Conventional motor circuit breakers are
commercially available for various
applications with different trigger
characteristics (L, G/U, R and K), as shown
in the diagram on the right. As frequency
inverters in most cases are used for
supplying motors which are classified as
operating equipment with very high starting
currents, only the K characteristic was
realized in this function.
Unlike the operation of a conventional motor
circuit breaker which disconnects the
equipment to be protected immediately if
the trigger threshold is reached, this
function provides the possibility of issuing a
warning instead of disconnecting the
equipment immediately.
The rated current of the motor circuit
breaker refers to the rated motor current
stated via parameter Rated Current 371 of
the corresponding data set.
The rated values of the frequency inverter
are to be considered accordingly when it
comes to dimensioning the application.
The function of the motor circuit breaker can be linked to different data sets. In this way, it is
possible to operate different motors via one frequency inverter. Thus, each motor can be equipped
with its own motor circuit breaker.
In case a motor is operated via the frequency inverter for which some setting values, e.g. minimum
and maximum frequency, are changed via the data set switch-over, only one motor circuit breaker
may be installed. This functionality can be differentiated by selecting the parameter Operation Mode
571 for single motor operation or multiple motor operation.
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