Expert: Aaron Overbeek - 3/5/2009

Question
what are the factors causing the motor to get burn if it is connected to frequency inverter. The distance of the motor is about 50meters away from the frequency inverter. The motor is 6leads out, 460V, insulation F, Class B but it was already rewinded for 3 times. does this factor greaty contribute to motor windings burn out?

Answer
The windings of a motor are wrapped closely and kept separated only by a thin layer of insulating lacquer

This lacquer can deteriorate by
a) age
b) weather changes
c) heat (due to current flow)

Generally the insulation lasts a lifetime but can lose its properties faster if
a) there is dirt and dust - especially where there are oily fumes like in kitchens
b) there are water droplets - such as in shower room exhaust fans

Thirdly a motor winding can burn out by overload (excess current)
a) if the rotation of the fan is mechanically blocked (some object preventing it from turning)
b) if the AC capacitor is defective - preventing rotation
c) if the bearings are seized (stuck)