High voltage side CT:
CT primary 800A
CT secondary 2A
HV-side nominal current:
669A
Ring core CT in Input I02:
3I0CT primary 250A
3I0CT secondary 1A
Low voltage side CT:
CT primary 8000A
CT secondary 5A
LV-side nominal current:
5888A
Both CTs are pointing through the transformer (HV-S2 and LV-S2 are pointing to same direction).
The nominal currents on high voltage and low voltage side are exactly the same as in application 1.
The only difference is that the secondary current level of the CTs have been changed to 2A on high
voltage side and to 5A on low voltage side. Nominal currents are still calculated the same way:
Per unit values for high –and low voltage side nominal currents can be calculated as shown below:
To multiply the per unit value with Phase CT secondary side current, it is possible to get the nominal
secondary current of transformer as Amperes. This current can be used when the unit is
commissioned and the directions of CTs are checked. In application 2 it is necessary to inject higher
amplitudes to the CTs via secondary injection tool to reach the nominal currents. See an example
calculation below:
Settings
Table. 5.2.1. - 6. Settings of the Phase CT scaling
Name
Range
Step Default
Description
Scale
meas to In
0:CT
nom
p.u.
1:Object
In p.u.
-
0:CT
nom
p.u.
Selection of the IED per unit system scaling reference, either the set phase
current CT primary or protected object nominal current. (NOT APPLICABLE IN
MACHINE PROTECTION).
Phase CT
primary
1…
5000.0A 0.1A
100.0A
Rated primary current of the CT in amperes.
Phase CT
secondary
0.2…
10.0A
0.1A
5.0A
Rated secondary current of the CT in amperes.
AQ-T257
Instruction manual
Version: 2.00
19
© Arcteq Relays Ltd