Description
2.3 Protection system
3WA1 air circuit breaker
Equipment Manual, 02/2023, 92310000002-06
61
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 2 independent characteristics for ground-fault protection.
In this GF mode, the ETU600 LSIG electronic trip unit can detect an infeed-side ground
fault and 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
on terminals X8-11 and X8-12 of the circuit breaker, the electronic trip unit outputs a
signal. This must be integrated in the control in order to open the upstream medium-
voltage circuit breaker.
2.3.5.8 Ground-fault protection GF Hi-Z
In addition to the GF modes mentioned in the Chapter "Ground-fault protection GF", the
3WA circuit breaker with the ETU600 LSIG Hi-Z electronic trip unit offers the possibility
of connecting a current transformer combination for ground-fault protection between the
transformer and the circuit breaker. The current transformer combination consists of
several current transformers.
The GF Hi-Z ground-fault protection is only available with the ETU600 LSIG Hi-Z
electronic trip unit. This was specially developed for the detection of ground-fault
currents on the infeed side of the circuit breaker. The ETU600 LSIG Hi-Z provides the
necessary inputs for connecting the current transformers and resistor required for this
application. This makes it possible to dispense with the protection relay which would
otherwise be required for protection between the transformer and the circuit breaker.
The ETU600 LSIG Hi-Z takes over this task completely.
Two independent ground-fault protection functions are available to the user, the first
one toward the transformer and the second one toward the load side.
For this purpose, commercially available Class TPS current sensors, which are
interconnected in a group and connected in parallel via a high-resistance load resistor,
are connected to terminals X8-11 and X8-12 of the secondary disconnect terminal of the
circuit breaker.
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