Siemens SENTRON 3VL series - Use in motor protection

Application planning
5.6 Use in motor protection
3VL IEC molded case circuit breakers
64 System Manual, 11/2013, 110 0110 - 02 DS 03
5.6
Use in motor protection
The overload and short-circuit releases are designed for optimal protection and direct
starting of three-phase AC squirrel-cage motors. The molded case circuit breakers for motor
protection are sensitive for phase failures and have an adjustable trip class.
The ETUs operate with a microprocessor.
Note
The 3VL circuit b
reakers with motor protection function are suitable for use in IE2 motors.
You can obtain detailed information for the use of the 3VL molded case circuit breaker with
IE3 motors on request.
Operating principle of the overcurrent releases
The tripping characteristic curves of the inverse-time delayed overload releases are specially
designed for overload protection of 3-phase AC motors.
With the inverse-time delayed overload release "L", the value I
R
can be set to be 0.4 to 1.0
times the rated current I
n
of the molded case circuit breaker. This occurs in 0.01 increments
(e.g. 0.40 / 0.41 / 0.42 ... 0.99 / 1.0 x I
n
), so that the molded case circuit breaker exactly
matches the rated current of the motor to provide optimal protection.
The current transformers in the 3VL molded case circuit breaker not only measure the load
current, they also supply power to the electronic trip unit. No external auxiliary power supply
is required.
This independence from an external energy supply guarantees a high standard of safety.
Area of application
Machine tools, manufacturing systems, presses, fans, air-conditioning units and packaging
machines all require motors that must be protected. This is the main area of application of
the 3VL molded case circuit breakers for motor protection.
Trip class
The 3VL molded case circuit breakers offer the option of selecting from various trip units with
fixed or adjustable trip classes that are suitable for differing motor applications.
ETU 10 M
This version is equipped with a thermal image, phase failure sensitivity and the fixed trip
class 10.
ETU 30 M
This version is equipped with an adjustable trip class 10 to class 30 in addition to the thermal
image and phase failure sensitivity.