Megger SVERKER 900 Montage- und Bedienungsanleitung

Application Note

Subject to change without notice. Printed matter No. ZR-CR03E Doc. CR033089BE V01 2015

SVERKER900

Relay and Substation Test System

Current transformer testing

This application note gives examples on how to

perform some typical tests on current transformers

(CTs) with SVERKER 900. These tests are common to

perform for instance during commissioning.

Important

Read and comply with the safety instruc-

tions in the User's manual.

Test procedures

Tests to be done at commissioning

▪Wiring check and visual inspection

▪Polarity test with DC current or AC voltage

▪Burden impedance test

▪Magnetization curve test

▪Primary injection test with load connected

Other tests

▪Secondary resistance test (RCT)

▪Primary injection - Ratio test with AC current or voltage

(no load connected)

Required equipment for testing

▪SVERKER 900

Wiring check and visual inspection

1] Check that the primary and secondary side

are connected for correct ratio according to

system requirements.

2] Check the tightness for secondary connec-

tions, including grounding and shorting links.

3] Check that each core is connected to correct

load according to drawings.

4] Check that each core are grounded in only

one point on secondary side and close to

CT location. For CT secondaries connected

together the grounding shall be done at

relay point, for exampel cores connected to

differential protection.

Current transformer data

Relay core 5P and 10P

Measuring core 0.3 B

nAccuracy limit factor (ALF) for relay cores

Safety factor (SF) for measuring cores

2SVERKER900 ZR-CR03E CR033089BE

Polarity test with

DCcurrent

Polarity test is made to conﬁrm the polarity mark-

ing on the CT (primary and secondary) and verify it

is matching with the drawing. This is very important

when it comes to directional and differential protec-

tions.

To reduce the amount of connection changes the po-

larity test can be done with voltage (AC) if knee-point

is known or after CT-magnetization. See "Polarity test

with voltage (AC).

1] Isolate the CT secondary from the load and

make connections as shown in the ﬁgure

below.

Note Core(s) not included in test should be shortcir-

cuited.

2] Select I-gen for individual conﬁguration.

Note If higher current is needed to get a read-

able value on VAM-meter, change to parallel

conﬁguration.

3] Select I1 on and set "0" in frequency ﬁeld to

get DC current.

4] Set DC current to a value about 5-10% of

primary CT current.

5] Set the VAM-meter for "DC" current measur-

ing and activate the "Hold on stop" function.

6] Make a short (1 sec) run/stop and check that

the value is positive.

CR033089BE ZR-CR03E SVERKER900 3

7] Reverse connection on P1 and P2 and check

that the value is negative for current.

8] Repeat test for all phases and cores.

Note Only make one test for each direction at a

time.

Test values including hold values are saved individually

in a test ﬁle. See "Test ﬁle management" in the User's

manual.

Secondary resistance test

(RCT)

Secondary resistance test is made to verify continuity

and the value is used for calculating knee-point.

1] Connect according to picture below.

2] Set current to be generated into secondary

side of CT. A recommended value is 10% of

In (1 A or 5 A).

3] Set the VAM-meter for "DC" voltage measur-

ing and activate the "Hold on stop" function.

4] Make the same for current, see "Polarity test

with DC current".

4SVERKER900 ZR-CR03E CR033089BE

5] Inject current until stabilized value is ob-

tained on voltage and current meters.

6] Read the result and calculate the resistance

value.

7] Repeat test for all phases and cores.

Test values including hold values are saved individually

in a test ﬁle. See "Test ﬁle management" in the User

manual.

Note If no magnetization curve is to be veriﬁed

always make a short AC injection manually.

See "Demagnetization" on page 7

Magnetization curve test

A magnetization curve test is made to conﬁrm the

magnetization characteristics of a CT.

This test shall be conducted before ratio test and after

secondary resistance and polarity test, since residual

magnetism left in the core after DC test (polarity,

resistance) otherwise gives error in the ratio test.

1] Calculate the knee-point level along with the

formulas:

Protection

core

Vslv=Is * ALF (Rct + (VA/Is2))

Measuring

core

Vslv=Is * FS (Rct + (VA/Is2))

Where:

Is Rated secondary current

Rct CT secondary resistance

VA Rated CT burden

ALF Accuracy Limit Factor

Fs Safety factor

2] Select conﬁguration, parallel or series, of

U-gen depending on calculated knee point

level.

3] Connect as shown below when starting CT-

magnetization instrument.

The primary of the CT should be open during

test.

CR033089BE ZR-CR03E SVERKER900 5

Magnetization test

The magnetization test can be made manual or in

auto mode.

