# Star connection on motor termination burning open.



## just the cowboy (Sep 4, 2013)

What is the current compared to the nameplate. 
Has the motor ever been rewound.
If rewound what was the service factor and did they rewind it to that.

The reason I asked those questions is because I had a 480 volt 125 HP compressor. The manufacture did not make a 125hp. motor they made a 100hp. at a 1.25 service factor. They designed the system at 1.25 SF and that was missed twice, once by the installer he sized it for 100hp. service. Second time was by the motor shop that rewound it.

Vibration also, it is a compressor.

Cowboy

PS Welcome please get back to us with the outcome if you find it so others can learn.


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## micromind (Aug 11, 2007)

How is the connection made? 

Crimp lugs and a bolt? Split bolt? A Polaris type splice?

Is there a huge gob of tape on it so the heat cannot dissipate?

Is the splice up against the frame and overheats?

What about wire size? the current on this motor will be somewhere around 140 - 150 amps, if it's something like a #2 @250C, if so, it'll run pretty hot naturally.

One thing to remember about splicing the center of a Y, the voltage to ground is low, even at 4160, it'll be less than 500 volts. There's no need for 53 layers of 130C and whatever else it's wrapped with. The more tape it's wrapped with, the more heat will build up inside.


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## 460 Delta (May 9, 2018)

Is this a 6 lead motor or a 3 lead motor, where the star is made up inside? I suppose for ultimate durability you may be able to Cad-Weld it together.


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## just the cowboy (Sep 4, 2013)

Since he said Wye and common connection I would guess 9 lead with internal common connection. From doing motor rewinds that is not an easy connection to redo if it burnt open at one time. My guess is bad repair and this one will last less time. @wfodonne If this is dual volt motor and you end up getting it rewound have them rewind it single voltage, less chance of a connection failure in the future.

Cowboy


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## micromind (Aug 11, 2007)

460 Delta said:


> Is this a 6 lead motor or a 3 lead motor, where the star is made up inside? I suppose for ultimate durability you may be able to Cad-Weld it together.


Most likely 6 lead. 2400/4160.

For 2400, it's connected ∆, for 4160, it's Y.


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## paulengr (Oct 8, 2017)

OK, where are the photos? It's hard to inspect/diagnose anything with a totally generic "my leads burned up" complaint. You have to carefully take everything apart. Look for arc tracks, tracking damage, any signs of insulation erosion (white powder), discoloration, cracked or melted insulation, rub marks, fitting looseness. It's preferable that there are before/after/during disassembly photos all along the way. If there is any semicon on the wiring, pay particular attention to it. That's on top of the usual concerns about splicing and how that is done that applies to ANY motor. Practices that are perfectly fine that you can get away with at 480 V are totally unacceptable for medium voltage and it gets progressively and rapidly worse as you go from 2400 to 4160 to 7200 to 11 kV to 25 kV to 35 kV. Each step along the way forces you to improve your technique. Taking it apart often destroys evidence so call a medium voltage motor tech to inspect BEFORE you take it apart. This is even worse when it's medium voltage because voltage flux problems are an issue not just thermal ones like they are at lower voltages. You need to take the motor to a reputable electric motor repair shop for a full diagnosis and have THEIR crews make the repairs. I've seen lots of repairs done by electricians or engineers that think they know what they are doing but if they can't point to a procedure from the manufacturer of the materials that they are using and can tell you why they are doing what they are doing, you get what you pay for. Then I come back a couple months later and clean up all the damage and do it the way it should have been done in the first place.

