16
Siemens · 10/2014
General data
3WL Air Circuit Breakers
3WL air circuit breakers/non-automatic air circuit breakers up to 6300 A (AC), IEC
Electronic Trip Units (ETU)
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.
Communication capability
The international standardized PROFIBUS DP or MODBUS can
be used to transmit data such as current values, switching
states, causes of tripping etc. to central computers.
Data acquisition and energy management are possible in
conjunction with the metering function Plus.
An internal circuit breaker data bus allows switchboard
panel communication between the circuit breaker and typical
secondary devices in the circuit breaker section:
• Control of analog displays
• Facility to test the communication build-up with circuit
breakers
• Display of tripping state and tripping reasons
• Input module for reading in further switchgear panel signals
and for transmission of these signals to the PROFIBUS DP
or MODBUS
• Various output modules for displaying measured values
This means that it is not only possible to monitor the device
remotely, but also to transmit current values from the entire
system and perform switching operations remotely.
I
2
t and I
4
t characteristic curves for overload protection
The best protection for the whole switchgear is achieved by
setting the tripping characteristic curve to an optimum value.
In order to achieve optimal discrimination for upstream fuses
or medium voltage protection systems, the inclination of the
characteristic curve can be selected for the overload range.
The overload protection L (long time protection) for the ETU45B
and ETU76B Electronic Trip Units allows the curve to be
switched between
I
2
t and
I
4
t characteristics.
The
I
4
t characteristic improves discrimination for downstream
circuit breakers and fuses.
Electronic Trip Units ETU
Modularity has also been strictly emphasized during the
development of the Electronic Trip Units. These are some of
the modules which can be easily retrofitted at any time:
• Ground-fault protection module
• Communication
• Metering function
•Display
• Rated current module (rating plug)
This allows quick adaptation to new local mains conditions. In
addition, innovative functions have been included in the ETUs.
Rated current module / rating plug
The rated current module is an exchangeable module which
allows the user to reduce the rated device current so as to
adapt it optimally to the plant; e.g. if a new plant section is put
into operation. The rated current module must be selected to
correspond to the rated current of the plant.
Example of configuration for ETU45B
Metering function Plus
Selectable parameters
In the case of quick changes of power supply conditions,
e.g. for switchover from transformer to generator operation
or if a section of the supply is disconnected when the shift
changes, 3WL circuit breakers allow the relevant protection
parameters to be quickly adapted to the new conditions.
The ETU76B contains two independent tripping characteristics
(parameter sets). The switchover is completed within 200 ms
and is performed with the help of an external signal.
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