Aaaaaaaand it's back. So back in November when this initially happened,I contacted ABB for help. The dude sent me a sheet on how to test the thyristors inside the unit. So I did what it said, I disconnected all the wires attached to the outside, took the cover off, disconnected all the wires inside, did some ohm checks, all seemed to check out ok. Put the thing back together, and it worked perfectly like it should. Ran fine for 5 months, now it's acting up again.
Same issue occured, fan tripped and it's now down. Same set up however, it was time to swap the fan motor so the old one can be serviced/rewound. Got a new motor in it, transformer has been fully tested by outside shop with a clean bill of health, not shorts,etc. Also got a brand new identical ABB softstarter in it. I copied the settings from old unit and entered it into the new one. First test, smooth start up, all is well, as were subsequent manual starts. Put it in for production run and it craps out.
Things I've observed. With motor disconnected and only the transformer on the load side, it makes some gnarly noises, the voltage output on softstart is erratic. Not a smooth 20 sec progression like it's set. Transformer (no load attached) was pulling erratic current, spiking as high as 60A and back to 0 and everything in between. With motor attached, (100hp 230V) I watched the amps spike to 420A as soon as it started and worked it's way down, then slowly up to tripping point of breaker attached inline with motor. I was convinced it was something to do with the xformer, even though all the experts told me otherwise.We pulled wires off of the transformer, hooked up a portable 480V fan to the softstarter, fired it up, ramped up nice and smooth, amps were like 1.5A, voltage ramped up like it was supposed to. I was certain at that point it was the transformer. Took out the portable fan, came back the next day to check some more stuff. Nothing hooked to softstarter, no control calling for action, the output is sitting at 480V. Display screen shows 0% output, removing the fuse for 120VAC control power to the softstarter so it powers down, and it's still outputting 480. Pulling disconnect, and powering back on, still 480V. Pretty sure we have a shorted thyristor now. No longer do I think it's the transformer down stream. Now I need to look upstream, any suggestions? I've checked control voltage to unit which was odd that my meter hesitates when checking high voltage and does a beep first. It did it on the 120V, showed something like 500 volts then immediately down to 88, then 122. PLC commands the softstart as well as a HOA switch on panel. There's a purple and an orange wire on the softstart I assume one provides steady voltage and the orange connects to the start and stop terminals to control. Traced the purple and orange to an ice cube relay that I assume comes from PLC to make the connection. During earlier tests, removing that relay didn't break the 480 output either. I read around a little and it sounds like a no voltage scenario wouldn't necessarily stop the SCRs from conducting, it would actually take a voltage signal to make it stop. I don't know much about this, but unfortunately nobody else does either and we are dead in the water here, so any recommendation on places to check for faults. The softstarter appears like everythings cool, no fault code or protection light. I checked voltage between the orange and purple and didn't get any voltage. But, that was after the stuck on condition. Could there be a problem on the internal power source? Just need to find the root cause of that. Sorry for lengthy post, just wanted to fill in all the details I could remember.