# Motor problem



## GEORGE D (Apr 2, 2009)

About a month ago I upgraded four 460v 3ph 17hp vacuum motors for an industrial plant. Got a call saying one burned up so I went to see. In it's place was the older motor hooked up and running. Maintenance had changed it out temporarily. They said they found the breaker tripped. None of the overloads blew or fuses popped. Long story short the manufacturer took it, evaluated it and said there was a voltage spike on one of the legs. There are about three panels on this same transformer with more motors and quite a bit of machines/equipment and nothing was affected. Doesn't sound right to me, what do you guys think?


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## John Valdes (May 17, 2007)

17 HP is not a standard motor size so you must have OEM vacuum pump motors, right? The ones you upgraded are rated for this duty? They are supplied by the manufacturer?

The manufacturer cannot say for sure that a voltage spike took out one leg or winding. They can see a bad winding but they cannot tell you why.

Make sure all the motors you used for the upgrade are designed for this purpose. Have the motor that failed checked by an EASA accredited motor shop. Let them determine the cause if they can. They can also double check that you have the correct motors for the application. 

I would also double check the breaker. Could be a defective breaker that caused the motor to fail.

Lastly. Motors fail. New ones and old ones. Just because you installed these motors recently, does not guarantee the motor was not the problem.


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## Jefro (Jul 28, 2009)

That does sound a little hinky for maintenance to just replace it because the breaker tripped. A conductor could have just grounded out in the peckerhead or something. Check the OL, if it's adjustable, for the proper amp setting (or heater size). You never know who was in there after you. And maybe meg the motor and check leads from the OCPD, too...


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## Zog (Apr 15, 2009)

John Valdes said:


> I would also double check the breaker. Could be a defective breaker that caused the motor to fail.


Sounds like the breaker did it's job.


GEORGE D said:


> They said they found the breaker tripped. None of the overloads blew or fuses popped.


How exactly would a breaker cause a motor to fail anyways?


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## John Valdes (May 17, 2007)

Zog said:


> Sounds like the breaker did it's job.
> 
> How exactly would a breaker cause a motor to fail anyways?


A high resistance connection across the internal breaker terminal or terminals. Voltage shows as present until load is applied. Then motor single phases and takes it out. Thats how.

This does not show as an overload condition and thats why the Ol's did not respond. The current would be fine on two legs and the current on the bad leg would be zero.


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## GEORGE D (Apr 2, 2009)

Just letting you guys know that they didn't blame me, although I'm sure they would love to considering these are 10,000$motors. The supervisor thinks we should maybe look into some type of spike filters for all motors which I assume would just be isolation xformers but I think it's not necessary.


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## GEORGE D (Apr 2, 2009)

Oh and the OL's are non adj, and absolutely no sign of short circuit anywhere including peckerhead.


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## Jlarson (Jun 28, 2009)

I'd do a FOP test on the breaker and starter, meg all the conductors out, and maybe put a logger on to see if there is any truth to this "spike" idea but that's probably just BS from the manufacturer. 

It could very well have just been a bad motor out of the box with a compromised winding.


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## John Valdes (May 17, 2007)

Jlarson said:


> I'd do a FOP test on the breaker and starter, meg all the conductors out, and maybe put a logger on to see if there is any truth to this "spike" idea but that's probably just BS from the manufacturer.
> 
> It could very well have just been a bad motor out of the box with a compromised winding.


I agree. At the price he mentions these aren't your every day motors either.


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## Motorwinder (Dec 30, 2010)

GEORGE D said:


> About a month ago I upgraded four 460v 3ph 17hp vacuum motors for an industrial plant. Got a call saying one burned up so I went to see. In it's place was the older motor hooked up and running. Maintenance had changed it out temporarily. They said they found the breaker tripped. None of the overloads blew or fuses popped. Long story short the manufacturer took it, evaluated it and said there was a voltage spike on one of the legs. There are about three panels on this same transformer with more motors and quite a bit of machines/equipment and nothing was affected. Doesn't sound right to me, what do you guys think?


Electricity is a funny thing. That spike went right to the weak spot in the winding.


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## McClary’s Electrical (Feb 21, 2009)

GEORGE D said:


> Oh and the OL's are non adj, and absolutely no sign of short circuit anywhere including peckerhead.


 

Strictly out of curiousity, what are the overloads set at for a 17 hp motor?


