Possible causes for over braking faults, OBF, on the ATV61 or ATV71 drives
DC Bus voltage reaches trip threshold
The VFD monitors the voltage on the DC Bus. If it reaches the voltage trip threshold while the VFD is in running status, the VFD faults OBF. There are multiple causes to a high DC Bus voltage.
If the drive trips at starting:
- Check that the Catch on the Fly parameter is enabled in the Fault Management menu (if application allows)
- Review the power circuit for sources of a power disturbance. These are typically poor electrical connections at breaker/contactor contacts, wire terminations, fuse clips.
- Consider arcing within windings of a transformer, line/load reactor, and motor.
- Measure line voltage on the drive L1,L2,L3 terminals (phase to phase) and check for any high voltage.
- Check mains voltage reading in the 1.2 Monitoring menu to see what the drive is seeing coming in.
- Measure DC bus voltage to see if it's too high. Should be approximately 1.41 times the line voltage.
- Consider adjusting acceleration time up or down.
If the drive trips during normal running speeds:
- Monitor for voltage surges and spikes
- Consider adding a line reactor or surge suppressor
If the drive trips while decelerating:
- Increase the deceleration time
- Regen from an overhauling or high inertia load will increase bus voltage
- Consider adding a Dynamic Braking resistor
For ATV71 applications with off center loads (Jack pump, shaker table, vibratory feeder) it would be worthwhile testing the ENA System set to YES (Menu 1.4 [Motor Control]). Note that the Motor control type must be set to SVC V.