Burned out new 340 hp motor
Burned out new 340 hp motor
(OP)
Installed a newly rewound 340hp motor on our air cond. chiller unit about a month ago. Ran chiller for about two weeks. Encounter no problems. Today, I switched on the chiller and after about 4 min. of running, the motor burnt out.
Question: The chiller is designed with a solid state starter. Could the starter be the cause of the burn out? I don't want have the motor rewound and have it burn out again.
Question: The chiller is designed with a solid state starter. Could the starter be the cause of the burn out? I don't want have the motor rewound and have it burn out again.





RE: Burned out new 340 hp motor
Seems to me you need some serious protection installed.
Single phasing is a common killer of refrigeration motors.
It can also be caused by faulty overload safeties, loose connections, bad contacts, faulty semiconductors in a soft starter. Could also be a bad rewind. Water.
Why did you have to replace the motor the first time?
Others will have further ideas.
Keith Cress
Flamin Systems, Inc.- <http://www.flaminsystems.com>
RE: Burned out new 340 hp motor
Please describe the damage - ie. 1, 2 or 3 phases destroyed, what type of failure etc.
Why didn't the protection gear catch it ?? unless itwas a major winding fault.
But need more info.
Naresuan University
Phitsanulok
Thailand
RE: Burned out new 340 hp motor
The SS starter has numerous safeties such as half phase, phase loss, phase rotation, overload, SCR temp, OOL (?) and several others that does not come to mind.
Single phasing and overload should have been caught by the starter's safeties. I just installed the motor and had no loose connections. "faulty semiconductors in a soft starter", wouldn't you have to lose both half phases in the same phase and at the same time (since the half phase safety did not fault) for the SS starter to cause single phasing? Wouldn't moisture have been an issue in the previously years when the winding insulation was very poor? The motor was rewound since it grossly failed the megging.
RE: Burned out new 340 hp motor
RE: Burned out new 340 hp motor
Just guessing from very limited inof, it smells like a moisture problem to me. You had previous bad meggers on the old motor. Failed shortly after start. Did you ever figure out the cause. Outdoor motor? What enclosure type? What space heaters?
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RE: Burned out new 340 hp motor
If this is a chiller´s motor I think is a special motor called hermetic, this kind of motors are mounted hanged on the chiller(are not a external motor´s) this motor are not fan ventilated and are cooled by the same refrigerant, due to the motor´s design are smallest than standard motors.
If the above is your case, ask to the shop if they was made a VPI Process to the stator winding is not this is the failure cause.
Due to the motor´s small size, this kind of motors experiment more mechanicall stress by magnetic forces and is necessary to add strenght to the windings, take acount too the shop need to use hermetic materials in order to wound the stator.
Regards
Petronila
RE: Burned out new 340 hp motor
RE: Burned out new 340 hp motor
pbcd;
Re petronila's post;
Is this a semi hermetic or an external motor?
yours
RE: Burned out new 340 hp motor
In your case however, since you were able to start it prior to it failing, this was most likely NOT the case, otherwise the SS starter would have locked you out from starting at the very least (there is no way of knowing if an SCR is shrted when running, and it makes no difference anyway). The only possibility is if someone disabled the Shorted SCR protection feature and it did not have Shunt Trip protection. Post your SS starter brand and model and I can tell you for sure what type of protection is has and how to tell if it was disabled.
Once your motor is at full speed, the SS starter is really no different that any other starter, in fact it most likely has a bypass contactor anyway. I seriously doubt it had any role in the motor damage.
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RE: Burned out new 340 hp motor
"burnt-out" - motor sparked and smoked
Motor shop will open motor and inspect in a few days. Not sure how conclusive the findings will be.
This is a York chiller with an open motor (external) and is located in a machinery space. No space heaters - Hawaii.
SS starter also made by York. Will obtain mod #.
No bypass contactors are used.
jraef: I was under the impression that in order to single phase, both SCRs would have to fail on the "same" phase?
Also posted my question in the Solid State forum.
Thanks guys!
RE: Burned out new 340 hp motor
The failure most be analysed in detail by the repair shop,the electric motor´s failures are consecuence of many factors: electrical, mechanical, enviromental, missalignment and mounting failures,power quality,etc. For it the shop most be conclusive with the root failure cause sending a complete technical report including all mechanical fits at shaft and bearing housings,stator loop test, bearings diagnostic and supporting all with pictures.
