Invertor or Motor Problem?

My lathe is powered by a 1.5kW 3 ph Tec motor driven by a Telemecanique Altivar 28 inverter off a single phase supply. Today, machining happily away, stopped the lathe to check a diameter dimension, on restarting there was a loud pop from the direction of the inverter and nothing else happened. Lathe immobile. The inverter displayed a fault code that said the fault was over current. Reset and tried again, same result. Thinking there was a blockage stopping the motor turning over, turned the chuck by hand, turned over easily, so reset the inverter and tried again. This time the fault code said the fault was an open phase.

So, checked all connections, all tight. Motor obviously connected in delta and tested all winding connections for continunity, all good and no leakage to earth. Disconnected motor cables at inverter, tested each one for continunity between inverter and motor, all good. Tried starting the inverter with motor cables disconnected and same fault code displayed - open phase.

Now I am no electrician and don't know where to go next - hence this post!

To me, rightly or wrongly, I think the motor and cables are OK and I have a fault in the inverter but I am happy to be corrected. If so, its a new inverter I guess, a repair would not be economic I would imagine. If not it has to be the motor, and same logic I guess applies.

Anyone able to offer an opinion on this please?

Chris

Edited By ChrisH on 30/03/2023 18:34:46

Edited By ChrisH on 30/03/2023 18:43:47

Almost certainly the inverter. I had one of that make that failed though a different fault, the basic cost of getting it looked at was more than a new unit.

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 agree that it is most likrly to be an inverter fault. You could eliminate the motor by connecting 3 old fashioned incondescent lamps between the thee phase output of the inverter. (NOT LED OR CFL LAMPS.)

Les.

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

Just check for equal phase to phase resistances.

Will check tomorrow the phase resistences as suggested before ordering a new inverter.

Think Clive's explanation has merit as to what happened.

Thank you all for your input and confirmationary thoughts - much appreciated.

Chris

Edited By ChrisH on 30/03/2023 22:18:58

Just to complete - tested all motor phases for resistence, all equal, no shorting across to another phase or to earth,

Will bite the bullet and order a new inverter - ouch!

Chris

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

Just a thought when checking for motor faults.

Checking resistance values on a motor are no guarantee to find a short circuit. A short between adjacent turns will produce resistance values very similar to the overall resistance figure but a shorted turn will draw huge current when its energised.

If the fault is across a large part of the winding then it may show up by measuring resistance.

Martin

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.

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.

Double post.

Edited By Andrew Tinsley on 31/03/2023 18:16:18

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.