given

sequentially with the corresponding leakage current and capacitance

value.

Test Current measurement (I)

This mode measures insulation at the selected voltage to provide an

instantaneous spot reading, but displays leakage current value on the

digital display. (N.B. The analogue scale always displays resistance). Final

test result is given sequentially with the corresponding resistance and

capacitance value.

Polarization Index Testing (PI)

Polarization Index is the term applied to the Dielectric Absorption ratio,

when the insulator is subjected to an insulation resistance test, and the

resistance values are measured after time T1 (Default 1 minute) and

again after time T2 (Default 10 minutes). Polarization Index is calculated

automatically from the resistance value after time T2, divided by the

resistance value after time T1. High dielectric absorption is indicated by

high PI ratio (see ‘Application of test Techniques’). Final test results

are given sequentially with the corresponding leakage current and

capacitance value. The test will run at any voltage. Custom timed ‘PI‘

values can be set if required (see ‘Custom timed PI test’ on page 12).

Dielectric Discharge Testing (DD)

This mode measures the dielectric absorption of an item under test while

ignoring the effects of parallel surface leakage paths. Default test time is 30

minutes followed by 1 minute discharge. Final test results are given

sequentially with a PI value, the final resistance value, and capacitance

value. Custom timed DD values can be set if required (see ‘Custom

timed DD test’).

FEATURES AND CONTROLS

Terminal Connection covers

Individually lifted to access test lead

terminals. Covers interlocked with

sliding recess cover.

Splashproof recess Cover Slides

back to reveal mains and 12V battery

charging connections together with

instrument protection fuses.

Voltage display

Test voltage or external voltage >50V,

together with flashing H.V. symbols. Condition and Warning

indicators

Flash to indicate any adverse

conditions affecting the test. Also

indicates when results of last test

are being sequentially displayed.

RS232C socket

Sends test results every 5 secs

to enable download to PC.

Display right hand cursor

Indicates selected Test mode.

Display left hand cursor

Indicates selected voltage, or the timer.

Battery capacity Indicator

Segments recede as battery is used.

Symbol flashes when battery charge

is excessively low.

Test Push

Press for at least 1 second to

initiate test and start Timer. Press

again to manually stop test.

Range Keys

1) Select test mode.

2) Adjust variable voltage.

3) Set timer. Max. 90 minutes.

Selector Keys

1) Set voltage

2) Set Timer

On/Off Button

Press to turn On /Off. (Wait a few

seconds for Automatic Calibration)

Timer display - Shows set test

duration and displays time elapsing

during test.

HV Warning - Flashes when a test

is in progress, or a hazardous voltage

is present.

General

It is advisable to fully charge the battery before the instrument is put into

service for the first time. Charging is carried out by external a.c. mains

supply, or by 12 V d.c. supply. A 12 V charging lead fitted with an

automotive cigar lighter plug is available for charging the battery from a

vehicle.Testing is inhibited during charging.

Mains supply re-charging

Mains input recharging requires a voltage within the range 95 - 265 V a.c.,

50 - 60 Hz. Disconnect the test leads and connect the mains supply to the

IEC 320 connector in the charging recess. Confirm that the red indicator

lamp is illuminated. Charging is automatic as soon as the mains supply is

connected. To fully recharge the battery takes about 16 hours. Eight hours

charging (from a fully discharged state) will achieve at least 90% of full

charge. Turn the instrument on and check the battery capacity indicator to

show the state of charge.

12 V d.c. supply re-charging

This method of re-charging should only be carried out if a mains supply is

unavailable as it is slower and less efficient. If using a vehicle as the

charging source, the engine should be running. Observing correct

polarities shown, connect the 12 V DIN socket to the external 12 V d.c.

supply and switch on.

Caution: Applying more than 15 V to this socket will overcharge the

battery.

12 V DIN socket (Viewed from front of panel)

Battery Charging Notes

1) Do not leave battery in a totally discharged state. Frequent

charging to keep the battery ‘topped up’ will maximise battery life.

