3-Phase Squrrel Cage Well Pump Motors

[AgEng02]

I'm a recent graduate and I specify well pump motors in new water plants along with replacements after they fail. My company in past few years is having numerous problems with the well motors failing within 5 years, while in the past the motors could last up to 25 years. The motors are used are in the Greater Houston, Texas Area, so the coastal environment is harsh along with Houston's pollution. I'm looking for the best quality at the best price in motors. I'm looking for information on motor manufacturers, heat rise, insulations, enclosures, monitors, heaters, starters, and cost. Any info will be helpful.

Greg

 

[AgEng02]

In addition to the information I posted, I'm looking at a typical 300HP 3-phase, squirrel cage induction motors. My motors range from 1/4HP-350HP.

 

[electricpete]

I am in the Houston area also except closer to the coast.

I would say if you want a reliable motor in general you will that you will find some very good off-the-shelf options among the IEEE841 "severe-duty" motors.

Other parts of the reliability picture are of course careful review of application requirements, consideration of preventive maintenance, condition monitoring, post-mortem examinations. Part of condition monitoring is the process of verifying your assumed application parameters during actual operation. (loading, voltage, starting duty).

 

[acmotorengineer]

I agree with electicpete, an IEEE 841 motor is pretty rugged.

are you looking for vertical or horizontal motors?

also what type of failures do you have?

 

[AgEng02]

I appreciate your comments. They've been helpful.

We use vertical motors. The motors usually fail from insulation breakdown. We used to spec WP1 enclosures and Insulife 2000 insulation with US Motors (two dips and bakes). For the past few motors I have been going to TEFC thinking that will help. I'm also wondering if I should go to a the Insulife VPI 2000 (two cycles of vacuum pressure impregnation). Any thoughts on that?

 

[AgEng02]

Anybody know what a typical 300HP IEEE 841 motor costs?

 

[BJC]

Check how much work the pump is actually doing. They can be overloaded. If the water table drops or a discharge valve is wide open you could be overloading the motor. Check the pump curves.
Are you using hollow shaft motors?

 

[CB2]

I'm not sure, but I don't think the two or three manufacturers of vertical hollow or solid shaft high thrust motors would build an IEEE841 in the size range (NEMA) AgEng02 is using.

A good EASA motor repair shop should be giving you more information than you have given us. What do they say about your failurers?

 

[AgEng02]

I apologize for the lack of information, but I am the only electrical engineer in the company. This info was passed down to me from civil engineers and most of this was handled by other firms in the past. I have been told that the motor repair shops say that the cause is lightning surges. We started installing Multilins and the data shows the breaker trips and surges are at start up. I was told this was due to insulation breakdown caused by water and excessive heat. They also found rust inside the WP1 enclosures.

Concerning the motor shafts, I don't know what we've used in the past. Our specs dont say anything about shaft types. I did look at a recent installation and it was a hollow shaft motor.

 

[busbar]

If the pump electrical system is ungrounded/“floating” in the 240-600V range, some small transformers and a resistor to permit high-resistance grounding may be more effective than non-linear “TVSS” devices like MOVs or SADs for limiting insulation-damaging phase-to-ground transient overvoltages.

Search this site for “high-resistance grounding”.

 

[CB2]

If lightning strikes are taking out your motors the Multilin will record this by letting out some smoke. Do you have lightning surge suppressors in your starters?

For the moisture issue in the motor, do you install winding space heaters in the motors? What is your duty cycle, run time/off time? Are the motors in direct sun light? What are the running loads of the motors that have failed?

If you decide that heat is the issue, I would suggest you intall motor winding RTDs in the next motor purchased or rewound. Connect them to the Multilin and monitor.

Would you circumstances be something like:
The well pump is started in the morning to meet peak demand, which is at or near full load (or better yet in the service factor because the mechanical side of the house wants to save capital costs), operated all day on a hot day (typical of Houston 100+) and the motor is in full direct sun light(adds 20 degrees to operating temp). Runs through the evening peak and is shutdown for the night, motor cools down to ambient and sucks in the moisture (lots of that in Houston). Add to all this the lightning strike related power problems (seen that in Houston), five years seems about right!

 

[electricpete]

I'm not sure if IEEE841 would be available as pointed out. Also TEFC would also be better than ODP. If ODP, WPII is slightly better than WPI. Those apply to the IC rating. Also you can specify the degree of ingress protection IP rating.

IHMO there is no doubt that global vpi is superior for outdoor applications. Also I have a preference for epoxy over polyester I know some will disagree with that based on recent advances.

"Insulife" sounds vendor specific.... not sure what it means. A lot of the OEM's can provide info on their systems. Some will brag that their insulations systems have passed immersion tests and are used in hermitically-sealed motors immersed in refrigerant. I would look for this as well as an insulation system that has been around for awhile (time-proven).

