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CHAPTER 3: MOTOR PR OTECTION
3.1.4 Cooling rate
The thermal cooling model causes the accumulated motor heating value to decrease exponentially when the steady-
state accumulated motor heating value is less than the actual accumulated motor heating value. The cooling time
constant (K) is programmable up to 15 times the time constant for the selected trip class. Figure 3-2 through Figure 3-
9 show the thermal cooling model following a trip at time equal to 0, using trip class 5 through 40 and a K from 1 to
15.
When the accumulated motor heating value reaches 68%, the motor is considered to be in a cold operating state and
the cooling stops.
The cool down factor can be set in the WinESG parameterization/device settings panel shown in the illustration
below, or Modbus function code 6 register 12.
Example:
If the EntelliPro ES unit is set to class 5 and cool down factor to 1, it will take approximately 59 seconds after a trip for
the motor to cool. If the cool down factor is set to 15, it will take approximately 889 seconds for the motor to cool and
the reset to be allowed.
After an overload trip, the time to restart is available on WinESG measure panel shown in the illustration below, or
Modbus function code 4 register 64 or Profibus class 1 telegram B2704.
The accuracy is ±10%.
NOTE:
Reset is not allowed until the motor is considered in cold state. Before restarting, the motor should be allowed
to reach a cold state.
Figures 3-3 to 3-10 show the different cooling curves rate for each IEC trip time class.
Refer to NEMA Standard MG10 for information regarding the required cool down time between successive starts.
3.6
EP OS MOTOR MANAGEMENT SYSTEM – INSTRUCTION MANUAL
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