Seeing the Invisible: Partial Discharge Imaging for Large Motors and Generators - Resource Library - EASA | The Electro•Mechanical Authority
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Seeing the Invisible: Partial Discharge Imaging for Large Motors and Generators

  • July 2025
  • Number of views: 29
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Chase Fell 
Technical Education Committee Chair
Jay Industrial Repair

For service professionals working with large electric motors and generators, machines with voltage ratings 5 kV and higher can be vulnerable to invisible threats of partial discharge (PD). Corona and PD activity have long been a challenge to detect before failure occurs. Traditionally, detecting these issues required indirect methods like radio interference voltage (RIV) testing, ultrasonic detection or offline insulation tests. But recent advances in partial discharge imaging—sometimes called corona cameras—are giving engineers and technicians a powerful new tool: the ability to see electrical discharge activity directly and in real time. 

In this article, we’ll explore how partial discharge cameras work, their practical applications for motors and generators and how they can support proactive maintenance strategies in high-voltage equipment.

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