Electronic Trip Unit Etu - Siemens SENTRON 3WL10 Series Manual

2.4

Electronic trip unit ETU

As a protection device, the circuit breaker has the task of protecting installations and clearing
electrical faults occurring in the system. Whether a fault occurs is detected by a trip unit,
which compares the protection parameters set in it with the measured values. The 3WL10
air circuit breaker has a microprocessor-controlled trip unit.
The tripping characteristic can be adjusted to the required values with numerous possible
settings.
Selective tripping and instantaneous release
On short-circuits in the medium current range, selective tripping (ST) is ensured. On short-
circuits with a larger current and high arc energy in the arc chute, an instantaneous release
(INST) responds and interrupts the overcurrent immediately (< 30 ms).
Current-carrying circuit breaker
Air circuit breakers of the 3WL range are designed as current-carrying circuit breakers. Their
place in the power distribution is upstream of molded case circuit breakers and they must
have time-selective current-carrying characteristics. They are equipped with ST releases for
short-time-delayed short-circuit protection. The INST release for instantaneous short-circuit
protection can be disabled in certain circumstances.
The air circuit breakers can carry the full short-circuit current for a certain duration without
the contacts lifting and limiting the short-circuit current. This gives lower-level devices
enough time to disconnect the outgoing feeder with the fault.
Selectivity
Switching devices connected in series, e.g. circuit breakers and fuses, can work together in
a selective or discriminating manner to ensure graded tripping in the event of a fault. The
upstream switching device closest to the fault must trip in the event of a short-circuit. The
other switching devices in the circuit remain closed. This minimizes the effects of a fault in
terms of its duration (selectivity) and the area affected.
Air circuit breaker 3WL10
Manual, 11/2017, L1V30499596002-01
Short-circuit location
Description
2.4 Electronic trip unit ETU
33