Flow Ctrl Tech Engineering

Debugging VFD Trips: Ground Faults, DC Bus Overvoltage & Regenerative Braking

Field diagnostic procedures for variable frequency drive faults: using a 1000V Megohmmeter to test motor insulation, calculating dynamic braking resistors, and diagnosing decel overvoltage.

  • Rapidly decelerating a high-inertia load turns the AC motor into a generator, dumping energy onto the DC bus.
  • If regenerative energy exceeds capacitor absorption limits, the drive trips on Overvoltage (OV).
  • NEVER apply a 1000V Megohmmeter to motor leads while still connected to the VFD; disconnect motor leads first to protect IGBTs.

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