The most failure types are ilustrated in detail by the most OEM or repair shop and this pictures will give you a forensic idea. This link could help you: www.firstelectricmotor.com (Look for motor´s failure).
Regards
Petronila
RE: Burned out new 340 hp motor
In general, If you're close to the motor you pretty much know it if a soft-starter is acting up. The motor will sound alful and likely won't accelerate or accelerate really badly.
As the others have posted, get the motor analyzed first to see why it failed then investigate the starter if it's necessary.
RE: Burned out new 340 hp motor
Keith Cress
Flamin Systems, Inc.- http://www.flaminsystems.com
RE: Burned out new 340 hp motor
If this is an open motor (vs TEFC) I would look very very closely at moisture. If TEFC, you may subtract one very.
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RE: Burned out new 340 hp motor
Relative humudity is more important than temperature in regards to condensation.
About six months ago I got a flight out to a Caribean island. The plant operator reported that the strip heaters had failed on a 1.6 MW diesel generator. The utility general manager understood the possible consequences. I flew out in the morning, and spent an hour or so repairing a loose connection on one terminal of a strip heater. The heat corrosion had burned through one of the wires. I repaired everything and spent the afternoon sightseeing and visiting old aquantances. I had a good supper and a good hotel room. Flew home in the morning.
What electricpete said.
Hawaii is probably more at risk for condensation issues than most of Canada and the Northern two thirds of the U.S.
Machine rooms in Canada and the US tend to be enclosed and heated.
Machine rooms in the tropics tend to have wide open windows and doors and lots of flow through ventilation. Not always, but often.
respectfully
RE: Burned out new 340 hp motor
The reason I doubted that the SS starter was your cause, is that the shorted SCR detection (which works by looking for a lack of a voltage drop across the SCR stack), would have prevented you from restarting that chiller had there been even one shorted SCR, let alone 2. The York SSS does have shorted SCR detection by the way, but not shunt trip. You are correct that they don't have a bypass contactor because they use a water cooled heat sink (shudder).
While I really think it wisest for you to have your motor professionally analyzed, here is a decent primmer on common modes of winding damage to see if it is anything obvious.
EASA winding damage failures
Eng-Tips: Help for your job, not for your homework Read FAQ731-376
RE: Burned out new 340 hp motor
The gate drive circuit could also have an issue and not fire one or more of the SCR's. This leads to at least 1/2 of a phase missing. Once again, this is a condition that is very apparent if you try to start the motor with the failure. If the motor is running it should stall or current imbalance bad enough that the protection picks-up.
RE: Burned out new 340 hp motor
Agreed, however remember this was a 340HP motor; bricks don't go that high. I have yet to see a completely evaporated hockey puck. I've seen the sides blown out but they were still conductive. Maybe I'm just lucky!
You're also right about the gate failure possibility, however rare that would be. It's highly unlikely that it would start with a failed gate, but if it failed while running that would be another story because the unbalance and DC component in the windings would be very high, leading to rapid overheating that may not be picked up by the Overload Relay fast enough. I hadn't thought that through because I'm a firm believer in bypass contactors, in which case you never know if a gate failed while running. Still, 4 minutes to failure? That's extremely fast for a motor that size.
It still seems like an unrelated motor failure to me.
Eng-Tips: Help for your job, not for your homework Read FAQ731-376
RE: Burned out new 340 hp motor
The result of this is one phase running half wave and effectively injecting DC into the motor windings. The high increase in current results in sever vibration in the motor and the breaker on the line side trips. I have come across a batch of faulty H Puck SCRs where the gate became intermittant when the puck was up to temperature. The starter would start fine (except for high inertia starts and then play up after a period of operation. I had to heat the SCRs up to prove that the gate was internally intermittant. - never lost a motor due to this, always tripped the starter on imbalance, or tripped the breaker.
The standard shorted SCR failure would not cause an issue with the motor while running. If the SCR failed before the start, the motor either would not start due to the protection, or would give an obvious very rough start and probably trip some protection somewhere.
Best regards,
Mark Empson
http://www.lmphotonics.com
RE: Burned out new 340 hp motor