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## Thedroid (Dec 6, 2010)

John Valdes said:


> A high resistance connection across the internal breaker terminal or terminals. Voltage shows as present until load is applied. Then motor single phases and takes it out. Thats how.
> 
> This does not show as an overload condition and thats why the Ol's did not respond. The current would be fine on two legs and the current on the bad leg would be zero.



The current on the other two phases would be much higher than normal. If the current was fine, than single phasing would not burn up motors.

I do agree that a high resistance contact in the breaker could cause damage to an improperly protected motor, but I don't think that this was the case. If the contact resistance in an MCCB is high enough to cause a motor to single phase, its going to create a lot of heat, and probably won't fix itself.

10g's for a 17hp motor. Wow!! Vacuum pumps aren't that special. Who makes this motor, and who makes the originals?


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## Jlarson (Jun 28, 2009)

GEORGE D said:


> About a month ago I upgraded...


I take it you didn't megger the new motors before you installed them?


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## mrmike (Dec 10, 2010)

We never meggar small motors like this before installing them but did for 100hp & up. I think that I would have in this case if that is truly the cost of it. I don't believe it was a spike but a faulty motor, especially as you said nothing else was affected. I have seen motor fry as soon as you start them -especially if they had condensated inside- yes water will do it every time--- & it is instaneous so just the breaker trips..................


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## GEORGE D (Apr 2, 2009)

mcclary's electrical said:


> Strictly out of curiousity, what are the overloads set at for a 17 hp motor?


I believe we used the next listed hp size which was 20 if I'm not mistaking and ol I think was +-32 amps. Its been several jobs ago but I think this info is about right. Can someone check that out?


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## Jefro (Jul 28, 2009)

GEORGE D said:


> Oh and the OL's are non adj, and absolutely no sign of short circuit anywhere including peckerhead.


I know I probably missed it, but is the motor actually bad? Grounded on one lead? No continuity through two of the leads?


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## micromind (Aug 11, 2007)

If the motor is on a VFD, and it isn't designed for it, spikes will certainly be present; especially if the motor is some distance from the VFD. 

These spikes will eventually go through the insulation and you'll have an internal fault that a megger might not catch.


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## MDShunk (Jan 7, 2007)

micromind said:


> If the motor is on a VFD, and it isn't designed for it, spikes will certainly be present; especially if the motor is some distance from the VFD.
> 
> These spikes will eventually go through the insulation and you'll have an internal fault that a megger might not catch.


It's not your every day electrician who will have the ability to check for turn to turn faults on new and existing motors, but an industrial facility with hundreds of motors might be well-served by having equipment to check the motors for turn to turn and winding imbalances at low levels so that they can plan their outages.


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## Jlarson (Jun 28, 2009)

mrmike said:


> We never meggar small motors like this before installing them but did for 100hp & up.


I meg just about every motor before I install it, same with transformers and feeder pulls before I energize. Oh god I'm turning into MD :laughing:


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## Motorwinder (Dec 30, 2010)

Thedroid said:


> The current on the other two phases would be much higher than normal. If the current was fine, than single phasing would not burn up motors.
> 
> I do agree that a high resistance contact in the breaker could cause damage to an improperly protected motor, but I don't think that this was the case. If the contact resistance in an MCCB is high enough to cause a motor to single phase, its going to create a lot of heat, and probably won't fix itself.
> 
> 10g's for a 17hp motor. Wow!! Vacuum pumps aren't that special. Who makes this motor, and who makes the originals?


Single phasing will definitely burn up a motor.


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## Motorwinder (Dec 30, 2010)

micromind said:


> If the motor is on a VFD, and it isn't designed for it, spikes will certainly be present; especially if the motor is some distance from the VFD.
> 
> These spikes will eventually go through the insulation and you'll have an internal fault that a megger might not catch.



Most new motors are wound with spike resistant wire.


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## millelec (Nov 20, 2010)

Thedroid said:


> 10g's for a 17hp motor. Wow!! Vacuum pumps aren't that special. Who makes this motor, and who makes the originals?


We have Trane Absorption Chillers for A/C. The main pump motor for it was 10 HP, and is no longer available. Last I knew we had to either upgrade to 15 HP or hope someone had an old motor on shelf. they were running $20-25K each while we still could get them.


