ABB Relion 670 Series Applications Manual page 531

1MRK 511 401-UEN Rev. K
CT 200/1
Star
CT 500/5
Star
IEC06000558 V1 EN-US
Figure 255: Star-star connected power transformer solutions
For this particular power transformer, the 110 kV side phase-to-earth no-load voltages are
exactly in phase with the 36.75 kV side phase-to-earth no-load voltages. Thus, when external
phase angle shift compensation is done by connecting main CTs in delta, both set of CTs must
be identically connected (i.e., either both DAC or both DAB as shown in the right-hand side in
Figure 255) in order to put 110 kV & 36.75 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 1 A CT inputs in the IED.
2. Check that LV CTs are connected to 5 A CT inputs in the IED.
3. Make sure that both CT sets are identically connected (i.e., either both side DAC or both
side DAB) when delta connected CTs are used.
4. For star connected CTs, make sure how they are star connected (i.e., earthed) towards or
away from the protected transformer.
5. Enter the settings for all three CT input channels used for the HV side CTs as shown in
Figure
Table 83: HV side CTs input channels
Setting parameter
CTprim
CTsec
CTStarPoint
6. Enter the settings for all three CT input channels used for the LV side CTs as shown in
Table
Bay control REC670
Application manual
31.5/31.5/(10.5) MVA
110±11×1.5% /36.75/(10.5) kV
YNyn0(d5)
255.
83.
© Copyright 2017 Hitachi Power Grids. All rights reserved
CT 200/1
in Delta
(DAB)
CT 500/5
in Delta
(DAB)
Selected value for solution 1 (star
connected CT)
200
1
FromObject
31.5/31.5/(10.5) MVA
110±11×1.5% /36.75/(10.5) kV
YNyn0(d5)
en06000558.vsd
Selected value for solution 2
(delta connected CT)
200
=
115
3
EQUATION1891 V1 EN-US
(To compensate for delta
connected CTs)
1
ToObject
Section 18
Monitoring
525