Megger SVERKER 900 Installation and operating instructions

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.