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ATV61EX**** drive trips with "Internal thermal sensor fault - THSC" as soon as run command is given to the VFD? How to solve the problem?

The fault happens due to the defective temperature sensor - installed in heat sink of the drive. The temperature sensor can be defective either by short circuit or open circuit. The fault message will be displayed in drive as below.
INFB : Internal Thermal Sensor Fault
You should check whether the temperature sensor is installed properly or not in drive. If you measure the resistance with multimeter in temperature sensor's connector (X24 & X58), the resistance of the temperature sensor should be 5kΩ on 25°C.

You can also monitor the drive thermal state in drive monitoring menu and the same should linearly increase according to the drive's temperature. If the thermal state is 0 or the value is not changing according to raise in temperature, you may replace the temperature sensor. The thermal sensor fault can also happen due to control board and power board failure, hence If the problem is not solved after changing the thermal sensor, it is recomended to replace the gate driver board and control board.