3 phase motor test. 6

[rockytee]

I am a self employed residential and light industrial repairman. I don't get many calls on 3 phase stuff but have recently with the addition of a new customer. He is a propane dealer and has several 3phase applications for his pump motors. I am about to check on a job this morning and was wondering what would be the best route in diagnosing his problem.
PROBLEM: 1 to 1.5 hp seald elctric motor.240 three phase. The pump is tripping the reset switch. ( this what I was told I haven't gotten to the site yet to determine if "reset" switch means motor temp overload switch or breaker switch.)I was wanying to know the steps I should take in determining if the motor is bad or ineffecient voltage or faulty "reset" switch.
I am about to leave to go check on it so I doubt I will get a reply before I leave But I would like to see if I checked everything right, when I get back. I will also have alot more details on the specifics of the situation.
P.S. I did ask him if this was a new install and he replied that it was a fairly new customer but he did reuse a pump and motor from another account and that the pump did have some age on it.
Love the site and really appreciate the replies that I have read on other posts. Thanks for your help.
Sincerely Rockytee.

 

[edison123]

It is probably motor overload protection.

Confirm the motor rated voltage (on the name-plate) matches the supply voltage (through a voltmeter/multimeter). If it doesn't, then the motor is unfit to run at that supply voltage.

Check the running current against the rated motor current. If it is high, probably, motor and pump are mismatched.



*Why make the same mistake twice when there so many new ones available*

 

[waross]

Depending on how fast the motor trips, you may want to check winding continuity and megger the windings to ground. What is a good megger reading, what is an acceptable reading, what is a bad reading?
Megohms is good. Over 50,000 to 100,000 ohms is acceptable.
Less than that, use ohms law to determine the leakage current and use some common sense to decide if this is enough currrent to cause your problems.
Use voltage to ground, 120 volts on 120/208 volt systems.
No megger, use a light bulb and 120 volts to ring to ground. It's better than nothing and better than a multi meter for insulation resistance.
respectfully

 

[ScottyUK]

Just one additional thought: you mention propane which is obviously a flammable gas. Electrical equipment designed for use on and in the vicinity of equipment usign flammable gas is governed by a fairly onerous set of regulations. In Europe it is the DSEAR and ATEX legislation. If you see wording along the lines of (e.g.) Class 1 Div 1 or EEx D IIB T4 on the equipment then ideally get help from someone who is trained to work on hazardous area apparatus.


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Sometimes I only open my mouth to swap feet...

 

[rockytee]

Thanks Guys. I really appreciate the help. It was a 3 hp sealed motor and yep it was class 3 Scotty. It was wired for low volt 230 with possible high volt 460. I checked amp readings on all three legs and got 9-10-11 amp readings (respectively) The motor was rated at 8.1 amps, wired low volt. Line in readings were dead on 230 across any 2 legs and 121 - 123 volts to ground. There fore leading me to believe the relief vavle is malfunctioning or adjusted too tight.I'm going to plumb in a guage to find out what pressure it is running at. If I run the fill hose back into the tank w/ valve wide open the motor will run forever holding 5 to 6 amps as the load is increased (closing fill valve) the amps rise to well over rated 8.1 The pump is quite old and one of the employees told me it had been under water on several different occasions. I also believe the windings may be bleeding over or brushes getting thin not putting enough contact pressure on armature.
The connection box on the side of the motor was very rusty and the wires were coroded very badly. I wire brushed and cleaned them as well as I could and put new wire nuts on to help continuity. No change.I don't have a megger really not sure what that is. Well I'll check back tomorrow and let you guys know what else I've found out and see what new advice yall have. Thanks again hope yall had a great weekend.

 

[ScottyUK]

I doubt there would be any brushes or an armature for you to worry about. It's almost certainly a standard 3-phase squirrel cage induction motor. Sounds like you are on the right track with overloading of the motor. Good luck.


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Sometimes I only open my mouth to swap feet...

 

[waross]

Another possibility is that the pump has been changed to a larger size (displacement) than the motor is intended for.
respectfully

 

[edison123]

rockytee

1. Check direction of rotation

2. Check the set-point of the trip (is it an mcb ?)



*Why make the same mistake twice when there so many new ones available*

 

[controlsdude]

I work in conveyor and see 3 phase motor faults all the time.

1st
Do you have a mechanical problem? How would you determine this with a pump?

If it is a pump, the pressure has to build for it to be a mechanical issue therefore the pump motor will trip some time after in most cases. Check all the valves for proper settings.

2nd
99% of the time when I have a 3 phase motor fault, the motor is usually single phasing. Check the 3 phase connection, motor contactor, overload, and at the pecker head at the pump. Is it a VFD? If so, check the parameters that have been changed and do they match the motor nameplate data? Any instantanous trip is usually loose wiring.

