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TOSHIBA
0
Time
0
Time
(a) During operation
Figure 15 Stator
temperature rise
In other words, the stator temperature rises exponentially during motor operation
to a certain temperature that is determined by the current magnitude.
When the
motor is stopped, the stator temperature falls down to the ambient temperature.
This relay determines whether the motor is running or at rest by checking the
Then it performs the calculation of equation (1)
presence of the stator current.
or (2) to simulate the heated condition of the motor.
The stator current is samlped at predetermined intervals and the sampled currents
are successively fed to the calculation process in order to perform the thermal
simulation in response to the changes in the motor operating condition.
Figure 16 shows a timechart that represents changes in the simulated temperature
rise in response to changes in the motor operating condition (current changes).
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