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Vacon variable frequency drive problem

As maintenance engineer in a sugar factory, I have been having problem with induction motor 37Kw driven by variable frequency drive (VFD), type Vacon NXS, this motor is running normally at 1200 rpm with draw current about 8.5A, the thing is that this motor was stopped working the drive HMI shown "Saturation Trip" which was indicating the drive is gone, we changed the drive & fuses with a new one and the motor restarted.

The same problem happened yesterday for the same other motor 37Kw, I found the VFD main breaker was tripped and there is abnormal sound internal the drive, I turned it ON for control supply to what is HMI showing to locate the fault and keep the VFD drive ready for start, then the drive’s HMI was ceased to function and did not shown the parameter, after checking I found the 3-Φ fuses 63A was blown, motor & power cable meggering was in GΩ .

The question is:
• Why the fuses was blown while this motor is running normally?
• why the variable frequency drive component defective when the fuses blown? while there is no over-current or short-circuit coming through the motor or power cable.
• What is the “Saturation Trip” cause to the VFD?

1) In case you are using vacon 690VAC VFDs, you should have an output du/dt filter to protect the motor from voltage stress. This is true for all VFDs.
2) The first vfd has tripped on Saturation Fault which indicates that there could be a component defect in the drive. For the second case, fuses are blown which could indicate blown input rectifier bridge or short in DC Bus due to IGBT failure.
3) In the second failure, you mention that you heard a noise and the Main Breaker tripped. Main breaker has tripped due to high current. You should always check power components before turning on mains supply if the main breaker has tripped.
4) As you have had two failures in quick succession, I would recommend that you have a look at the input voltage also.

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