5KV Synchronous Motor trip

[adityalagudu]

We have 4160V, 500HP Synchronous motor tripped yesterday. There are no flags on the GE multiline relay and the PF trip is disabled on the relay. We did the Megger, Temp measurement, PI on the motor, everything is normal. This Motor is 25 years old, and the excitation is not AVR controlled, it is through a Rheostat. There is no fluctuation observed on the upstream. There is no overvoltage or under voltage when the trip happened. What could be the other things that need to be looked into on the synchronous motor trip?

 

[waross]

Take a look at any field wiring to any remote stops or interlocks.
Inspect the contacts in any devices in the stop circuit.

There is no overvoltage or under voltage when the trip happened.

Are you sure?
Too many times we hear something like this, followed by indignation when we query it, only to be followed eventually by the admission that the original suggestion was, indeed, the cause of the issue.

Bill
--------------------
"Why not the best?"
Jimmy Carter

 

[electricpete]

I would get out the control circuit and look at everything that can trip the breaker.
If you post it here some people may have ideas.
For our pumps there are often things like pressure switches or level switches that can trip the breaker.
Often open / intermittent circuits within the contorl circuit can trip the breaker.
We like to troubleshoot right after the trip by checking voltages at various points in the control circuit to narrow down what went open. Once you start manipulating switches and such you may lose evidence.

EDIT - I see Bill beat me to it. He's a troubleshooting warrior, you can't go wrong listening to him.

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(2B)+(2B)' ?

 

[oldfieldguy]

What Bill and Pete said.

We had a 5 kV compressor motor that tripped randomly without flagging either the electrical or process control protection for YEARS. The motor, the compressor, the monitoring equipment, the protective relay, all were tested multiple times.

Only when we were doing a control upgrade did we find a terminal screw that was just a tiny bit loose, opening the voltage feed to the control circuit, allowing the contactor to drop out randomly. A quarter turn on that screw to tighten it fixed years of pain.

Go through the circuit looking for things like this. You've already eliminated the big, fun, active things, so it can be something simple, but just wrong.

old field guy

 

[jraef]

On a similar vein, I had an 800HP compressor that kept shutting down with no indication of the cause. It was on a Soft Starter but the starter showed no faults, no trips, nothing out of the ordinary. I got called out after multiple people had been checking all kinds of things. I was frustrated too, but actually got to WITNESS it shutting down, it was happening on start-up, not while it was actually running. So I looked at the control circuit and found the Run command to the Soft Starter was coming from a board on the compressor. After downloading the manual and calling the manufacturer, I found out it had an incomplete sequence timer built into it, based on it being expected to control a Y-Delta or Autotransformer starter. So if the compressor was not at a set pressure within 2 seconds, the controller assumed the starter had failed to transition and shut down. But of course there was no 2 step electromechanical starter, so sometimes if the line voltage was a little low and the Soft Starter took longer to accelerate the motor, the compressor board misinterpreted that and shut it down. I disabled that feature in the compressor board and never had another problem.


" We are all here on earth to help others; what on earth the others are here for I don't know." -- W. H. Auden

 

[RRaghunath]

If there is no known reason for trip, then, it is time to look at the DC system earth fault alarms.
Possibly, there is an uncleared earthfault, that played mischief on occurrence of second fault at a wrong location.
Often, I have seen people taking DC system earth fault alarms lightly (in a high resistance/ unearthed DC systems).