Chuck Yung
EASA Senior Technical Support Specialist

Concerns about partial discharge (PD) used to be limited to repairers and users of machines rated over 7 kV – and PD was a common consideration for machines rated 11 kV and higher. Since the advent of variable frequency drives (VFDs), PD activity is a major contributing cause to winding failures in 460v and (especially) 575v motors. This paper will describe PD, explain how to detect it, and offer repair solutions.

Topics covered include:

• Explanation of partial discharge (PD)
• Description of damage mechanism
• PWM drive and PD
• How to evaluate PD
• Repair tips

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