As an example of the kinds of things that matter at medium voltage but not at 480, most electricians not only put a gazillion layers of tape on everything as mentioned but also understand what partial discharge is which is a common issue. The dielectric (insulation rating per inch) of most insulation materials is 3-5 times higher than air. So if you don't stretch the tape as per manufacturers instructions and leave an air void, you develop a much higher voltage stress around that air void. This causes internal arcing (corona discharge) hidden under the tape that you can't see. When it arcs the surface is damaged and becomes semi-conductive as well as opening up the air void further. Then another arc opens the gap up even further until it fails over time. Medium voltage motor insulation is VPI'd specifically because this used to be a big problem within the motor insulation itself. So if the electrician just sort of "lays" the tape up without stretching it a LOT you will get air pockets and voids which causes premature failures. Another big problem is how close the leads are to each other. As mentioned the wye should be close to ground even if it's not actually grounded but it is at least 2300 V from the nearby phase leads so they need to be laid out so that they can breathe and not rub against each other just as at 480 V but also so that they don't cause high voltage stress between leads. And that doesn't even get into the splice itself. At the wye you have about 2/3rds of the force generated by the motor on the leads attempting to rip that splice apart, plus thermal heating and contraction going on which is the reason that mechanical splices are simply unacceptable. If it isn't well made it can easily mechanically rip itself apart over time. Another big issue is the type of crimp or mechanical splice itself. Most motor leads are fine strand wire. This means you need a fine strand connector. If you use the more common coarse strand ones, they tend to cut into the strands or don't hold them properly, leading to failures.

The big thing here though is experience and technique. I don't care how many engineers you have standing around looking like they know what they are doing. My work will outlast the motor where you might only get a couple years out of it. My whole crew does this kind of work all the time. If anything at all changes in what we are doing or anyone else, we see the after effects almost immediately. We've all been trained by 3M engineering. We watch each other. We also see lots of screw ups from not only other electricians but from motor shops. So we get tons of practice dealing with this very issue over and over again, even if we didn't do it. We have an ISO 9000 system in place at our shop. Every mistake gets the full proctological so issues are quickly identified and eliminated. As an example unless the customer insists on it, I would be given time off it not fired if I was caught using wire nuts, split bolts, or Polaris taps on motor leads. Although these CAN work our experience is that the failure rate is so high we don't risk it. I carry a bunch of wire nuts on the van as temporary terminations and testing tools only, not permanent.

Four things to look for in a motor shop service crew for this kind of work. The first one is do they have a field service crew? Don't bother with the ones that do everything in a shop environment and never get out of the office. I don't mean a couple guys from the shop, I mean full time on the road field service crew(s). Second is do they have an ISO 9000 or EASA third party annual inspection and a fully documented corrective action procedure? Third item is do they have a clean room capable of 10 kV+ motor winding. This seems like overkill for you but anything you do at higher voltages forces you to do a better job and that trickles down to lower voltages since there is no extra work involved in making a 4160 termination...you get the 11 kV splice quality for the 4160 V motor, too. Fourth is can you independently verify that they are an authorized service center for one or more motor brands? Motor manufacturers rarely actually service their product. They use a local motor shop for that but they are picky who they use. So if they sell say Toshiba brand, are they listed as a service center with Toshiba? So you can independently use the motor manufacturer's recommendations as further evidence of a quality shop. Don't get hung up on brand naes though...even if you are dealing with a GE motor the fact that they are a Toshiba or Westinghouse shop doesn't matter. It's the fact that the motor manufacturer vetted them that's important. With these 4 criteria I can tell you right now you are only going to find 1 or 2 shops in a region and often the entire state that meet this criteria.

Chances are you are going to pay several hundred dollars for a tech from this kind of company to come out and redo it for you. It all depends on what your downtime is worth.


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## joe-nwt (Mar 28, 2019)

That's it? That's all you have to say?

J/K. Thanks for the informative post!


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## wfodonne (May 13, 2021)

just the cowboy said:


> Since he said Wye and common connection I would guess 9 lead with internal common connection. From doing motor rewinds that is not an easy connection to redo if it burnt open at one time. My guess is bad repair and this one will last less time. @wfodonne If this is dual volt motor and you end up getting it rewound have them rewind it single voltage, less chance of a connection failure in the future.
> 
> Cowboy


It’s 6 lead, with the 3 common on the outside .thanks for the help!


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## wfodonne (May 13, 2021)

Ok


micromind said:


> Most likely 6 lead. 2400/4160.
> 
> For 2400, it's connected ∆, for 4160, it's Y.


six lead


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## wfodonne (May 13, 2021)

micromind said:


> How is the connection made?
> 
> Crimp lugs and a bolt? Split bolt? A Polaris type splice?
> 
> ...


Crimp lugs and bolts. We didn’t over do the tape. We did line the termination box with rubber sheets to keep the connections clear. Wire sizing is good.
Thanks!


