VFD Induced Shaft Voltage Testing

Variable-Frequency Drives (VFD) used to control the speed of motors are known to require significantly less energy than traditional drive units. Because of their energy savings potential, variable frequency drives are being installed on all types of equipment including heating, air conditioning, ventilation, and refrigeration systems as well as pumps, blowers, ID Fans, FD Fans, etc.

Electric currents and voltages generated by VFDs can cause significant damage to motor bearings or other coupled equipment components if connected by couplings with conductive components.

Electric currents caused by shaft voltage can cause electrical pitting damage (EDM) and lubricant degradation of the motor bearings. 

It is essential that motors being operated by VFDs be tested to see if there are harmful shaft voltages present and if so that the motors be retrofitted with Shaft Grounding Rings (SGRs) and/or ceramic or insulted bearings or other alternate discharge grounding methods to mitigate the harmful voltages.

MTI’s shaft voltage testing capabilities will analyze the voltage levels to determine if mitigation efforts are required. If harmful voltages are found, MTI’s test equipment can also be used to determine if  and if a SGR will be a sufficent solution to mitigating the problem.

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