ABB RELION 650 Series Applications Manual page 83

1MRK 504 158-UEN A
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 vector group 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 star-delta vector groups around the
world and provides information about the required type of main CT delta connection on the
star side of the protected transformer.
IEC vector group
YNd1
Dyn1
YNd11
Table continues on next page
Application manual
Positive sequence no-load
voltage phasor diagram
Y
IEC06000559 V1 EN-US
Y
IEC06000560 V1 EN-US
Y
IEC06000561 V1 EN-US
Required delta CT connection type on star side of the
protected power transformer and internal vector group
setting in the IED
DAC/Yy0
DAB/Yy0
DAB/Yy0
Section 6
Differential protection
77