2) Battery charging should be carried out in a dry environment

(the IP54 environmental protection applies with the charging

cover securely closed).

3) When charging the battery indoors, the area should be well

ventilated.

4) The battery should only be charged at temperatures in the range

0°C to 40°C.

5) It is beneficial to continue charging and no harm will occur to the

battery if the charger is left on indefinitely.

6) If the instrument is idle for long periods, recharge the battery for at

least 24 hours every 6 months. (More frequently if the storage

temperature is >40°C).

BATTERY CHARGING

Leave unconnected

Connect to +ve

Connect to -ve

FS1 Mains

Input

Fuse

Mains Input 12V d.c. Input

FS2 Guard

Fuse

OPERATION

Testing Precautions

1. The instrument must only be used by suitably trained and

competent persons.

2. Circuit connections must not be touched during a test.

3. The BM25 can give an electric shock. Highly capacitive circuits (e.g.

long lengths of cable) charged to several kV can create a potentially

lethal charge.

4. Care must be taken to prevent capacitive circuits becoming

disconnected during a test, leaving the circuit in a charged state.

5. The voltmeter and automatic discharge feature of the BM25 should

be regarded as additional safety features and not a substitute for

normal safe working practice.

6. When carrying out prolonged tests unattended, care should be

taken that no harm or damage can be caused.

7. When using the ‘BURN’ feature, care should be taken that no harm

or significant damage can be caused.

8. In certain circumstances, break-down of the circuit under test may

conceivably cause the instrument to terminate the test, possibly

causing a loss of display while the circuit remains energised. In

this event, the circuit must be discharged and the instrument

turned off before touching any connections.

GThe circuit under test must be completely de-energized

and isolated before test connections are made.

9. The BM25 has an environmental protection classification of IP54

with the charging recess cover securely closed. It is important from

a safety point of view (and to avoid unwanted leakage currents) to

ensure that the testing terminal area and the charging recess are

kept free from dirt and moisture.

10. Before use, any surface water on the instrument must be removed,

especially from the test lead sockets

11. Fuse replacements must be of the correct type and rating. Refer to

the Specification section for correct replacement fuse details.

12. If any part of the instrument is damaged, it should not be used, but

returned to the manufacturer or an approved repair company.

13. Should the plug on the power cord not be the type for your socket

outlets (receptacles), do not use an adaptor. Use a suitable

alternative mains cord. Wires in power cords are coloured as

follows:

U.K/International U.S.A.

Earth (Ground) Yellow/Green Green

Neutral Blue White

Phase (Line) Brown Black

6. Start a test by pressing the red test button for at least 1 second. The

flashing red LED and the flashing H.V. symbols warn that a test is

in progress.

7. When testing resistive or moderately capacitive loads (up to about

1 µF) the test voltage will appear within a few seconds. The test

voltage is controlled to within 5% of nominal, adjusting itself for

changes in resistance. The actual output voltage is displayed during

tests. On large capacitive items the voltage rise will be noticeably

slower and on low resistances (less than 10 MΩ) the voltage may

never rise to its nominal value.

8. Insulation resistance readings are updated once every second for

measurements up to about 100 MΩ. For measurements between

1 GΩand infinity the sample frequency rate will slow to 15

seconds.

9. A test can be manually aborted at any time by pressing the red test

button. A test will automatically terminate if:

- The set test duration is reached.

- The insulation under test suffers a complete breakdown.

- Excessive electrical noise interference (>2 mA at 5 kV).

- The battery becomes exhausted

- Fuse FS2 ruptures.

- An internal fault occurs.

When the test is terminated the item under test will be automatically

discharged.

10. To switch the instrument Off, press the On/Off button once. Auto

switch-off operates after 10 minutes inactivity in ‘R’ ‘I‘ and ‘Burn’

modes, and after 30 minutes inactivity in ‘DD’, ‘PI’ and ‘SV’

modes.

