ABB REG670 - Page 151

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 (that is, either both DAC or both
DAB as shown in the right-hand side in figure
57) in order to put 110 kV & 36.75 kV
currents in phase.
To ensure proper application of the IED for this power transformer it is necessary to
do the following:
1. Check that HV 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. When delta connected CTs are used make sure that both CT sets are identically
connected (that is, either both DAC or both DAB).
4. For star connected CTs make sure how they are 'star'red (that is, earthed) towards
or away from the protected transformer.
5. Enter the following settings for all three CT input channels used for the HV side
CTs, see table 20.
Table 20: CT input channels used for the HV side CTs
Setting parameter
Selected value for both solution 1
(star connected CTs)
Selected value for both Solution 2
(delta connected CTs)
CTprim 200
200
115
3
=
EQUATION1891 V1 EN (Equation 19)
CTsec
1 1
CTStarPoint FromObject ToObject
To compensate for delta connected CTs, see equation 19.
6. Enter the following settings for all three CT input channels used for the LV side CTs
Table 21: CT input channels used for the LV side CTs
Setting parameter
Selected value for both Solution 1
(star connected)
Selected value for both Solution 2
(delta connected)
CTprim 500
500
289
3
=
EQUATION1892 V1 EN (Equation 20)
CTsec
5 5
CTStarPoint ToObject ToObject
1MRK 502 071-UEN - Section 7
Differential protection
Generator protection REG670 2.2 IEC and Injection equipment REX060, REX061, REX062 145
Application manual