Motors keep burning out

[sfav8r]

Hi,

I am a resi electrician, but a friend of mine has a production facility that utilizes 480v equipment with four motors on each machine. He told me the other day that all 4 of the motors on one machine have burnt out over the past 6 months. The machines (there are two of them) are fed with step up transformers. I have not been there yet and do not have information such as the type of service provided to the building, other than it is 3-phase.

I was going to monitor supply side and load side of the transformers with a logger for a week or so, just to try and at least determine if the problem is supply, load, or the transofrmer itself.

They recently (about 4 months ago) installed the 2nd machine. Most of the motors on the first machine burnt out after that. So I am thinking (guessing really) that they may just be overloading the primary.

Any thoughts or other things to check?

 

[kc8dxx]

Don't Touch that Knob!

Don't Touch that Knob!

Hard to tell sitting over on this side of the WWW, but here is my 2 cents. The last couple times I've seen burned out motors, there were two causes to contend with.

1. Motor Overload Module adjusted too high. The motor overload data sheet will tell you how to adjust the module. For the units we work with, they are to be set to the motor nameplate FLA. The modules include an internal 1.25 multiplier for use with 1.15SF marked motors. Sometimes the infamous "knob twister" will increase the setting when the motor trips out on overload. Or they will set it to 1.25xNameplateFLA without reading the module instructions. Either of these are bad, and can lead to the motor burning out, as the overload is now adjusted too high. The cure to an overload tripping is to figure out why it's tripping, not to readjust the module.

2. Process failed in some manner, leading to excessive motor loading. Deadheading of a hydraulic circuit, dirty filters, lack of lubrication, etc etc all can lead to this. IMHO the machine has developed, over time, some type of motor loading that exceeds the motor rating. Could also be a latent design problem, i.e. some mode of operation that has never been used until now and there's a problem with it. Using the manufacturer's recommended procedures, I would get the machine cleaned up.

We have some customers that just refuse to perform their maintenance procedures. They are basic - stuff like replace dirty filters, periodically have oil tested for contamination, grease bearings, etc etc. I can't stress enough that a Preventative Maintenance (PM) system be put into place to ensure the basic care and feeding of industrial machinery is performed. Of course, PM is an industry in itself. EC&M and Plant Engineering are two trade publications that occasionally feature PM articles.

Good luck. I've worn your friend's shoes (in a manner of speaking), and at times it can be difficult to track down the ultimate cause of motor overloading.

 

[kc8dxx]

PS your idea of checking the power is a good one. Low line voltages can also cause problems with motors.

 

[goskime]

Overloads

Overloads

I worked in a factory where someone installed a 1 hp motor which should have drawn no more than 1 amp. The motor burned up the first night it was installed. Come to find out the overloads for the motor, an electronic overload module had not been adjusted for this motor. The module had a range of overload settings. It should have been set for about 1 amp. It was set for 5 amps. Result burned up motor.

 

[charlie b]

If the problem started when they installed the second machine, and if the problem only occurs on one machine, then it is not likely that the failures are due to low voltage. I say that because the low voltage should be felt by all motors.

Any chance that there are VFDs invovled?

 

[Dnkldorf]

Are we taling about (2) identical machines?

Or is the second one different than the first, with bigger or smaller mototrs and/or controls?

 

[petersonra]

Motor Overload Module adjusted too high. .

While it would have protected the motor if set correctly, finding the reason for the overload is probably more important.

 

[kc8dxx]

While it would have protected the motor if set correctly, finding the reason for the overload is probably more important.

I concur.

Sometimes hitting that EASY button causes more problems that it solves.

 

[Pierre C Belarge]

You say this is supplied from a transformer. I have seen in some instances when a load change ocurs, that the grounding (lack of proper grounding) of the transformer comes to the forefront, whereas before it did not rear its ugly head. So I would also check for the proper grounding of the transformer (x/o) to see if the may be the case of fluxuating voltages.

 

[resistance]

I'm with Charlie b on this one, but the OP hasn't responded??

 

[sfav8r]

If the problem started when they installed the second machine, and if the problem only occurs on one machine, then it is not likely that the failures are due to low voltage. I say that because the low voltage should be felt by all motors.

Any chance that there are VFDs invovled?

