BEARING/COMMON MODE current in PWM fed induction motors

[eldhobaby]

I would like to know about the common mode currents that flow through the bearings of PWM inverter drive fed induction motors.These cause destruction to the bearings.

It would be very nice if i could get details about the shape of these waveforms.

Thank you in advance:)

[marke]

Hello eldhobaby

 

There are a number of papers on this subject and an internet search will show some of them.

Essentially, the output of an inverter is a pulse width modulated waveform with the output switching between the +ve and -ve rails of the DC supply.

With IGBT switching devices, the voltage switches very quickly. These rapid switching edges of the output waveform are capacitively coupled to the rotor. The current flowing in the bearings is a series of very short current pulses. The width and amplitude of these pulses is dependent on the switching time of the output devices and the frequency is dependent on the carrrier frequency of the drive.

The currents can be reduced by fitting of a dv/dt filter on the output of the drive.

 

Best regards,

[ABBdrives]

Hello eldhobaby

 

There are a number of papers on this subject and an internet search will show some of them.

Essentially, the output of an inverter is a pulse width modulated waveform with the output switching between the +ve and -ve rails of the DC supply.

With IGBT switching devices, the voltage switches very quickly. These rapid switching edges of the output waveform are capacitively coupled to the rotor. The current flowing in the bearings is a series of very short current pulses. The width and amplitude of these pulses is dependent on the switching time of the output devices and the frequency is dependent on the carrrier frequency of the drive.

The currents can be reduced by fitting of a dv/dt filter on the output of the drive.

 

Best regards,

 

 

A common mode filter is a very good alternative also ensure proper grounding at the drive and motor end to return the high frequency current to the drive.