ABB Relion 670 Series Applications Manual page 120

Section 6
Differential protection
87
ANSI05000165 V1 EN-US
3·87
ANSI05000739 V2 EN-US
Figure 48: 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.
114
1MRK 511 358-UUS A
en05000165_ansi.vsd
ANSI05000739-2-en.vsd
Application manual