TOSHIBA
6F9EOlll
0
Time
0
Time
(a) During operation
(b)
At reset
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
presence of the
stator
current.
Then it performs the calculation of equation (1)
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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