Motor protection switch OH2
4.4.6.1 Asynchronous motor
Rated current of the motor protection function (in %
dr03)
Selection of self-ventilated / forced-ventilated motor
Adjustment for separate-cooled motor
Adjustment for self-cooled motor
The motor protection function protects the connected motor against thermal de-
struction caused through high currents.
The function corresponds essentially to the mechanical motor protection compo-
nents, whereby the influence of the motor speed to the cooling of the motor is addi-
tionally considered.
The load of the motor is calculated from the measured apparent current (ru10) and
the adjusted motor protection rated current In (dr34motorprotection curr. %).
The following tripping times are valid for a separate cooled motor or at rated frequency of a
self-cooled motor:
The tripping time decreases for self-cooled motors with the frequency of the motor.
The motor protection function works integrating, i.e. times with overload of the mo-
tor are added, times with underload are subtracted.
After triggering of the motor protection function the new triggering time reduces,
unless the motor was not operated for corresponding time with underload.
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