To compensate for delta connected CTs, see equation 20.7. Enter the following values for the general settings of the differential protectionfunction, see table 22Table 22:General settings of the differential protection functionSetting parameter Selected value for both Solution 1(star connected)Selected value for both Solution 2(delta connected)RatedVoltageW1 110 kV 110 kVRatedVoltageW2 36.75 kV 36.75 kVRatedCurrentW1 165 A 165 ARatedCurrentW2 495 A 495 AConnectTypeW1 STAR (Y) STAR (Y)ConnectTypeW2 star=y star=yClockNumberW2 0 [0 deg] 0 [0 deg]ZSCurrSubtrW1 On Off 1)ZSCurrSubtrW2 On Off 1)TconfigForW1 No NoTconfigForW2 No NoLocationOLT1 Winding 1 (W1) Winding 1 (W1)LowTapPosOLTC1 1 1RatedTapOLTC1 12 12HighTapPsOLTC1 23 23TapHighVoltTC1 23 23StepSizeOLTC1 1.5% 1.5%Other parameters Not relevant for this application.Use default value.Not relevant for this application.Use default value.1) Zero-sequence current is already removed by connecting main CTs in delta.7.1.4.4 Summary and conclusionsThe IED can be used for differential protection of three-phase power transformerswith main CTs either star or delta connected. However the IED has been designed withthe assumption that all main CTS are star connected. The IED can be used inapplications where the main CTs are delta connected. For such applications thefollowing shall be kept in mind:1. The ratio for delta connected CTs shall be set √(3)=1.732 times smaller than theactual individual phase CT ratio.2. The power transformer vector group shall typically be set as Yy0 because thecompensation for power transformer the actual phase shift is provided by theexternal delta CT connection.3. The zero sequence current is eliminated by the main CT delta connections. Thuson sides where CTs are connected in delta the zero sequence current eliminationshall be set to Off in the IED.Section 7 1MRK 502 071-UEN -Differential protection146 Generator protection REG670 2.2 IEC and Injection equipment REX060, REX061, REX062Application manual
