ABB REG670 Applications Manual page 169

1MRK 502 071-UEN -
3·Id
IEC05000176 V3 EN
Figure 64: Application of the1Ph High impedance differential protection HZPDIF function on a reactor
Generator protection REG670 2.2 IEC and Injection equipment REX060, REX061, REX062
Application manual
Setting example
It is strongly recommended to use the highest tap of the CT whenever
high impedance protection is used. This helps in utilizing maximum
CT capability, minimize the secondary fault, thereby reducing the
stability voltage limit. Another factor is that during internal faults, the
voltage developed across the selected tap is limited by the non-linear
resistor but in the unused taps, owing to auto-transformer action,
voltages much higher than design limits might be induced.
Section 7
Differential protection
IEC05000176-3-en.vsd
163