ABB RET670 Applications Manual page 124

Section 3
IED application
118
Setting parameter
ZSCurrSubtrW1
ZSCurrSubtrW2
TconfigForW1
TconfigForW2
LocationOLT1
LowTapPosOLTC1
RatedTapOLTC1
HighTapPsOLTC1
TapHighVoltTC1
StepSizeOLTC1
Other parameters
1)
Zero-sequence current is already removed by connecting main CTs in delta.
Summary and conclusions
The IED can be used for differential protection of three-phase power transformers with
main CTs either wye or delta connected. However the IED has been designed with the
assumption that all main CTS are wye connected. The IED can be used in applications
where the main CTs are delta connected. For such applications the following shall be
kept in mind:
1. The ratio for delta connected CTs shall be set √(3)=1.732 times smaller than the
actual individual phase CT ratio.
2. The power transformer phase-shift shall typically be set as Yy0 because the
compensation for power transformer the actual phase shift is provided by the
external delta CT connection.
3. The zero sequence current is eliminated by the main CT delta connections. Thus
on sides where CTs are connected in delta the zero sequence current elimination
shall be set to Off in the IED.
The following table summarizes the most commonly used wye-delta phase-shift
around the world and provides information about the required type of main CT delta
connection on the wye side of the protected transformer.
Selected value for both Solution 1
(wye connected)
On
On
No
No
Winding 1 (W1)
1
12
23
23
1.5%
Not relevant for this application.
Use default value.
1MRK504116-UUS C
Selected value for both Solution 2
(delta connected)
1)
Off
1)
Off
No
No
Winding 1 (W1)
1
12
23
23
1.5%
Not relevant for this application.
Use default value.
Application manual