Summary And Conclusions - ABB REG670 Applications Manual

Section 7
Differential protection
7.1.4.4
146
To compensate for delta connected CTs, see equation 20.
7. Enter the following values for the general settings of the differential protection
function, see table 22
Table 22: General settings of the differential protection function
Setting parameter
RatedVoltageW1
RatedVoltageW2
RatedCurrentW1
RatedCurrentW2
ConnectTypeW1
ConnectTypeW2
ClockNumberW2
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 star or delta connected. However the IED has been designed with
the assumption that all main CTS are star 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 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.
Generator protection REG670 2.2 IEC and Injection equipment REX060, REX061, REX062
Selected value for both Solution 1
(star connected)
110 kV
36.75 kV
165 A
495 A
STAR (Y)
star=y
0 [0 deg]
On
On
No
No
Winding 1 (W1)
1
12
23
23
1.5%
Not relevant for this application.
Use default value.
1MRK 502 071-UEN -
Selected value for both Solution 2
(delta connected)
110 kV
36.75 kV
165 A
495 A
STAR (Y)
star=y
0 [0 deg]
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