As mentioned space heaters are an important acccessory. Should be set up to come on automaticlly when motor is switched off.

 

[busbar]

There also heater gizmos that use low-level off-cycle DC current applied to stator windings, like:

http://www.motortronics.com/products/otpr.html

http://www.ab.com/manuals/pd/1410-2.2.pdf

http://www.benshaw.com/literature/applications/AN0009.pdf

{part of a SS starter}

http://www.emersonct.com/pdProducts/downloads/appNotesPDF/CTAN194.pdf

{VF drive software implementation}

http://www.usmotors.com/Products/ProFacts/1-109.htm

{electromechanical method}

http://www.friesenelectric.com/brochures/pdf/Motor_Control/S_Motor_Winding_Heater_1pg.pdf

http://www.dnhindustries.com/

 

[don01]

ageng02
the stuff the crew have pointed out sounds like the go. But as a back up find out what changes where made at the time the first of these failures was installed or about the time of the failures. As I read your post I am starting to feel there is a root cause here. And the techinical may fix it but finding the root may be suprising.
(with lots of repect to the prior posts)

Regards
Don

 

[don01]

ps
re lightning strikes,
I dare say Houston has been getting lightning strikes for many years, Has the power co changed the way they work or the regs around that area changed ?

Do all the failed units have rust in WP1 enclosure? (what is WP1 enclosure?)

Are these at various sites around the region or one plant site?

Don

 

[GusD]

Hello AGEng02

Interesting that someone told you that the old motors lasted 25 years and the newer motors only last 5 years.
Something very drastic had to happen to the systems to account for the 500 % reduction in durability.
You might have to ask yourself what really changed either on the new motors or on the electrical systems(protections).
The previous advice to make sure your Anti-cond heaters are working is a must.Loads of water can accumulate in the windings if you don't have heaters.Houston polution and all.If your motors are randonm wound ,the VPI may not make much difference.
Lets assume this scenario.Years ago the demands were probably lower so the motors ran at low loads,low winding heat.In the last few years the demand increased and motors are now running at full tilt or more, and pretty hot as well.For every 10Deg increase in operating temperature
you reduce the life of your motor by a half.
Next time ,when a motor fails,follow it to the repair shop and look at what the windings look like.Ask the shop to give you their opinion on the failure.
If the windings are toasted ,you could bet you have overloads and consequent overheating.If it burns on aturn to turn short it can be poor winding or poor impregnation.
If it shorted to ground,the water accumulation could be the culprit.
Make sure you have Anti-cond heaters, also for a few dollars more install winding RTDs.

Good luck

heatThere is one possibility. previous adv lchange for this

GusD

 

[electricpete]

Good comments Gus. I will offer one comment... VPI can make a tremendous difference in environmental protection even for random wound. The proper technique would include half-lapped layer of taping of the end-turns which ends just inside the slot and overlaps with slot liner/wedge/separator/fillers for form a continuous resin retention envelope. It is a technique specified for some nuclear safety-related harsh environemtn motors.

Maybe instead of specifying the materials/technique etc I should have suggested to specify the performance requirements. NEMA MG-1 has provisions for a sealed winding conformance test which includes complete immersion in liquid, followed by an overpotential test. You can either ask for the test or just ask the OEM to provide documentation that his insulation system has passed the test on comparable motors. Talk to some good distributors and I'm sure they can pitch you some good product lines for your application.

 

[GusD]

Correct electropete.

If the end turns are taped as you mention ,than VPI may be of some value.AgEng02 mentions that this motors operate on an environment that is near the sea and subject to possible excess polution.This is not a Tropical climate but conditions could be similar and subject windings to the same problems.The windings could be treated with a Fungicidal Treatment.This coumpound can be added to air dry varnish to discourage the growth of fungus.
Like many other problems,one cannot find the right soulutions unless you know what the problem is.
My suggestion for AnEng02 to follow that motor to the repair shop and find out what failed and how,may give you surprising results.


GusD

 

[Steventyj]

I would find out all of the nameplate information on some of the motors that had service lifes of 20 years +. Maybe someone decided to buy motors with a SF of 1.0 instead of 1.15 etc.. I would also take current draw readings of the new motors when they are full load to check if a re-evaluation of the application is neccecary. Much simpler than earlier suggestions but I'm new as well.

 

[powertronc]

I recommend you talk to the manufacturer of the 300HP motor. They should have the background, knowledge and test equipment to identify the reason for these motors only lasting five years. If they can't help you or won't help you then you really should be concentrating on finding a new motor supplier. I should also point out that designing a motor for the operating environment you described in your posting is not something every motor manufacturer can do.