Siemens SENTRON 3WA1 - Protection System; General Description of Function

Description
2.3 Protection system
3WA1 air circuit breaker
Equipment Manual, 02/2023, 92310000002-06
45
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 measuring 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 with very high
accuracy.
• Optional voltage tap at the main conducting paths, including voltage tap module
for voltage measurement
The optional internal voltage tap is implemented at the lower or upper main
conducting paths.
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 2 versions, see Chapter Voltage tap module
VTM for ETU600 (Page 351).
• 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. These protective functions
– evaluate the measured currents and voltages and
– compare the measured currents and voltages with the parameterized setting
values
If a metering 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