User Manual

Description
2.3 Protection system
3WA Air Circuit Breakers
58 Equipment Manual, 05/2021, 92310000002-03
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 Hi-Z 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 voltage transformers 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 independently operating ground-fault protection functions are available to the user.
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.
Note
The maximum voltage at the measuring input of the electronic trip unit is 150 V rms. This
must not be exceeded. A varistor or other suitable voltage limitation device must be
connected in parallel to the load for this reason.
The ETU600 LSIG Hi-Z electronic trip unit can differentiate between an infeed-side ground
fault and an outgoing-side ground fault. In countries where British standards are used, the
areas before and after the circuit breaker are referred to as the “restricted zone” and
“unrestricted zone” respectively. Derived from this, this type of ground-fault protection is
called “Restricted Earth Fault (REF)” and “Unrestricted Earth Fault (UREF)”.
Please note that ground-fault protection with ETU600 LSIG Hi-Z differs from high-resistance
neutral point grounding and must not be confused with it.