Chris

I also think the fault is in the inverter and most likely in the power transistor block that generates the 3 phase output from the DC link. The inverter would have initially caught the over current condition as a transistor went short circuit and later the blown transistor would produce an open circuit fault.

CS

I would agree it is likely the inverter has failed – but it could also be the motor, too.

I would be checking the resistance of each phase, not just continuity. If one phase is internally shorted …..

Edited By not done it yet on 30/03/2023 19:50:38

I agree, new VFD.

A possibility not mentioned is the fault was caused by a cable or connector fault. If one of the connections between a 3-phase motor and VFD breaks, maybe due to a screw-terminal vibrating loose, or a cable getting metal fatigue, then the unhooked winding is liable to generate a spray of high-voltage pulses which can damage the VFD. (Thousands of volts – the winding behaves like a car-ignition coil rather than turning the rotor.)

Worth double-checking the connections and wiring. When a multicore cable fails, it usually goes intermittent rather than failing in plain sight. A straight resistance test may not find the problem; it's necessary to apply an analogue meter and watch the needle as the cable is flexed. The fault is more likely to be near an end than in the middle, but it depends on the installation. Breaks usually occur where the cable can move or rub going through a bulkhead, not in inside runs firmly fixed to the machine.

Soldering multicore to terminators is a common cause of fatigue failures because the solder wicks down the wires and creates a stress-raiser. If soldered, make sure the cable is OK near the joint.

Most likely the VFD failed due to age, but there's a chance the wiring was iffy.

Dave

I had a dead Altivar VFD , The fault was in the power output block. Surprisingly, I googled the output block number and found several sellers in China. Cost around £8 and the Altivar was fixed.

Andrew.

Been there, done that. Although, in my case the motor was very lumpy. Given that the VFD was built into the lathe cabinet, it was easier to change the motor, but no luck there.

So a new modern VFD was fitted. It solved the problem for a while, but then exactly the same problem recurred.

Fortunately, a replacement under warranty was fine and has continued to work for a few years now.

Really and truly, there isn't much (if anything at all) to go wrong with a 3-phase motor so the learning point was to fix the VFD first.