4160 Motor Efficiency

[NCDesign]

I am trying to figure out the heat load in a municipal pumping station. The dominating load is three 4160 volt motors, dating from the mid 80's, driving the pumps. I have been trying to determine the standard or baseline efficiencies for motors of this type from this time and can't find diddly squat. Does anyone have information on what the standard or baseline efficiency for these motors might have been? (250 HP, 350 HP, and 1250 HP if it matters) Is there a resource out their that I could use for similar projects in the future?

Thanks in advance

 

[jraef]

Hate to say it, but once you get into MV motors there are no "norms" to reference. Most of them were / are built to spec. So unless you can still get info from the mfr or maybe the original bid spec from the specifying engineer, you are left with a SWAG, or empirical data gathering. If I had to SWAG, it'd be 80% efficiency.

But since that is 80% eff of the connected load, that SWAG is still relatively meaningless without knowing the actual loading. So to do that, you will need measurement anyway. If that's the case, just determine the flow rate, head etc. to determine the necessary work kW requirement, then measure the input kW and the difference is going to almost all be heat rejected into the room one way or another by the motor (a little bit in cables and windage does not translate to rejection into the room, but it's relatively insignificant).

"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

 

[dpc]

I agree with jraef that there is no standard for medium-voltage motors. My guess would be quite a bit higher - probably 90% efficiency rather than 80%. Efficiency could be quite a bit higher than 90%. This assumes something in the 900-1800 rpm range. If these are some slow speed motors, the efficiency could be a lot less. This also assume constant speed induction motors.

The best bet is to contact the motor manufacturer.

David Castor

http://www.cvoes.com

 

[waross]

Agreed. My SWAG would be 80% assuming close to 100% loading. That is a conservative figure for sizing A/C equipment. In practice it may be 90%, but in the absence of hard data, an 80% SWAG should be safe.

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

 

[NCDesign]

You all have pretty much confirmed that without test or factory data it's a shot in the dark. I was glad to see that my initial shot was in-line with your responses. I was pegging it at somewhere between 80-90%. Thanks for all the info.

 

[antigfk]

For a 2, 4, or 6 pole machine I would have thought the efficiency would be above 90%, like 93% or 94%.

 

[LionelHutz]

Larger new 2, 4 or 6 pole motors seem to hit in the 95% efficiency range. I'd guess a 30 year old motor would be around 90%. 80% seems low for just the motor but it could account for the pump too. You need a pump person to comment on the expected pump efficiency and the ratio of radiated heat losses vs heat losses cooled by the water being pumped.

 

[jraef]

Could be 90% at 100% load, but for all we know it's only running at a 50% load. A SWAG is a SWAG. If you are trying to calculate the heat load in a room and you ASS-u-me the heat rejection from the motor is less than it is, you can bury your HVAC system and get in trouble. If you assume the heat rejection is worse than it really ends up being, not a problem.

"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

 

[NCDesign]

jraef, your are dead right a swag is a swag which is why I was attempting to get additional information to set a baseline worst case. Unfortunately there just isn't enough information on the motor to even try and get performance data from a manufacturer. Also, due to the nature of the motor's application there is no way to actually run test it unless a specific set of circuimstances occur, which are out of my control. (The motor, its current installation, and its operation are all out of my control. I would have done things completely different. But that is a topic for another day and a different thread.)
I am consulting on a larger ventilation/cooling problem they have (It is more than these motors although as I stated above they are a big part of it), and based on my previous experience and some of the info from this thread I am defaulting to the motore being 80% efficient at 100% load and not using the higher efficiency numbers. However, on a 1250HP motor the difference between 80% and 90% efficiency is substantial. A 1250 HP motor that is 80% efficient and running at 100% load puts out just over 795 MBH of heat. The same motor at 90% efficieny puts out less than half at just over 353 MBH (using ASHRAE motor heat calcs). You are definitely right that undersizing can bury you, but in this case oversizing can bury you as well. The difference in motor efficiency in this situation is the difference between ~37,000 CFM of ventilation infrastructure and ~74,000 CFM of ventilation infrastructure, assuming you maintain a 10F temperature rise (outside air is 90F and you don't want the space above 100F).

 

[jraef]

Sounds to me like justification for a separate contract to investigate and make the right decision! Fairly decent ROI if the efficiency is higher than what is SWAGGable (making up a new word here) in my opinion. I'd pay for that if it were my system.

"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

 

[LionelHutz]

My guess would be that it's in the customers best interest to replace the high run-time motors if they are truely 80% efficient.

I don't recall seeing any large motors where the efficiency changed by more than a few percentage from 50% to 100% load.

Sounds like more investigation is necessary. I'm not surprized. I had an idea you'd find that being overly conservative would also have consequences but didn't bother posting it last time (it wasn't the question being asked).

 

[electricpete]

NCDesign - you would know better than us... is it possible to build capability for easy future capacity increase into you hvac design? Perhaps they can bring it on-line in winter and then study it and accomplish any further required uprates before summer? With that kind of approach as a backstop, you could be more bold in targeting a realistic number instead of guarding against the worst case unknown.

Sorry, I have at the moment nothing to contribute to your original question.. has been covered well.

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[electricpete]

All of our plant original motors were built in the early 1980’s. We have about 12 different families of 4kv motors. I was able to easily find 6 of the oem data sheets, with efficiency info summarized below fwiw:

Hermetic chiller motor 600hp 4kv, 3550rpm.
Efficiency at 50%/75%/100%: 0.956 / 0.952 / 0.938

Vertical Motor 1000hp, 4kv ~3600rpm
Efficiency at 50%/75%/100%: 0.943 / 0.949 / 0.949

Vertical Motor 400hp 4kv, 1800rpm
Efficiency at 50%/75%/100%: 0.92.8 / 0.93.4 / 0.931

Horizontal Motor 800hp, 4kv, 3561 RPM
Efficiency at 50%/75%/100%: 0.940 / 0.948 / 0.949

Horizontal Motor 600hp, 4kv, ~3600 RPM
Efficiency at 50%/75%/100%: 0.927 / 0.937 / 0.934

Horizontal Motor 800hp 4kv ~1800rpm
Efficiency at 50%/75%/100%: 0.933 / 0.927/Unk (not recorded at full load).

Regarding copper magnet wire conductivity, NEMA Standard MW1000 (Magnet Wire) 1981 version said the same thing as NEMA Standard MW1000 2010 version says: 100% of IACS as a minimum. I don’t think there is much variation in that except a few very special applications that might go higher. There are plenty of sources of efficiency variation among older motors, but as far as I know the conductivity of stator winding copper material is not one of them.


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[electricpete]

By the way, all motors except the first are open construction, either ODP or WP2.

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