Motor efficiency degradation over time??

[SeattleLuke]

Hello all,
I'm doing an energy cost analysis for a hatchery that uses multiple large (100-150 hp) pumps for the process flows. My question is this:

Can anyone tell me how much the efficiency of a motor decreases over time? These motors were installed in 1972. I figure the pump efficiency has dropped off quite significantly but I'm wondering about the motors as well.

2%...5%...???

Thanks,
Luke

 

[electricpete]

For sure the efficiency of a motor you buy today is likely higher than one you bought in 1992 due to differences in design.

I presume you are asking about aging mechanisms. Here's my guess from largest likely changes:
1 - if the motor has been rewound during the period, then improper stripping of the windings at too-high temperature can damage the core interlaminaro insulation and increase core losses.
2 - If large ODP motor with filters and you haven't been changing the filters - temeprature will go up which increases I^2*R losses. Also very e2xcess dirt which blocks internal cooling passages of ODP motor.
3- Bearing packed full of grease may run hotter and less efficient. Bearing exposed to higher force from unbalance or misalignment may run hotter.
4 - Various non-ideal conditions such as unbalance and misalignment can lead to vibration which perhaps can decrease efficiency. But vibration shouldn't cost much energy by theory - it is exchange of energy between mass and spring stored energy without much energy dissipation, with energy loss only thru damping mechanisms.

=====================================
Eng-tips forums: The best place on the web for engineering discussions.

 

[electricpete]

Should've said from likely largest changes (1) through smallest changes (4).

=====================================
Eng-tips forums: The best place on the web for engineering discussions.

 

[SeattleLuke]

Thanks electricpete,
I was hoping to get an idea about how much the motor efficiency might fall off. I was hoping someone has read a whitepaper or other article stating that a motor will lose such and such efficiency per year...

I know there are a lot of factors that could degrade the efficiency, but a range would be good.

-Luke

 

[electricpete]

The biggest effect cited above (core losses and other changes during rewind) is well documented:

http://www.easa.com/indus/rwstdy1203.pdf

The other changes are very small - no studies I know of although you might start with google. But again I don't think you'll find much there.


=====================================
Eng-tips forums: The best place on the web for engineering discussions.

 

[edison123]

The motor efficiency does not fall because of aging.

As for efficiency loss during rewinds, as a motor rewinder, I disagree with epete (may be for the first time). There are methods to strip windings without heating core. So the iron loss does not increase after rewind. On the other hand, we have the opportunity to use newer and better insulation for older motors rewinds, which almost gives leeway to pack more copper area thus leading to lower copper loss and higher efficiency.

Muthu

http://www.edison.co.in

 

[TurbineGen]

Just because a motor is old doesn't mean it is any less efficient now than it was 10 years ago. In the case the motor was rewound perhaps the efficiency changed slightly, but this is usually not that much unless the motor was modified to increase performance.


The really is no degradation curve such that you are looking for. Outside of physical damage and rewinding of the motors, the efficiency should remain mostly unchanged through out the motor's lifetime.

------------------------------------------------------------------------
If it is broken, fix it. If it isn't broken, I'll soon fix that.

 

[electricpete]

Muthu - I think what you said it consistent with what I said. I said "improper stripping of the windings at too-high temperature can damage the core interlaminaro insulation and increase core losses." which certainly does not preclude the possibility that it can be done properly (lower temperautre) to avoid degradation.

Good point that there is opportunity for improvements during rewind - for example newer insulation materials can allow more room for copper.

I also agree TurbineGen - we don't generally expect aging to cause any significant degradation in efficiency under identical conditions and the items I mentioned (other than improper stripping during rewind) will have very small effects - just listing the areas for consideration.

=====================================
Eng-tips forums: The best place on the web for engineering discussions.

 

[waross]

The irons used in transformer and motor laminations for the last eighty or so years do not degrade as earlier irons did.
Not much changes with time in a motor. I suspect that the major cause of efficiency drop, when there is one, would be dirt and/or corrosion impeding the proper flow of cooling air. This is generally correctable.

Bill
--------------------
"Why not the best?"
Jimmy Carter

 

[SeattleLuke]

thanks for the repsonses everyone. For my cost analysis I'll just assume that the motor efficiciency has not changed. This will be the more conservative approach anyway.

Thanks again!
-Luke

 

[jraef]

What if the insulation has degraded, but not enough to cause a protective device to take it off line? Current leaking to ground or phase-to-phase is not doing anything useful...

By the way guys, he said 1972, not 1992. Those motors are almost 40 years old. The difference in efficiency compared to a new design would be dramatic.


"If I had eight hours to chop down a tree, I'd spend six sharpening my axe." -- Abraham Lincoln
For the best use of Eng-Tips, please click here -> faq731-376

 

[electricpete]

The categories of losses tabulated for non-vfd motors are typically: I^2*R, Core losses, friction/windage, and stray. The reason insulation losses are not listed are because they are very small in comparison. You can estimate them from Doble test results.

You're right - 1992 was a typo.

=====================================
Eng-tips forums: The best place on the web for engineering discussions.

 

[edison123]

pete - then no disagreement at all. phew.

Muthu

http://www.edison.co.in

 

[electricpete]

LOL. I wouldn't use me as a benchmark for correctness. But when it has to do with motor repair, I certainly feel better when my comments agree with yours. It's good we have a lot of motor repair shop guys here on the forum: Muthu (edison), Ray (rhatcher), Sean McGrady (others?). Maybe someday we'll have enough for a motor repair forum.

=====================================
Eng-tips forums: The best place on the web for engineering discussions.

 

[SeattleLuke]

Excellent comments! I'm going to assume that the motor hasn't lost any efficiency. Back when the motors were installed in 1972 I think they were about 90% efficient. I'll just keep this value. Although I could just as easily enter 85% in my excel sheet and see what happens...uh oh...can of worms...

 

[IIEE2]

0 % , if is properly maintain... it will run with same efficiency as it is before ,, proper maintenance cost very little!!!..

 

[edison123]

Thanks pete for letting me know other winder guys.

Hi Ray & Sean.

And we want a motor repair forum pronto, or else, .....

we will filibuster (though Ray & I have already agreed to disagree recently).

Muthu

http://www.edison.co.in

 

[waross]

I rather hope the winder guys stay here. A lot of the motor issues benefit greatly from the input of the winding experts.

Bill
--------------------
"Why not the best?"
Jimmy Carter