User Manual

Description
2.3 Protection system
3WA Air Circuit Breakers
Equipment Manual, 05/2021, 92310000002-03
57
GF Direct
The ground-fault current is measured directly, e.g. in the cable of the transformer neutral
point, with a current transformer. Commercially available measuring transformers with
primary rated current I
pr = 150 A to 2000 A and secondary rated current Isr = 1 A can be used
for this purpose.
GF Dual
With the setting GF Dual, the acquisition methods GF Residual (calculation of the vectorial
sum of the currents) and GF Direct (direct measurement of the ground-fault current with an
external current transformer) can be used simultaneously. This provides the user with two
independent characteristics for ground-fault protection.
In this GF mode, the ETU600 LSIG electronic trip unit is able to distinguish an infeed-side
ground fault from an outgoing-side ground fault. The ground fault on the outgoing side can
be interrupted with the circuit breaker. When a ground fault is detected on the infeed side,
the ETU600 LSIG electronic trip unit can issue a signal to open the upstream medium-voltage
circuit breaker.