User Manual

Description
2.3 Protection system
3WA Air Circuit Breakers
Equipment Manual, 05/2021, 92310000002-03
55
2.3.5.7 Ground-fault protection GF
The ground-fault protection detects residual currents between the conductors and grounded
parts of the power distribution system. The ground-fault protection function responds when
the ground-fault current exceeds the set tripping current I
g for the set delay time tg.
Ground-fault protection can be implemented either as a current-independent or a current-
dependent function.
The ETU600 electronic trip unit with the option plug LSIG GFx has a current-independent or
current-dependent characteristic curve with the following characteristics for ground-fault
protection:
• I
2
t
• I
4
t
• I
6
t
In the case of a current-independent characteristic curve, the circuit breaker trips when the
tripping current is exceeded after the set delay tg. In the case of a current-dependent
characteristic, the circuit breaker trips according to the inverse-time characteristic.
Characteristic
Implementation on the circuit breaker
For direct measurement of the ground-fault current, an external current sensor (GF-CT) can
be connected to terminals X8-11 and X8-12 of the secondary disconnect terminal of the
circuit breaker.
The current sensor must have the following properties:
• Primary rated current I
pr = 150 A to 2000 A
• Secondary rated current I
sr = 1 A
• Accuracy class 1