ABB RET670 Applications Manual page 122

Section 3
IED application
116
CT 200/1
Wye
31.5/31.5/(10.5) MVA
110±11×1.5% /36.75/(10.5) kV
CT 500/5
Wye
ANSI06000558 V1 EN
Figure 29: Two differential protection solutions for wye-wye connected transformer.
For this particular power transformer the 110 kV side phase-to-ground no-load
voltages are exactly in phase with the 36.75 kV side phase-to-ground 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 29) 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 wye connected CTs make sure how they are 'star'red (that is, grounded) 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 33.
CT 200/1
in Delta
YNyn0(d5)
CT 500/5
in Delta
1MRK504116-UUS C
(DAB)
31.5/31.5/(10.5) MVA
110±11×1.5% /36.75/(10.5) kV
(DAB)
en06000558_ansi.vsd
Application manual
YNyn0(d5)