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## Jefro (Jul 28, 2009)

I was thinking, Is there any kind of control voltage transformer in the cabinet on that breaker for, say, the motor starter?


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## mrmike (Dec 10, 2010)

Jlarson said:


> I meg just about every motor before I install it, same with transformers and feeder pulls before I energize. Oh god I'm turning into MD :laughing:


 
This was just our "standard" policy in our plant. Same with feeders- usually just the bigger ones.......
If I were a small co. installing them, I would then meggar most to protect myself.......


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## John Valdes (May 17, 2007)

Motorwinder said:


> Most new motors are wound with spike resistant wire.


True. Baldor was one of the first to do it across the board.

Do you wind armatures and AC coils in your shop? Are you actually a winder? I used to work in a motor shop and was always impressed with the winders. In the shop I worked in the AC motor winders did not work on the DC end, only the AC. But both DC guys were capable of taking the AC guys place anytime.
Do you use 1600 volt magnet wire and class "H" insulations on your rewinds? Do you use phase paper between phases. 
You do know that "Spike Resistant" is trademarked by Baldor? Everyone else has it too, but cannot call it "Spike Resistant".


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## Motorwinder (Dec 30, 2010)

John Valdes said:


> True. Baldor was one of the first to do it across the board.
> 
> Do you wind armatures and AC coils in your shop? Are you actually a winder? I used to work in a motor shop and was always impressed with the winders. In the shop I worked in the AC motor winders did not work on the DC end, only the AC. But both DC guys were capable of taking the AC guys place anytime.
> Do you use 1600 volt magnet wire and class "H" insulations on your rewinds? Do you use phase paper between phases.
> You do know that "Spike Resistant" is trademarked by Baldor? Everyone else has it too, but cannot call it "Spike Resistant".


Our shop winds everything except transformers.

I'm the shop foreman where I work (working foreman), and do all the data confirmations. I've been an armature ( and AC)winder for 36 years, in the trade for 38 years. Wound motors up to 13.8 KV 10,000HP, but was always the armature/ DC specialist in the shops I worked at. 

Not sure of the voltage rating of the magnet wire we use, but it's quad build VFD duty Essex wire. 

We wind class H except for the leads. Which we will when requested. Some customers hate that silicon/glass lead wire. We phase insulate anything over 1.5hp, or where the motor runs around a lot of moisture. We also check the volts per coil on the larger HP motors, and will insulate between each coil if the volts are over 70 volts per coil.


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## John Valdes (May 17, 2007)

Motorwinder said:


> Our shop winds everything except transformers.
> 
> I'm the shop foreman where I work (working foreman), and do all the data confirmations. I've been an armature ( and AC)winder for 36 years, in the trade for 38 years. Wound motors up to 13.8 KV 10,000HP, but was always the armature/ DC specialist in the shops I worked at.
> 
> ...


I know you are a motor guy. :thumbsup: You are in zero company here except maybe one other member I can think of. But I am glad you are here! You are going to be a big help. 

I was technical sales rep at the shop I worked for. So I only know what I saw, over the 7 years I was there. I did run the complete shop for 6 months when we had a special need. That was one of the hardest jobs I ever had. The customers will drive you nuts and the emergency work was ready to kill me. 
Are you guys an EASA shop? Welcome to the forum and sorry I did not see your response until just now.


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## McClary’s Electrical (Feb 21, 2009)

Motorwinder said:


> Our shop winds everything except transformers.
> 
> I'm the shop foreman where I work (working foreman), and do all the data confirmations. I've been an armature ( and AC)winder for 36 years, in the trade for 38 years. Wound motors up to 13.8 KV 10,000HP, but was always the armature/ DC specialist in the shops I worked at.
> 
> ...


 


The biggest motor I've been envolved with removing, getting rebuilt, and reinstalling was 2500 HP 4160v. You could stand up inside the Stator with your hands over your head with plpenty of room to spare, once the rotor was removed. I can only imagine the size of a 10,000 HP.


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## Motorwinder (Dec 30, 2010)

John Valdes said:


> I know you are a motor guy. :thumbsup: You are in zero company here except maybe one other member I can think of. But I am glad you are here! You are going to be a big help.
> 
> I was technical sales rep at the shop I worked for. So I only know what I saw, over the 7 years I was there. I did run the complete shop for 6 months when we had a special need. That was one of the hardest jobs I ever had. The customers will drive you nuts and the emergency work was ready to kill me.
> Are you guys an EASA shop? Welcome to the forum and sorry I did not see your response until just now.


