ABB RET670 Applications Manual page 159

1MRK504116-UUS C
3·87
ANSI05000176 V2 EN
Figure 43: Application of the1Ph High impedance differential protection HZPDIF (87) function on an
autotransformer
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 current, 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
Section 3
IED application
ANSI05000176-2-en.vsd
153