Performing Tests - General

1. Switch the BM25 On by pressing the ‘On/Off’ switch once. All LCD

segments appear for 5 seconds, then the word ‘CAL’ appears for

about 5 seconds. When the word ‘CAL’ disappears, the instrument

is ready for use, and in standby mode.

Note: When not testing (i.e. in standby mode) the BM25 acts as a

voltmeter. (50 V to 1000 V).

2. Ensure that all test leads are clean and in good condition, and

connect them to the isolated circuit under test. If an external

voltage >50 V is detected the voltage is displayed together

with high voltage symbols.

3. Select the required test mode using the Range keys to move the

right hand cursor.

4. Unless accepting a default test time, use the Selector keys to move

the left hand cursor to the timer position and increment to the

desired test duration using the Range keys. (Maximum test time

is 90 minutes).

5. Use the Selector keys again to set the required test voltage. The

variable voltage position gives the option to select a non-standard

voltage between 25 and 5000 V d.c., or to continuously vary the

voltage in 25 V steps during a test. To select, move the left hand

cursor to the variable voltage position and adjust the output

terminal voltage using the Range keys. The voltage set is shown at

the top of the display. When set to variable voltage, the test mode

cannot be altered.

Note: Changing the voltage during a test will temporarily alter the

reading. A steady reading will appear when the new voltage has been

stable over a full sample period (typically 5 seconds).

1. Using the ▲ ▼ Range keys move the right hand cursor to ‘I’, and

follow the same procedure as for Insulation Test ‘R’.

2. On completion, the final current leakage measurement is displayed

sequentially with the resistance and the capacitance value, where

available. This sequential display repeats until a key is pressed or

Auto switch-off operates. For more details of final display

information see Appendix 1.

Polarization Index and Dielectric Absorption Ratio Testing

When diagnostic testing insulation it is useful to investigate the way in

which the insulation reading varies with the time the test voltage has been

applied. One way is to compare the insulation resistance reading at two

different times dividing the later reading by the earlier reading. The result

is known as the Dielectric Absorption ration (DAR).

The normal appliaction of this is when the reading at 10 minutes is

divided by the resistance reading after 1 minute. this ratio is known as the

Polaristation Index (PI) of the sample.

The BM25 is capable of carrying out the more generalised DAR test and

the PI test automatically.

The BM25 uses 3 time settings when testing.

T3 Represents the total test duration. After this time period the BM25

will switch off the test current and discharge the sample under test.

T2 Represents the time of the second measurement requires to

evaluate a polarisation index and which must not be greated than

T3.

T1 Represents the time of the first measurement required to evaluate a

polarisation index.

OPERATION

Testing Procedures

Insulation Resistance Testing (R)

This test mode measures insulation resistance continuously at the selected

voltage. The highest digital readings obtainable are 500 GΩat 500 V and

5 TΩat 5000 V, above which the specified accuracy can be expected to

decline. However, the analogue indicator display functions to 1TΩat all

voltages.

1. Using the ▲ ▼ Range keys move the right hand cursor to ‘R’.

2. Accept the default time of 30 minutes, or using the ▲ ▼ Selector

keys move the left hand cursor to the position and then set the

test duration using the ▲ ▼ Range keys. Maximum test time is 90

minutes.

3. Using the ▲ ▼ Selector keys move the left hand cursor to the

required test voltage.

4. Start the test by pressing the red test button for at least one second.

5. On completion, the final resistance measurement is displayed

sequentially with the corresponding leakage current and the

capacitance value, where available. This sequential display repeats

until a key is pressed or Auto switch-off operates. For more details

of final display information see Appendix 1.

Test Current measurement (I)

This test mode measures insulation continuously at the selected voltage,

but displays leakage current value instead of resistance. This enables even

higher resistances to be calculated. Using this method it is theoretically

possible to measure resistance up to 500 TΩat 5000 V but it will be

necessary to perform an open circuit calibration test to establish

measurement circuit offset current and test lead leakage. (This is ±0,2 nA

at normal temperatures with new, clean test leads).

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