Yes, we're an EASA shop.

When I saw you guys started a motor and control forum, I figured I'd chime in.
Thanks for the welcome.


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## John Valdes (May 17, 2007)

mcclary's electrical said:


> The biggest motor I've been envolved with removing, getting rebuilt, and reinstalling was 2500 HP 4160v. You could stand up inside the Stator with your hands over your head with plpenty of room to spare, once the rotor was removed. I can only imagine the size of a 10,000 HP.


That is one hell of a motor Jerry. We could work on that size in our shop. Amazing how big a 2500 HP motor really is.



Motorwinder said:


> Yes, we're an EASA shop.
> 
> When I saw you guys started a motor and control forum, I figured I'd chime in.
> Thanks for the welcome.


Cool. I used to go to all the EASA conventions all over the country. We also used Essex for magnet wire and insulating supplies. Essex sent my boss and his wife to Alaska on a special deal. Free.
You see we had two shops, so our buying power was pretty good. 

I worked for Crimson Electric in Greer SC. Our other shop was Rome Electric in Rome GA.

Do you guys replace more that you rewind? We were at a 60-40% with the 60% being new replacement. I am sure by now they are even more towards replacement. Do you guys do power transmission too? Gearing and drives?
Some other shops do not even look at anything under 100 HP, unless its an OEM special, or old enough its not available anymore.

We worked on most anything and almost became known as a pump repair shop. We did tons of pumps for the municipalities in the area. Lots of vertical hollow shaft and aerators.

I did the controls end along with the ISO and safety. This was in addition to a regional territory I was responsible for. Like I said, it was a hard job. But fun.


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## Zog (Apr 15, 2009)

Small world John, I was just at the EASA meeting last month in Asheville, some Crimson guys were there too.


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## John Valdes (May 17, 2007)

Zog said:


> Small world John, I was just at the EASA meeting last month in Asheville, some Crimson guys were there too.


Do you know Charles Wilson? The President of Crimson? It is a small world. And yes, we always went to EASA functions when we could. Last one I was at was in Myrtle Beach. About 6 years ago.

I have been gone from Crimson since 2005. Thats where I got hurt. They were my best friends until then.


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## JRaef (Mar 23, 2009)

Just FYI for everyone who was curious...

17HP is 22kW. 22kW is a fairly standard IEC motor size. But a lot of mfrs make a mistake about this actually. If it was a 22kW 380V 50Hz motor, and it is sent to the US and given 480V 60Hz, it will work fine and provide the same torque, but in reality the HP actually goes up by 20% because the speed is 20% faster (HP is a function of speed and torque). So really, they are probably closer to 20HP. Sometimes a machine OEM will know this and chose to ignore it, assuming that the user will not care as long as the machine works. 

It also could be the other way around as well. It could be that they used 18.5kW 380V 50Hz motors, another common size and when they are given 480V 60Hz, the kW goes up 20% again, which is 22kW or 17HP. Again, it's not important if the machine works.

It's just an important consideration if those motors need to be replaced or used elsewhere.

And by the way, OL heaters should ONLY be selected based on motor nameplate FLA, never on HP size. A slight mismatch on a heater element (or setting) can lop off a LOT of motor insulation life.


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## McClary’s Electrical (Feb 21, 2009)

John Valdes said:


> That is one hell of a motor Jerry. We could work on that size in our shop. Amazing how big a 2500 HP motor really is.


 

It is amazing how huge they are. Very impressive. The motor is still in operation today. The biigest generator I've been involved with installing was rated for 1 mw, but we ran it at 900-950kw most of the time.


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## McClary’s Electrical (Feb 21, 2009)

Motorwinder said:


> Yes, we're an EASA shop.
> 
> When I saw you guys started a motor and control forum, I figured I'd chime in.
> Thanks for the welcome.


