Example of zero sequence CT scaling
Zero sequence CT scaling (ZCT scaling) is done when a zero sequence CT instead of a ring core CT is
part of the measurement connection. In such a case the zero sequence CT should be connected to the
I02 channel which has lower CT scaling ranges (see the image below).
Figure. 5.2.1 - 59. Connections of ZCT scaling.
Troubleshooting
When the measured current values differ from the expected current values, the following table offers
possible solutions for the problems.
NO
NOTE!
TE!
If you work with energized CTs, extreme caution needs to be taken when checking the
connections! An opened CT secondary circuit may generate dangerously high voltages. A
"buzzing" sound from the connector can indicate an open circuit.
Problem
Solution
The measured current
amplitude in all phases
does not match the
injected current.
The scaling settings may be wrong, check that the settings match with the connected current
transformer (
Measurement
→
Transformers
→
Phase CT scaling). Also check that the "Scale meas.
to In" is set accordingly. If possible, check the actual CTs and their ratings as there may have been a
need to change the original plan.
The measured current
amplitude does not
match one of the
measured phases./
The calculated I0 is
measured even though
it should not.
Check the wiring connections between the injection device or the CTs and the relay.
A
AQ
Q-M215
-M215
Instruction manual
Version: 2.04
58