Figure. 5.4.23 - 119. Matching thermal replicas to the measured thermal capacity of the motor.
As can be seen in the figures above, when the motor is loaded with a constant current both of the
replicas (single and dual time constant) follow the motor heating quite accurately. The operational
difference is during cooling. With a single cooling time constant the replica does not follow the actual
cooling of the motor and the match can be said to be very poor. With dynamically-controlled cooling
time constants the match is very accurate. If this motor were used for cyclic loads with repeating
cooling times, the single time constant model would stretch into the next duty cycle and probably
cause unnecessary alarms or even trips eventhough the motor were till running in safe temperatures.
Thermal trip curves
Motor thermal curves are useful when studying motor heating in possible overload and start-up
situations. These are usually available upon request from manufacturers, and the relay operation can
be set according to these.
A
AQ
Q-M257
-M257
Instruction manual
Version: 2.07
© Arcteq Relays Ltd
IM00021
235
Summary of Contents for AQ-M257
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