S****** GM-150 VFD

[oldfieldguy]

We have three, two 9000 horsepower, one 7000 horsepower. the 7000 went in service three years ago. It has had two failures, each requiring three weeks outage between bringing in the expertise to diagnose and then to get parts to repair major damage to bus.

One of my 9000 horsepower units is presently down from its SECOND major fault. We've been out a week. An entire rack of IGBT modules blew out this time, major bus damage, and yesterday we discovered damage to an output reactor, apparently due to current load causing physical movement between the coil and core. The motor and cables tested okay.

Our running conditions are well within equipment rating for voltage and current. We don't even have a cyclic load, just running centrifugal compressors for days on end.

Three units. Three years. FOUR major failures. Never the same problem twice. Understandably, the manufacturer is not giving us the history of other failures on the installed base. Therefore I am putting it out on the list.

Is there anybody else out there with these things? What's YOUR experience?

Excuse me while I go in the corner and sob quietly.

old field guy

 

[Skogsgurra]

Have had a similar thing but that was on a 690 V grid - which I do not think you have(3 or 6 kV?). Several inverters just blew up. Repedtedly. Smoke stack fan, primary air fan and such stuff.

We finally found that the PF compensation capacitors were switching (unnecessary to have PFC in the first place) much too often. We killed the automatic PF controller and never had a problem since.

We never got so far that we actually measured voltage from motor to ground. We saw nothing between motor phases. But we think that there could have been transients to ground. The reason for this is that we could identify destroyed varistors that were connected from inverter output to ground and it seems that these were the ones that started it.

Gunnar Englund

http://www.gke.org

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