ABB Relion 670 Series Applications Manual page 527

1MRK 511 401-UEN Rev. K
CT 300/5
20.9 MVA
69/12.5 kV
YNd1
(YD
AC
CT 800/5
Star
IEC06000554 V1 EN-US
Figure 253: Star-delta connected power transformer solutions
For this particular power transformer, the 69 kV side phase-to-earth no-load voltages lead the
12.5 kV side phase-to-earth no-load voltages by 30 degrees. Thus, ensure that the HV currents
are rotated by 30° in the clockwise direction when external phase angle shift compensation is
done by connecting main HV CTs in delta (as shown in
the DAC delta CT connection must be used for 69 kV CTs in order to put 69 kV & 12.5 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 HV delta connected CTs are DAC 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 LV side CTs as shown in
Table
Table 77:
Setting parameter
CTprim
CTsec
CTStarPoint
5. Enter the settings for all three CT input channels used for the HV side CTs as shown in
Table
Bay control REC670
Application manual
Star
)
77.
LV side CTs input channels
78.
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CT 300/5
in Delta
(DAC)
20.9 MVA
69/12.5 kV
YNd1
(YD )
AC
CT 800/5
Star
Figure 253, right-hand side). Therefore,
Selected value for both solutions
800
5
ToObject
Section 18
Monitoring
en06000554.vsd
521