Drive control and features
45
Thermal motor protection model
The drive calculates the temperature of the motor on the basis of the following
assumptions:
1) When power is applied to the drive for the first time, the motor is at ambient
temperature (defined by parameter 45.05 AMBIENT TEMP). After this, when power
is applied to the drive, the motor is assumed to be at the estimated temperature
(value of 1.18 MOTOR TEMP EST, saved at power switch-off).
2) Motor temperature is calculated using the user-adjustable motor thermal time and
motor load curve. The load curve should be adjusted in case the ambient
temperature exceeds 30 °C.
It is possible to adjust the motor temperature supervision limits and select how the
drive reacts when overtemperature is detected.
Note: The motor thermal model can be used when only one motor is connected to
the inverter.
Temperature sensors
It is possible to detect motor overtemperature by connecting a motor temperature
sensor to thermistor input TH of the drive or to optional encoder interface module
FEN-xx.
The resistance of the sensor increases as the motor temperature rises over the
sensor reference temperature T
ref
, as does the voltage over the resistor.
The figure below shows typical PTC sensor resistance values as a function of the
motor operating temperature.
100
550
1330
4000
Ohm
T
Temperature PTC resistance
Normal 0…1 kohm
Excessive >
4 kohm*
*The limit for overtemperature
protection is 2.5 kohm.
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