# Motor help



## mattsilkwood (Sep 21, 2008)

About a year ago we installed a big ammonia compressor with a 700hp 480vac motor.

It has three sets of 500mcm running to it about 75' from the drive. 
The 500s are going to a tap box right above the peckerhead and makeup to 3 sets of 350 DLO cable. 
The DLO then goes to the peckerhead and makes up to the motor leads using polaris taps.

About six months into service it bunrt the leads to B phase. 
The drive meters and logs voltage and current among other things, everything looked fine on the log so we chalk it up to a loose connection.
I personally put it all back together, checked and rechecked every connection from the switchgear on down. 

A couple months pass and it does the same thing. Same phase. 
This time we took the motor off and sent it to the motor shop, they went through it and said it was in perfect condition. 

This whole time the maintenance dept has been doing weekly PM which has consisted of shooting all the connections with a thermal gun while it is running and powering down and looking at all the connections for obvious signs of trouble. Everything has always been great. 

Last night the drive faulted out because it lost its network connection, this is the first time it has done this. 
Today we went in and checked everything and just like always everything looks fine. 
We did put our recording meter on thinking the drives metering system isn't reading true.

Does anyone have any ideas about what could be causing this? 

Im looking for any and all ideas, at this point we are chasing our tail.


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## professor poptart (Mar 2, 2010)

Are you thinking the loss of network connection is connected to the other failures? Doubtful. 
As far as the B Phase failure, I don't know. sounds as if you have checked everything thouroghly. 
Where is this failure happening? At the 500 to 350 connection or in the peckerhead?


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## professor poptart (Mar 2, 2010)

Another thing
Make sure the parameters are correctly set in the drive. The motor may be running in a slight overload condition causing a heating failure at the connections. If this a buss type connection B phase will be the hardest to tape and therfore the weakest of the three.
Also could be a control issue if the compressor is cycling too fast, another cause of excessive heating.


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## mattsilkwood (Sep 21, 2008)

I am sure the network connection has nothing to do with it but at this point I'm kinda gunshy.

The fault is happening where the motor leads tap to the 350s.

As far as the heat is concerned, like I said it has been checked every week and always runs right about 95deg F, and no signs of heat. 

I'm stumped.


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## RIVETER (Sep 26, 2009)

mattsilkwood said:


> I am sure the network connection has nothing to do with it but at this point I'm kinda gunshy.
> 
> The fault is happening where the motor leads tap to the 350s.
> 
> ...


If they shot the connections with an IR camera, did you personally look at the images?


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## wwilson174 (Apr 25, 2008)

RIVETER said:


> If they shot the connections with an IR camera, did you personally look at the images?


 
I feel your frustration! How are your 9 conductors routed? Between the tap box and the pecker head are they carefully grouped to minimize inter conductor magnetic effects. BillW.


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## Zog (Apr 15, 2009)

mattsilkwood said:


> About a year ago we installed a big ammonia compressor with a 700hp 480vac motor.
> 
> It has three sets of 500mcm running to it about 75' from the drive.
> The 500s are going to a tap box right above the peckerhead and makeup to 3 sets of 350 DLO cable.
> ...


You do any testing on the motor, cable, or connections? What were the results?


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## John Valdes (May 17, 2007)

The motor shop said it was fine. Call them and ask them if they "*load tested*" it? Very rarely do motor shops "load test" an AC motor. It cost's them alot of money to run that test and it's usually reserved for DC or wound rotor motors. So give them a call or check your itemized invoice as to what exactly was done to the motor.

Next is the drive. Have you been monitoring the current on this drive and motor? I would be monitoring *current*. Heat is the byproduct of current. The drive should be monitoring current along with many other things and you should be able to check the *fault log* and see what faults have occured since the last fault log reset. Check this and let us know. What brand and model number is the drive. I have access to many manufacturers literature and could verify some things with you. Let me know.

You should also contact the technical dept of the drive manufacturer and get some feedback. I would call them right away and get them involved.


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## ElectricArcher (Feb 25, 2010)

I have seen a problem similar to that in the past, it was an issue with harmonic filtering (reflective wave), due to lenght and/or type of wire you have running your motor. You might have to add more or differant type of filter. Thats all I can think of. Good luck!


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## professor poptart (Mar 2, 2010)

wwilson has a good point.
Made sure the cable routing where the cable enters the tap bos and where they are routed between the tap box and the peckerhead is ABC, ABC, ABC, not AAA, BBB, CCC.
Again this should show up as a heating problem. Have you checked with multiple IR scanners?


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## varmit (Apr 19, 2009)

*Inductive heating?*

I would check the conductor grouping(s) to make sure that the correct phases are in the same raceway or metal penetration: If 3 raceways- (1) A, B & C phase conductor per raceway, if (2) raceways- then (2 each) A,B, & C phase conductor in raceway #1 and (1 each) A,B & C phase conductor in raceway #2.
If the conductors are not arraigned in this manner, you will get inductive heating on the wire where it passes through the metal - not at the terminations. 

If this is not the problem, It would seem to be multiple drive problems: 
Monitor each individual phase current, if possible. They should be very close.
If not, i would suspect a malfunctioning control board that is half cycling one phase output. The drive overcurrent limit should catch this. Since the drive is not tripping, this parameter could be set incorrectly, or this portion of the drive logic is not functioning properly.


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## mattsilkwood (Sep 21, 2008)

We have megged all the conductors, to each other and to ground. 
They scaled out. 

I am not for sure what tests they did at the motor shop. They have a very good reputation for big motors in the area.

We haven't done any thermal imaging, just an infared thermometer, but nothing ever stands out as a problem area.

There is three pipes from the drive to the tap box, each one has ABC and a ground. From our tap box to the peckerhead everything is in a 2' long piece of sealtight.

The fault log on the drive has never shown anything odd leading up to an event. Voltage and current are always nice and steady right where they should be. 

We put our recoding meter on yesterday thinking the drives metering system might not be reliable. 

I hope we find something that will shed some light on this.


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