Description
2.3 Protection system
3WA1 air circuit breaker
60 Equipment Manual, 02/2023, 92310000002-06
GF mode
A ground-fault current can be calculated mathematically or measured directly. The 3 GF
modes available on the ETU600 electronic trip unit are described below.
GF Residual
The ground current is formed by the vectorial sum of the currents measured with the
internal current sensors and the external N-conductor sensor (N-CT). All four-pole
circuit breakers have an internal N conductor sensor.
External N-conductor sensor (N-CT)
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 I
sr
= 1 A can be
used for this purpose.
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