Manual test

1] Press and turn the knob according to

arrow symbol. Continue until arrow change

direction.

2] Now turn the knob anticlockwise (at approxi-

mately the same speed as you increased) to

start decreasing the voltage down to zero.

Tip Points can be plotted by pressing the

knob.

Automatic mode

1] Press the knob symbol to change to auto.

2] Press and the curve will be automati-

cally plotted.

3] Repeat test for all phases and cores.

A voltage and current limit can be set

, . This can be useful in:

A] Manual mode to prevent too high injection.

B] Automatic mode if a higher end value (A) is

wanted.

6SVERKER900 ZR-CR03E CR033089BE

Polarity test with AC voltage

Polarity test

1] Connect according to picture below.

With this connection the angle between voltage and

current for secondary side are measured. (see picture

below)

2] Set voltage and current for VAM-meter to

"Hold on stop".

3] Press twice to display angle value.

4] Press to start the test.

5] Press on voltage parameter. When it turns

yellow, slowly turn knob clockwise to in-

crease voltage.

6] Generate 50% of knee-point voltage,

Wait for angle to stabilize and then press

7] Note the angle value to compare with next

test.

Note After interrupted magnetization always do a

demagnetization and shortly ground primary

and secondary side of CT.

8] Make the same test for the connection be-

low, the VAM-meter should show the same

value.

9] Change connection on CT secondary side, see

below.

10] Make the same test and check that the angle

has changed with 180 degree.

Ratio test with AC voltage

1] In same test connection as above, press

twice and read the voltage value.

For voltage injection on CT,s the ratio is in-

verted S/P=R.

In this case S=12V , P=1,2V , R=10

CR033089BE ZR-CR03E SVERKER900 7

Demagnetization

1] Connect according to picture below.

2] Press to start the test.

3] Press on voltage parameter. When it turns

yellow, slowly turn knob clockwise to in-

crease voltage.

4] Generate up to knee-point voltage and then

slowly turn knob anticlockwise down to zero.

Burden impedance test

A burden test is made to ensure that the load (VA) is

not more than speciﬁed on nameplate.

1] Connect according to picture below.

2] Inject current into the burden loop. A recom-

mended value is 100% of In (1 A or 5 A).

3] Set the VAM-meter for "AC" voltage measur-

ing and activate the "Hold on stop" function.

4] Make the same for current.

8SVERKER900 ZR-CR03E CR033089BE

5] Inject current until stabilized value is ob-

tained on voltage and current meters.

6] Repeat test for all phases and cores.

Test values including hold values are saved individually

in a test ﬁle. See "Test ﬁle management" in the User

manual.

Note High impedance relays shall be shorted during

the burden impedance test

7] To see values for R, X and Z press two times

on right arrow.

Ratio test - Primary

injection no load

connected

This test is to verify the turns ratio of the CT.

1] Make connections as shown in ﬁgure below.

Note CT-cores not included in test should be

shorted.

2] Select I-gen for parallel conﬁguration.

3] Set the current in VAM-meter for "AC" and

press for"Hold on stop".

4] Inject on primary side of CT a current of mini-

mum 10% of the rated primary current.

CR033089BE ZR-CR03E SVERKER900 9

5] Check that the obtained turns ratio match

with rated on the nameplate.

6] Repeat test for all phases and cores.

Primary injection test –

with load connected

This test is to ensure the CT circuits are properly con-

nected with respected cores and there is no mix up

in the circuit (phase identiﬁcation). The ratio test can

also be done here.

Note High impedance relays shall be shorted during

the primary injection test.

1] Check that all links are closed in secondary

circuits for all cores included in test.

2] Single point grounding shall be veriﬁed for

CT circuits, before starting this test.

3] Start injection, between L2 phase and earth,

at zero current and slowly increase current.

Measure in phase L2 for all cores that cur-

rent is ﬂoating and then continue to 10% of

rated primary current.

4] Measure secondary current at all points of CT

circuits (protections and measuring devices).

5] Repeat test for connection L1-L2 and L2-L3,

see ﬁgures below.

Note Secondary current should only be observed

at respective phase and neutral leads during

phase to earth injection.

Secondary current should only be observed at

respective phases and no current on neutral

during phase to phase injection.

10 SVERKER900 ZR-CR03E CR033089BE

Connection L1-L2

Connection L2-L3

Core identiﬁcation

When one CT has several cores used for different

purposes the cores can be identiﬁed during primary

injection test.

1] Inject 10% of rated primary current between

phase to earth (ground) with all burdens

connected.

2] Short one of the cores at the CT terminal.

3] Check that the current to the connected load

has been considerable lower or zero.

4] Make the same veriﬁcation for the other

cores.

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