By drive model
By symptom
Why a variable-frequency drive trips while ramping up, usually on overcurrent, and how to separate ramp settings, mechanical load and motor or cable faults.
SymptomVFD overvoltage during decelerationWhy a drive trips on DC bus overvoltage while slowing down, and how deceleration time, the overvoltage controller and braking resistors affect it.
Overview
Variable-frequency drives run the pumps, fans, conveyors and compressors in almost every plant. Different manufacturers number their faults differently, but most trips fall into a handful of families: overcurrent, DC bus over- or undervoltage, ground fault, overtemperature and communication loss.
Common problems
Overcurrent trips
The drive saw more current than its limit. Typical causes are acceleration ramps that are too short for the load, a mechanical jam or brake that is not releasing, or a motor or cable insulation problem.
DC bus overvoltage
Usually regenerative energy during fast deceleration of a high-inertia load. Check the deceleration time, whether a braking resistor or chopper is fitted and working, and the incoming supply voltage.
DC bus undervoltage
The supply dipped or a phase was lost. Compare the trip times with supply events, and check fuses, contactors and terminal tightness on the input side.
Ground (earth) fault
Current is leaking to earth in the motor, cable or drive output. Insulation testing must be done with the motor disconnected from the drive, following the manufacturer’s procedure.
Drive overtemperature
The heatsink or internal temperature exceeded its limit. Look at cooling-fan operation, filter and heatsink cleanliness, cabinet ventilation and ambient temperature.
Evidence that helps
- Photo of the keypad fault display
- Drive make, model and rating from the nameplate
- Fault log or parameter export
- What the driven machine was doing at the time