Description
2.3 Protection system
3WA1 air circuit breaker
50 Equipment Manual, 02/2023, 92310000002-06
2.3.5 Description of the protective functions
2.3.5.1 General description
Depending on the electronic trip unit and the options selected, the following protective
functions are available:
• Long time LT
• Short time ST
• Instantaneous short-circuit protection INST
• Neutral protection N
• Ground-fault alarm
• Ground-fault protection GF
• Ground-fault protection GF Hi-Z
• Directional short time dST
• Reverse power protection RP
• Enhanced protective functions EPF
For the ETU600 electronic trip unit, all of the protective functions can generally be set to
the "closed, ON" or "open, OFF" operating modes.
In the appendix Device numbers according to IEEE standard C37.2 (Page 562), the
device numbers (ANSI code) assigned according to IEEE standard C37.2 are given.
2.3.5.2 Long time LT
The overload protection is current-dependent and long-time delayed. It is based on the
rms value of the current and protects cables, busbars and busway systems in the event
of overload.
The overload protection is implemented independently for each phase and is equipped
with a thermal memory. This stores the circuit breaker's thermal state as determined by
the operational current and shortens the tripping time when reclosing following a trip.
The overload protection delay is defined at 6 times the current setting I
r
. The minimum
tripping time is limited to 500 ms.
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