CT scaling example
The connection of CTs to the IED measurement inputs and the ratings of the current transformers and
load nominal current are as in following gure.
Figure. 5.2.1. - 3. Example connection.
Initial data of the connection and the ratings are presented in following table.
Table. 5.2.1. - 4. Initial data from example connection.
Phase current CT:
CT primary 100A
CT secondary 5A
Ring core CT in Input I02:
I0CT primary 10A
I0CT secondary 1A
Load nominal 36A
Phase currents are connected to summing “Holmgren” connection into the I01 residual input.
Phase current CT secondary currents starpoint is towards the line.
For the scaling of the currents to per unit values for the protections selection needs to be made now if
the protected object nominal current or the CT primary value should be the base for per unitizing.
If the per unit scaling is wanted to be according to the CT values then “Scale meas to In” is set to “CT
nom p.u.” As presented in the gure below.
AQ-F255
Instruction manual
Version: 2.00
© Arcteq Relays Ltd
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