Description
2.3 Protection system
3WA Air Circuit Breakers
44 Equipment Manual, 05/2021, 92310000002-03
2.3 Protection system
2.3.1 General description of function
The protection system of the 3WA circuit breaker consists of:
• Current sensors for measurement
The current sensors installed in the 3WA circuit breaker feature a Rogowski coil and an
energy core. The measured signal is provided by the Rogowski coil.
The Rogowski coil is used as a component in electronic measuring devices to measure
alternating current. It is a toroidal coil without a ferromagnetic core and can detect small
operational currents as well as large short-circuit currents linearly and with very high
accuracy.
• Optional voltage tap at the main circuits, including voltage tap module for voltage
measurement
The optional internal voltage tap is implemented at the lower or upper main circuits.
The voltage is prepared by the voltage tap module and made available to the electronic
trip unit for evaluation.
The voltage tap module is available in two versions, see Chapter Voltage tap module VTM
(Page 316).
• Electronic trip unit
The electronic trip unit is controlled by a microprocessor and operates independently of an
auxiliary voltage. It enables systems to be adapted to the different protection
requirements of distribution systems, motors, transformers and generators. In order to
enable a quick adaptation to new grid conditions on site, the electronic trip unit has been
developed with consistent focus on modularity.
Among other things, the following functions can be added easily and at any time:
– Ground-fault protection
– Changing the current rating
– Communication
– Metering function
Depending on the configuration, the electronic trip unit has various protective functions
which evaluate the measured currents and voltages and compare them with the
parameterized settings. If a measured value exceeds the set threshold, the circuit breaker
is tripped with a delay or instantaneously.
The electronic trip unit is powered (self-acting) by the internal current sensors, or
optionally via the voltage tap of the metering function.
• Tripping solenoid to control the mechanical system of the circuit breaker
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