We experienced the simultaneous failures of two 4kV fan motors on a high resistance grounded system. They were on the same switchgear bus, a 6000 HP fan (located outside) and a 600 HP fan (inside) – both less than 300 feet from the bus. The 6000 HP fan has surge protection at its terminals – the only other surge protection is on high side of main transformer. Our control system shows the loss of the 6000 HP fan one second before the 600 HP fan, however, the points have a 0.5 second scan time and it is too close to call if that is real or not. The 6000 HP fan went on instantaneous at 8920 A (740 FLA) and one end coil was visibly blown out, and the 600 HP fan on time overcurrent at 1160 A (76 FLA). No abnormal weather or operating conditions. A similar situation occurred previously wherer we got a 2-fer in failures. Any ideas?
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Simultaneous 4kV Motor Failures 2
- Thread starter joepower
- Start date
electricpete
Electrical
Correction
D=outer diameter, d = inner diameter, both in inches.
D=outer diameter, d = inner diameter, both in inches.
electricpete
Electrical
More values of SIC
PVC: 3.5-8.0
EP - 2.8-3.5 (that is what I reported above).
Polyethelene - 2.3
XLPE - 2.3-6.0
PVC: 3.5-8.0
EP - 2.8-3.5 (that is what I reported above).
Polyethelene - 2.3
XLPE - 2.3-6.0
- Thread starter
- #43
- Thread starter
- #44
A picture of the failed 6000 HP motor is at:
A diagram of the surge suppression setup is at:
Both the metal-oxide surge arresters and capacitors are rated for use on a high resistance groudned system. Capacitors are 0.5 microfarads per pole.
A diagram of the surge suppression setup is at:
Both the metal-oxide surge arresters and capacitors are rated for use on a high resistance groudned system. Capacitors are 0.5 microfarads per pole.
electricpete
Electrical
Can you tell us a little better what we're looking at?
Can we see bare copper? Evidence of melting => turn-to-turn fault?
Was it found this way or pulled apart for inspection?
Is this the connection end. I think I can see jumpers attached on the outer edge just out of view, but not sure. Does it look like perhaps the fault started at the point where the jumper enters the knuckle? That "scarf joint" in taping is a natural weak point.
Or does it look like it started closer to the slot where there might have been ground fault. I'm guessing not.
One more question, surely not related to the failure: are those rub marks that we see on the stator bore? Surely not since the pattern is so regular. What is it?
Can we see bare copper? Evidence of melting => turn-to-turn fault?
Was it found this way or pulled apart for inspection?
Is this the connection end. I think I can see jumpers attached on the outer edge just out of view, but not sure. Does it look like perhaps the fault started at the point where the jumper enters the knuckle? That "scarf joint" in taping is a natural weak point.
Or does it look like it started closer to the slot where there might have been ground fault. I'm guessing not.
One more question, surely not related to the failure: are those rub marks that we see on the stator bore? Surely not since the pattern is so regular. What is it?
electricpete
Electrical
Conductors blown apart make me think of currents flowing in opposite directions. One scenario is turn to turn fault. Current induced in the shorted turn is opposite direction from other turn currents and can be very high magnitude.
Gentlemen (oops, and ladies if present):
When you discuss continuity of production or "production safe" you are, of course, using the same convoluted logic used in ungrounded LV systems. Additionally, even though you are generalizing, hopefully you are limiting such systems to "unclassified area" installations!
When you discuss continuity of production or "production safe" you are, of course, using the same convoluted logic used in ungrounded LV systems. Additionally, even though you are generalizing, hopefully you are limiting such systems to "unclassified area" installations!
jbartos
Electrical
- Jan 15, 2000
- 6,440
- 0
- 0
Suggestion to the first link showing the motor winding damage. It appears to be a turn-to-turn short as stated in the above electricpete posting; however, the root cause analysis may or may not be very conclusive for one cause because of the surge protection, age of motor winding, power supply quality, etc. factors.
- Thread starter
- #49
The multiple electrical failures in the 6000 HP motor were generally "in the slot", or phase to ground rather than phase to phase. The rub marks seen in the photo are interpreted by the rewind shop to be wear marks from an abrasive dust environment, although I still need some convinving. Both motors did have heavy crud buildup which probably didn't help their temperature any. And for those fans of "almost in time" maintenance, the 6000 HP was scheduled to be sent out for refurbishment 4 days after the failure. The probability is high that I have a set of 30-year old motors that have seen some hard times and are at the end of their insulation life and some relatively minor item could trigger the failure.
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