ABB Relion 670 Series Applications Manual page 128

Section 7
Differential protection
3·Id
IEC05000165 V2 EN-US
3·Id
IEC05000739 V2 EN-US
Figure 53: The protection scheme utilizing the high impedance function for the T-feeder
Normally this scheme is set to achieve a sensitivity of around 20 percent of the used CT
primary rating so that a low ohmic value can be used for the series resistor.
122
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1MRK 511 401-UEN Rev. K
IEC05000165-2-en.vsd
IEC05000739-2-en.vsd
Bay control REC670
Application manual