Testing of motor following presumed switchgear fault
Testing of motor following presumed switchgear fault
(OP)
We started a 13.2kv 7000hp horizontal sleeve bearing motor driving a centrifugal pump. As shown in flow traces, the pump ran for about 4 seconds and developed discharge pressure. At that point there was some event which resulted in something resembling an explosion in the switchgear cubicle feeding the motor (caused the switchgear to bulge), and obviouisly a motor trip.
Let's assume the cause of the fault is in the switchgear and is troubleshot and found. (not yet there, but looking ahead)
Let's further assume the motor meggers and bridges ok. (same caveat).
Would you say that any further testing is required to conclude that the event did not damage the motor?
(It occurs to me that there may have been abnormal surge voltages and also currents associated with motor feeding the fault)
Let's assume the cause of the fault is in the switchgear and is troubleshot and found. (not yet there, but looking ahead)
Let's further assume the motor meggers and bridges ok. (same caveat).
Would you say that any further testing is required to conclude that the event did not damage the motor?
(It occurs to me that there may have been abnormal surge voltages and also currents associated with motor feeding the fault)
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(2B)+(2B)' ?





RE: Testing of motor following presumed switchgear fault
Would like to see the recordings.
Gunnar Englund
www.gke.org
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100 % recycled posting: Electrons, ideas, finger-tips have been used over and over again...
RE: Testing of motor following presumed switchgear fault
RE: Testing of motor following presumed switchgear fault
I would run the motor de-coupled from the pump first, even if it is cumbersome and time consuming to do, to see and show that the motor itself is good. (after successful pre-tests mentioned earlier).
Rafiq Bulsara
http://www.srengineersct.com
RE: Testing of motor following presumed switchgear fault
Rafiq Bulsara
http://www.srengineersct.com
RE: Testing of motor following presumed switchgear fault
Properly functioning switchgear can safely carry high overloads and can safely interrupt very high currents with no damage. If your gear is properly rated and the overcurrent devices function then there is little to no chance that a fault in the motor or process caused the fault in the switchgear.
However, I agree that when something like this happens and the equipment in question is very costly then testing is called for.
Electrically you will want to test the motor for grounds or shorts. A high potential tester and a surge tester would be the appropriate devices to use. You need to apply voltages that are high enough to test the insulation and to find a fault if it exists. In most cases, the value chosen is 2E + 1kV = 26.4 + 1 = 27.4kV.
Although there is no relation to the fault, since the motor is going to be down for a while due to the switchgear repairs then it wouldn't be a bad idea to roll out the bearings for inspection if that hasn't been done in a while. If you perform the electrical tests and the bearing inspections then you can confidently say that the motor is good to go.
I am curious. Was this an across the line start using a circuit breaker or is it some form of reduced voltage starter, soft starter, or VFD?
RE: Testing of motor following presumed switchgear fault
We have no recordings of current. We use state of the art 1980's electromechanical relays. We do have some 1-second samples of voltage magnitude which tell an interesting story. The whole story is interesting and still unfolding, but there may be some commercially sensitive information (I am being intentionally vague). Maybe later more details will follow.
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