ABB REG670 Applications Manual page 148

Section 7
Differential protection
142
Setting parameter
LocationOLTC1
Other Parameters
1)
To compensate for delta connected CTs
2)
Zero-sequence current is already removed by connecting main CTs in delta
Delta-star connected power transformer without tap charger
Single line diagrams for two possible solutions for such type of power transformer
with all relevant application data are given in figure 56.
CT 400/5
Star
60 MVA
115/24.9 kV
Dyn1
(D Y)
AB
CT 1500/5
Star
IEC06000555 V1 EN
Figure 56: Two differential protection solutions for delta-star connected power
transformer
For this particular power transformer the 115 kV side phase-to-earth no-load voltages
lead by 30° the 24.9 kV side phase-to-earth no-load voltages. Thus when external
phase angle shift compensation is done by connecting main 24.9 kV CTs in delta, as
shown in the right-hand side in figure 56, it must be ensured that the 24.9 kV currents
are rotated by 30° in anti-clockwise direction. Thus, the DAB CT delta connection
(see figure 56) must be used for 24.9 kV CTs in order to put 115 kV & 24.9 kV currents
in phase.
Generator protection REG670 2.2 IEC and Injection equipment REX060, REX061, REX062
Select value for solution 1 (star
connected CT)
Not used
Not relevant for this application.
Use default value.
60 MVA
115/24.9 kV
Dyn1
(D
AB
CT 1500/5
1MRK 502 071-UEN -
Selected value for solution 2
(delta connected CT)
Not used
Not relevant for this
application. Use default value.
CT 400/5
Star
Y)
in Delta
(DAB)
en06000555.vsd
Application manual