electricpete
Electrical
- May 4, 2001
- 16,774
This is a strange one.
Outdoor WP2 Vertical 13.2kv 3500 hp, 324rpm S.C.I.M driving a circulating water pump. Upper bearing in Kingsbury style in 50 gallon oil bath with cooling coil immersed in the bath.
History:
2005 - Motor rewound. Core noted to be marginal but was not restacked. Cracking performed to bring core hotspots in spec.
2009 – B phase Motor T-lead open-circuited resulting in motor trip. Bizarre failure described here.
thread237-241996
February 2010 – Partial discharge increases from approx 350 millivolts to approx 550 millivolts on B phase
3/2/2010 – motor removed for routine preventive maintenance – Megger (sat), bridge (sat), filter change (tortuous path between filters and winding by desing). Oil level was normal (high end of band).
3/11/2010 – Motor restarted. Motor was not watched carefully upon restart.
· 20 minutes after start, there was a report of blue haze coming from the bottom of the motor (this motor takes in air at the top and discharges at the bottom). Motor was manually secured 5 minutes later (did not trip).
Repeat megger test sat – 1,000 megaohms (corrected), pi > 2.
Repeat winding resistance test sat – all phases match very closely.
Inspected space heaters, inspected lower bearing area, inspected packing area. Inspected rotor, air baffle and limited view of stator through air box ports. No anomalies noted.
3/13/2010 – Restart the motor.
No smoke noted (initially). Although there was a smell that seemed to get worse.
Vibration sat.
Partial discharge still around 550 millivolts on B phase.
Thermography showed no anomalies at pump packing, motor lower bearing housing, coupling. About 12F hotter than the other motors on the motor frame.
· After about 40 minutes of running a fairly large puff of white smoke came out of the bottom of the motor lasting about 3-5 seconds and then stopped. Motor was manually secured 3-5 minutes later.
Electrical test has not yet repeated but I anticipate it is still sat (if not, then the course of action is obvious).
Discussion of temperature trend: This motor ran about 20F hotter than others before rewind in 2005, has continued 20F hotter than others. Was cleaned in April 2009 and remained hotter. Has actually increased to about 30F hotter than others over the past year. But hottest temperature last summer was 230F (hottest of 6... we check them all). And the insulation is Class F.
What say you?
1 - Practical question: Is there any logical further troubleshooting before we pull the motor and send it to the shop for disassembly / core test etc?
2 - Just for fun question. What is your prediction of likely/possible causes of puffs of smoke from a motor that does not trip and looks good on electrical testing? How likely are the following scenarios to cause this:
- Core overheating?
- Water leak into upper bearing oil reservoir causing overflow of standpipe (we haven't seen any evidence of oil but do plan to draw a bottom sample)
- Foreign material in the motor?
- Others?
=====================================
Eng-tips forums: The best place on the web for engineering discussions.
Outdoor WP2 Vertical 13.2kv 3500 hp, 324rpm S.C.I.M driving a circulating water pump. Upper bearing in Kingsbury style in 50 gallon oil bath with cooling coil immersed in the bath.
History:
2005 - Motor rewound. Core noted to be marginal but was not restacked. Cracking performed to bring core hotspots in spec.
2009 – B phase Motor T-lead open-circuited resulting in motor trip. Bizarre failure described here.
thread237-241996
February 2010 – Partial discharge increases from approx 350 millivolts to approx 550 millivolts on B phase
3/2/2010 – motor removed for routine preventive maintenance – Megger (sat), bridge (sat), filter change (tortuous path between filters and winding by desing). Oil level was normal (high end of band).
3/11/2010 – Motor restarted. Motor was not watched carefully upon restart.
· 20 minutes after start, there was a report of blue haze coming from the bottom of the motor (this motor takes in air at the top and discharges at the bottom). Motor was manually secured 5 minutes later (did not trip).
Repeat megger test sat – 1,000 megaohms (corrected), pi > 2.
Repeat winding resistance test sat – all phases match very closely.
Inspected space heaters, inspected lower bearing area, inspected packing area. Inspected rotor, air baffle and limited view of stator through air box ports. No anomalies noted.
3/13/2010 – Restart the motor.
No smoke noted (initially). Although there was a smell that seemed to get worse.
Vibration sat.
Partial discharge still around 550 millivolts on B phase.
Thermography showed no anomalies at pump packing, motor lower bearing housing, coupling. About 12F hotter than the other motors on the motor frame.
· After about 40 minutes of running a fairly large puff of white smoke came out of the bottom of the motor lasting about 3-5 seconds and then stopped. Motor was manually secured 3-5 minutes later.
Electrical test has not yet repeated but I anticipate it is still sat (if not, then the course of action is obvious).
Discussion of temperature trend: This motor ran about 20F hotter than others before rewind in 2005, has continued 20F hotter than others. Was cleaned in April 2009 and remained hotter. Has actually increased to about 30F hotter than others over the past year. But hottest temperature last summer was 230F (hottest of 6... we check them all). And the insulation is Class F.
What say you?
1 - Practical question: Is there any logical further troubleshooting before we pull the motor and send it to the shop for disassembly / core test etc?
2 - Just for fun question. What is your prediction of likely/possible causes of puffs of smoke from a motor that does not trip and looks good on electrical testing? How likely are the following scenarios to cause this:
- Core overheating?
- Water leak into upper bearing oil reservoir causing overflow of standpipe (we haven't seen any evidence of oil but do plan to draw a bottom sample)
- Foreign material in the motor?
- Others?
=====================================
Eng-tips forums: The best place on the web for engineering discussions.