 
OK question. How much clearance (air gap)should a 2500 HP motor 4160 volt, 350 RPM , have between the rotor and stator? When this 2500 came back from the shop and we cranked it up, once it got to a certain speed, it would develope a slight "wobble" and the rotor would hit the stator while it was running. The sound was ever so slight that most people didn't catch it. So, we started checking air gaps and found it slightly off center, but mainly we were guessing the steel that the stator is mounted to is flexing due to magnetic force. We find that with dial indicator set up on the frame while running, it indeed IS flexing. WE have a welder come in and gusset up under the stator frame on both side. That satisfies the movement of the stator. Now set air gap perfectly, crank up motor. Starts knocking again. Shut down, check air gap, it's changed again. Bearing tolerances were all fine and checked by a millwright. Change ramp speed in liquid reastat seems to help. Shaft seems to be flexing, then that develops a wobble, and slowly gets worse. The air gap was less that .125"
I argued with the motor rewinder that that was not enough clearance for a motor with a 16" diameter shaft 25' long. What's your take?


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## John Valdes (May 17, 2007)

mcclary's electrical said:


> OK question. How much clearance (air gap)should a 2500 HP motor 4160 volt, 350 RPM , have between the rotor and stator? When this 2500 came back from the shop and we cranked it up, once it got to a certain speed, it would develope a slight "wobble" and the rotor would hit the stator while it was running. The sound was ever so slight that most people didn't catch it. So, we started checking air gaps and found it slightly off center, but mainly we were guessing the steel that the stator is mounted to is flexing due to magnetic force. We find that with dial indicator set up on the frame while running, it indeed IS flexing. WE have a welder come in and gusset up under the stator frame on both side. That satisfies the movement of the stator. Now set air gap perfectly, crank up motor. Starts knocking again. Shut down, check air gap, it's changed again. Bearing tolerances were all fine and checked by a millwright. Change ramp speed in liquid reastat seems to help. Shaft seems to be flexing, then that develops a wobble, and slowly gets worse. The air gap was less that .125"
> I argued with the motor rewinder that that was not enough clearance for a motor with a 16" diameter shaft 25' long. What's your take?


Jerry, He cannot answer that question without knowing who the motor manufacturer is and the specs. He may be able to give you a ball park measurement, but on a motor this size it would be nuts to guess the air gap.
This gap is set at the factory and cannot be adjusted in any way. 
The first thing I would do is get the rotor balanced. If all the machine work is okay, this motor should have not been assembled without balancing. Have you had it balanced?

I hope they did not stick the rotor in backwards? I have seen this done before. This would mess up the alignment. 
Lets see what the new guy has to tell us.

Ps.......Have you checked the rotor for a loose bar? The rotor can be tested with a core tester and some metal filings. I have seen loose bars before also. They are hard to see. You need to mechanically check this rotor and check it electrically too. You might just have a bar that has come up just enough to cause your issue.

Whos the shop doing this work? You can PM me if you do not want to say here in public. Is it SESCO?


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## Motorwinder (Dec 30, 2010)

Sounds more like a balance problem. I'm guessing this is a synchronous motor with rotating fields. The rotor bars are for starting only.

.125" sounds about right. Why it's changing? Rotor could be loose on the shaft and causing some wobble. Could be running in a critical frequency, and needs more gusseting to add mass and change the critical. Could have a soft foot condition, and the stator is moving. Make sure the bolts are torqued to the german toque factor, gudentite.

25' long shaft is between the bearings?

You might want to get the motor a vibration analysis. 

Hard to tell without looking it over.


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## McClary’s Electrical (Feb 21, 2009)

Motorwinder said:


> Sounds more like a balance problem. I'm guessing this is a synchronous motor with rotating fields. The rotor bars are for starting only.
> 
> .125" sounds about right. Why it's changing? Rotor could be loose on the shaft and causing some wobble. Could be running in a critical frequency, and needs more gusseting to add mass and change the critical. Could have a soft foot condition, and the stator is moving. Make sure the bolts are torqued to the german toque factor, gudentite.
> 
> ...


 

No, that's total length. Probably 15'-18' between bearings. Thanks for your opinion:thumbup:


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## McClary’s Electrical (Feb 21, 2009)

John Valdes said:


> Jerry, He cannot answer that question without knowing who the motor manufacturer is and the specs. He may be able to give you a ball park measurement, but on a motor this size it would be nuts to guess the air gap.
> This gap is set at the factory and cannot be adjusted in any way.
> The first thing I would do is get the rotor balanced. If all the machine work is okay, this motor should have not been assembled without balancing. Have you had it balanced?
> 
> ...


 

Thanks John:thumbup: Electrical Equipment rewound the motor, Nicky Allen did the balancing and alignment.


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