MV Motor damage but VCB not trip 1

[Jed057]

any guru,

I am facing the problem that

MV (6.6 kV) motor (1250 kVA) of compressor broken but VCB didn't trip.
The VCB was opened by operator when they hear big noise and vibration.


our Setting is

Motor start time = 9 s

Lock rotor relay;
= 300% In
t= 9s

50 Relay;
I=8.5 In
t=15 ms

49 TOL;
I=250
t=1.3 s

Unbalance relay

How about setting of 51LR lock rotor relay (REF 542+)?
Is it too lond time for 9s?
What is normal practic for 51LR setting?
Why VCB didn't trip before motor damaged ?


Thanks for your answer

young eng.

 

[electricpete]

Did the noise occur upon start? How long after start? Was the machine observed to rotate during start?

What was found upon investigation after shutting the machine down?

Any electrical problems. megger test results sat? winding resistance equal? Visual inspection of end turns?

Mechanical checks: machine rotates smoothly by hand? What type of bearings?

What is it that you meant by "motor damage"?

We don’t really know enough to have a clue yet but it is certainly possible you have a mechanical problem that did not yet progress to an electrical problem. The machine may have come up to speed drawing normal current but just making a lot of noise.

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[Zogzog]

Did you have any "targets" on any relays?

 

[PQ101]

JED057- please elaborate more on sequence of events leading to damage, attach pictures. etc. and explain in detail what was the damage i.e. mechanical-bearing failure, or motor winding short-failure. Has the motor been checked for forensics?

Assuming all the settings are correct: If compressor motor experienced overheat(overload)Device 49 should have picked up to protectct. If single-phasing was the issue, unbalnce relay would pickup. Main breaker would pickup on instantanious or short circuit fault. But, none of them did. I'm wondering if this motor had experienced any other issues in the past!!!was it equipped with phase-winding RTD's for motor protection? how is the quaility of incoming service? was there winding failure on one phase or all 3-phase.



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[Zogzog]

I think the first thing to figure out is , did the breaker not trip when a relay told it to or not. Either a breaker issue or a relay issue.

 

[electricpete]

I had already ASSumed no relay trip, otherwise why would he be asking about relay settings?
Guess we’ll all have to wait and let him figure out what’s the first thing to figure out ;-)


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[TurbineGen]

I'd start looking into the relay operation and the connections first. Did you test the relay to verify that it operates properly? Did you test the relay connection to the breaker to verify it in fact trips the machine? I can think of several instances where somebody forgot to reconnect the trip command after testing a relay.

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If it is broken, fix it. If it isn't broken, I'll soon fix that.

 

[edison123]

What exactly was 'broken' in the motor ?

Muthu

http://www.edison.co.in

 

[PHovnanian]

What exactly was 'broken' in the motor?

It could very well be the driven load as well and the motor is just fine. That's pretty typical behavior in my workshop :-(

 

[rbulsara]

Over current is not the only reason or effect when a motor fails. Motor can fail due to mechanical reasons too.

These type of events can only be correctly analyzed by having someone experienced/knowledgeable on site.



Rafiq Bulsara

http://www.srengineersct.com

 

[oldfieldguy]

"MV (6.6 kV) motor (1250 kVA) of compressor broken but VCB didn't trip.
The VCB was opened by operator when they hear big noise and vibration."

It may NOT be the motor at all. I've made a lot of good money over the years determining that the motor and breaker were okay but there were problems with the mechanical stuff people insist on hanging off the end of the motor shaft.

If possible, disconnect the motor and turn the shaft by hand. It should be possible with this size motor. That will give you some idea about loud noise and vibration. If the motor turns freely, you might want to get your mechanical folks to check your mechanical load.

If the shaft will turn by hand, then do some simple electrical tests on the motor to eliminate possible insulation failures.

If you've had previous correct operation of the protective relays, you might want to do a start with the motor uncoupled. If you suspect incorrect operation of the protection and controls, this is a good time to test these things thoroughly, then test run.

old field guy

 

[PHovnanian]

It may NOT be the motor at all. I've made a lot of good money over the years determining that the motor and breaker were okay but there were problems with the mechanical stuff people insist on hanging off the end of the motor shaft.

If we could just stop people from connecting mechanical stuff to our motors, they'd all run just fine. ;-)

 

[oldfieldguy]

PHovnanian--

That's pretty much my take on the situation, but I'd be just as happy if they'd just be able to have an equipment failure where I don't have to out there and prove beyond a shadow of a doubt that it's NOT electrical.

Case in point: Production supervisor calls me. His blower is tripping off on overload. It had previously been in service twenty years with no problems. Now it's tripping on overload.

My first question: Has there been any work done on the blower recently. His answer: Yes, just came back from rework.

I told him that motors don't suddenly develop a 25% overload and that he needed to make sure the shop hadn't installed a larger impeller. The names and insinuations I received for suggesting such a thing weren't nice.

I did the complete battery of tests: Insulation, winding resistance, test runs for current balance and voltage problems, monitored real and reactive power. Everything pointed to a normal motor with a bit too much mechanical load. I wrote up the report and let them have it. No motor problem.

A month or so later I asked one of the mechanical people about the blower. "You didn't hear? " he said? "The shop put the wrong impeller in it when they rebuilt it. They took it back and fixed it."

And the guy who was happy to tell me **I** needed to stick with electrical stuff and let HIM take care of the process equipment has yet to tell me that he was wrong.

So to the original poster of this thread, take heed. You need to look at the whole system.

old field guy

 

[racobb]

Pretty hard to beat a man at his own game, huh! When you are wrong they are always quick to let you know, but when you are ocassionally right, you don't hear anything.

Alan