ABB Relion 670 Series Applications Manual page 529

1MRK 511 401-UEN Rev. K
CT 400/5
60 MVA
115/24.9 kV
Dyn1
(D Y)
AB
CT 1500/5
IEC06000555 V1 EN-US
Figure 254: Delta-star connected power transformer solutions
For this particular power transformer, the 115 kV side phase-to-earth no-load voltages lead the
24.9 kV side phase-to-earth no-load voltages by 30 degrees. Thus, ensure that the 24.9 kV
currents are rotated by 30° in the anti-clockwise direction when external phase angle shift
compensation is done by connecting main 24.9 kV CTs in delta (as shown in
hand side). Therefore, the DAB CT connection must be used for 24.9 kV CTs in order to put 115
kV & 24.9 kV currents in phase.
In order to ensure proper application of the IED for this power transformer, proceed as
follows:
1. Ensure that HV & LV CTs are connected to 5 A CT inputs in the IED.
2. For the second solution, make sure that LV delta connected CTs are DAB connected.
3. For star connected CTs, make sure how they are star connected (i.e., earthed) to/from
the protected transformer.
4. Enter the settings for all three CT input channels used for the HV side CTs as shown in
Table
Table 80: HV side CTs input channels
Setting parameter
CTprim
CTsec
CTStarPoint
5. Enter the settings for all three CT input channels used for the LV side CTs as shown in
Table
Bay control REC670
Application manual
Star
Star
80.
81.
© Copyright 2017 Hitachi Power Grids. All rights reserved
CT 400/5
Star
60 MVA
115/24.9 kV
Dyn1
(D Y)
AB
CT 1500/5
in Delta
(DAB)
Selected value for both solutions
400
5
ToObject
Section 18
Monitoring
en06000555.vsd
Figure 254, right-
523