 

[jraef]

If your load is INCREASING as you close the valve, then it is likely that you have a "positive displacement" pump. That would be typical of a fuel transfer pump, it is likely a rotary gear pump or a vane pump. This would mean that your instincts were correct, you have something wrong with the valve. If it were a "cetrifugal" pump, load would only increase when there is MORE flow, not less.

JRaef.com
"Engineers like to solve problems. If there are no problems handily available, they will create their own problems." Scott Adams
For the best use of Eng-Tips, please click here -> faq731-376

 

[powerjunx]

rocketty, i agree with scotty. I'm pretty sure its only a simple 3 phase squirrel cage motor. Better discard the idea of brushes and armature where it is impractical to use such machine in propane rich environment.

 

[rockytee]

Well I don't know if the company will actually bench test the motor or not,but the customer (on my recomendation)(hope it was right)decided to send it to a motor shop in Franklin, Tn.
I suggested plumbing in a guage to see how and how much pressure was building. Once I told him My estimate of time of trouble shooting and parts to do so, then actually replacing it with a new one or repairing the relief vavle he decided to have it rebuilt.
When it comes back if the problem was windings then all will be well if not then it will be overload protection or vave problems
I would like to thank everyone for your help. Thanks, Rocky

 

[berkley]

insulation resistance test. case study-3 phase motor

 

[powerjunx]

rockytee, i encountered newly built motor i'd spent alot of troubleshooting, diagnostic test, re-calculation of pressure heads, pump sizing, etc. But the latter,I suggested to replace a new spare motor with same specification and brand it's runs smoothly, hence, i'd found out that the installed new motor is the culprit.
Then, i later ask some experts of how OEM performed bench test of newly built machine. One said; "since plenty of machine were manufactured in a row, a random testing were made. Thus, there would be a chance of having a defective products on a certaing population or batch." Quite real??
Make a consideration about the machine itself.





"Whenever you are asked if you can do a job, tell them, certainly I can! Then get busy and find out how to do it." Theodore Roosevelt.

 

[itsmoked]

Hi rocktee:

Having current readings over the FLA is a sure sign of overloading. All your readings being consistent sounds good. In most of these cases I almost always find the system to be the problem, not the motor or pump.

Your inprompto test was an excellent idea. It further points to the system as having some restriction. Possibly a filter or if no filter, debris in a line, or valve, or orifice, or seat. I would pursue that angle. A gauge is a 'must' as it is one of the few windows into the system.

Once you have a gauge in you can hopefully load the system down with your bypass valve until the FLA is reached. Mark this point and everywhere further upscale with a [red]RED[/red] sharpie so the customer knows when their filter or, methods are going to toast the motor.

Keith Cress
Flamin Systems, Inc.-

http://www.flaminsystems.com

 

[rockytee]

Well we have sent the motor off and had it tested and "tuned". They claim they could'nt find anything wrong. My customers employees say they checked the pressures and the by-pass is working properly. (last time I was there I could'nt find any marks on any of the plugs; ie. from having had a wrench of some kind put on them) HUMMMMMM.But anyway the customer is still having the trip-out problem. I was looking at it again the other day and the motor control is in one box and the fuses are in the box before it(DUH) but I did notice the brass on one end of one of the fuses(on the load side) was dark. You know the color non ferous metals turn when they get toooo hot. So I believe I'm gonna slipp by there with a few new fuses and try that. I have a friend of mine who is a commercial electrician said that he has seen on one other ocassion where a fuse blew but left enough residual burnt metal to test on a voltage and contiuity test but not enough to carry a work load.
I would like to thoroughly thank everybody for your valuable in-put. I hope I sent the thank-you to everbody. If not, I appologize. I stay soo busy I don't get much time on the computer to keep up on a regular basis. Again I thank you. I'm sure glad to be a member of Eng. Tips.
Greatfully, Rockytee

 

[itsmoked]

Flaky fuse holders are pretty common. You may be on to something there. Keep us posted!

Keith Cress
Flamin Systems, Inc.-

http://www.flaminsystems.com

 

[bfhamr]

Were the voltage readings taken while the pump was running under load? If not it might be a good idea to check it. I've seen a couple instances where the wiring was too small for the size motor being run.

Dan

 

[rockytee]

Thanks again guys. I have'nt gotten back out there yet to try the new fuses. I did test the voltages under load. I don't recall excatly what they were but it was 5 to 10 volts dop at start up and an imeadiately back up to normal. That's normal on start up right???

 

[jraef]

For a 1-1/2HP pump motor, you should not be seeing that much of a voltage drop. It's looking more and more like the flaky fuse holders or under sized wire issue the more you disclose. Could also be a connection that has worked loose over time and/or become corroded, a pin-hole in a motor lead wire that is giving you a high resistance ground fault, any number of circuit related mishaps. I'd rent a good crank megger (if you don't own one) and have at it!