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## wfodonne (May 13, 2021)

just the cowboy said:


> Since he said Wye and common connection I would guess 9 lead with internal common connection. From doing motor rewinds that is not an easy connection to redo if it burnt open at one time. My guess is bad repair and this one will last less time. @wfodonne If this is dual volt motor and you end up getting it rewound have them rewind it single voltage, less chance of a connection failure in the future.
> 
> Cowboy


Thanks!


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## wfodonne (May 13, 2021)

paulengr said:


> OK, where are the photos? It's hard to inspect/diagnose anything with a totally generic "my leads burned up" complaint. You have to carefully take everything apart. Look for arc tracks, tracking damage, any signs of insulation erosion (white powder), discoloration, cracked or melted insulation, rub marks, fitting looseness. It's preferable that there are before/after/during disassembly photos all along the way. If there is any semicon on the wiring, pay particular attention to it. That's on top of the usual concerns about splicing and how that is done that applies to ANY motor. Practices that are perfectly fine that you can get away with at 480 V are totally unacceptable for medium voltage and it gets progressively and rapidly worse as you go from 2400 to 4160 to 7200 to 11 kV to 25 kV to 35 kV. Each step along the way forces you to improve your technique. Taking it apart often destroys evidence so call a medium voltage motor tech to inspect BEFORE you take it apart. This is even worse when it's medium voltage because voltage flux problems are an issue not just thermal ones like they are at lower voltages. You need to take the motor to a reputable electric motor repair shop for a full diagnosis and have THEIR crews make the repairs. I've seen lots of repairs done by electricians or engineers that think they know what they are doing but if they can't point to a procedure from the manufacturer of the materials that they are using and can tell you why they are doing what they are doing, you get what you pay for. Then I come back a couple months later and clean up all the damage and do it the way it should have been done in the first place.
> 
> As an example of the kinds of things that matter at medium voltage but not at 480, most electricians not only put a gazillion layers of tape on everything as mentioned but also understand what partial discharge is which is a common issue. The dielectric (insulation rating per inch) of most insulation materials is 3-5 times higher than air. So if you don't stretch the tape as per manufacturers instructions and leave an air void, you develop a much higher voltage stress around that air void. This causes internal arcing (corona discharge) hidden under the tape that you can't see. When it arcs the surface is damaged and becomes semi-conductive as well as opening up the air void further. Then another arc opens the gap up even further until it fails over time. Medium voltage motor insulation is VPI'd specifically because this used to be a big problem within the motor insulation itself. So if the electrician just sort of "lays" the tape up without stretching it a LOT you will get air pockets and voids which causes premature failures. Another big problem is how close the leads are to each other. As mentioned the wye should be close to ground even if it's not actually grounded but it is at least 2300 V from the nearby phase leads so they need to be laid out so that they can breathe and not rub against each other just as at 480 V but also so that they don't cause high voltage stress between leads. And that doesn't even get into the splice itself. At the wye you have about 2/3rds of the force generated by the motor on the leads attempting to rip that splice apart, plus thermal heating and contraction going on which is the reason that mechanical splices are simply unacceptable. If it isn't well made it can easily mechanically rip itself apart over time. Another big issue is the type of crimp or mechanical splice itself. Most motor leads are fine strand wire. This means you need a fine strand connector. If you use the more common coarse strand ones, they tend to cut into the strands or don't hold them properly, leading to failures.
> 
> ...


Great information. We did not splice on more wire, but tied the star common back together with crimp lugs and bolts. From what you say it sounds like our taping could be the issue. The motor has never been serviced since installation, but i will recommend servicing. I will pass on your shop information to our reliability crew.
Thanks so much!!


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## paulengr (Oct 8, 2017)

wfodonne said:


> Great information. We did not splice on more wire, but tied the star common back together with crimp lugs and bolts. From what you say it sounds like our taping could be the issue. The motor has never been serviced since installation, but i will recommend servicing. I will pass on your shop information to our reliability crew.
> Thanks so much!!


Contact 3M about specific procedures. Remember that you are running on the ragged edge of the limits of what insulation can withstand. ANY high stress area (intentional of unintentional) leads to early failures. So good technique is critical to success.


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