My thought was that the newer machine may just not be experiencing the problem yet. It has been taking about 60 days between problems. Also, it is important to note that the SAME motor has not burned out twice. Each of the 4 motors has burned out one time in approx. 6 months. My thought is that if the machine is receiving low voltage (maybe 10%) it is working too hard which caused the motor to burn out early. The new machine which has newer/better motors may just take awhile to experience the same problem...again, just a guess.

I am at a bit of a disadvantage because I haven't been there yet, I just wanted to get some ideas before I go there next week.

I'm also trying the get data on the exact type of equipment this is.

Thanks for the input so far. I'll post anything else I learn.

 

[thinfool]

It is not out of the question that the first machine was furnished with less-than-hi-quality motors. Kind of like using 120v light bulbs vs. 130v light bulbs.

I don't even wanna know the motor mfr., but I have seen some "cost effective" motors fail, after which, the replacements run forever.

 

[hillbilly]

sfav8r...You've got the right idea. Moniter the voltage and current draw of each motor to see if the problem is sustained overload or intermittent fluctuations of motor voltage or amperage draw.

As kc8dxx said, PM of industrial machinery is important. The motors may be operating at near maximum designed HP (load) with the machine in optimum condition.
Any added load caused by improper maintenence (lubrication, or other added friction or malfunction in the moving parts) can cause motor overload.
If I had a machine that was consistently burning up motors and couldn't find a problem with the supply voltage, or obvious problems with the machine itself, I'd increase the motor HP, being sure not to exceed the HP rating of the related mechanical drive.
All of that said, and this is a guess, I'd bet that the new machine has added too much load on the transformer causing decreased motor voltage...It's too small.
Hope this helps.
steve

 

[robbietan]

why not try looking for unbalanced voltage? if these motors are three phase, a defective motor could 'infect' the others through unbalanced voltage.

if this is a mix of single and three phase motrors, you have to check their main panel for unbalance...

hope this helps...

 

[poweringtech]

At 480 volts, This may be a good example of arcing ground fault. Investigate if system grounding is ungrounded. Arcing ground fault for an UNGROUNDED system may cause voltage to go as high as 6 to 8 times. See Industrial Power Systems Handbook by Beeman. Or IEEE Greenbook

If it is ungrounded system, check for single line to ground fault.

 

[e150club]

years ago many years ago... here on long island we had about a dozen german built machines. they had dryers 3ph 240/480 every summer when our 208 dropped off to 198v brown out the heaters would burn up eventualy all changed to newer 220v heaters . ( 208 werent available back then)

 

[brian john]

The writer stated the machines were fed with step up transformers. Are these true step up transformers? Is there only one transformer or more than one, if more than one check the taps to verify all taps are set to provide 480 VAC at the available line voltage.


Look into changing the thermal overloads, these devices (thermal overloads) IMO are ineffective at best. I have tested countless thermal overloads and am not impressed at the level of protection they offer. Ambient affect these devices and as does age as does the aforementioned improperly sized. Try electronics overloads sized very close to FLA.

Check for VFDs and related high level voltage harmonics, check for voltage drop with the motors running, check for proper connections, a low voltage on one phase will adversely affect the running current and motor life. Are the motors sized properly, belts properly adjusted, accumalated dirt and dust, Open or enclosed motors, motor ambient. Line voltage at no load, line voltage at full load, time of day voltage flucuations.

This what I would look at first.

 

[stars13bars2]

The OP is out buying new motors.

 

[sfav8r]

Well, the results are finally in. Some interesting things, but unfortunately, we didn't get all the data we wanted.

We monitored the voltage with a data loggger during machine operation for 1 week. The voltage unbalance factor was excellent, with an average of only .52% and a maximum of .70% (2.8v). No problem there. The total fluctuation in voltage was a low of 392 and a high of 404. These are instantaneous measurements. There wer no periods of sustained low voltages at all. When the lowest readings were logged, they were consistant across all legs.

The disappointing thing is that someone apparently knocked the CT plug loose so we have no PF, load demand, or harmonics!!! :-(

My guess is that this is going to end up being a mechanical issue where an improper adjustment is allowing a given motor to be under too much load. Now that I've had a chance to see the machine, I can see where this could be an issue (It's a surfacing machine for granite slabs).

We are going to monitor for another week with the CTs plugged in and see what we get. I'll post results when we get them.

PS - I guess it's obvious, but I'll state it anyway. My original post stated this was a 480v system, as it turns out, it is a 400v system.

 

[coulter]

50Hz or 60Hz?