Cost of losses in a motor

[rockman7892]

I was reading an interesting article about the use of High Temperature Superconducting material used in motor as opposed to the commonly used copper. The article went onto talk about the operating cost savings of the motor due to the decrease in losses that are seen with copper wound motors.

The article stated that a 5,000hp motor operated run 24hrs/day 7 days a week would have a savings of $50,000/year as a result of lessened losses due to copper.

I found this cost savings statement to be interesting, for I never realized that the losses associated with operating larger motors cost that much. I know this cost is dependent on a number of motor variables, but overall for larger motors above 1,000 hp is there that much of a cost associated with electrical losses in a motor run constantly throughout the year? Does the number stated in the article of about $50,000 per year seem right?

 

[TurbineGen]

It just might be correct, depending on the efficiency improvement and the cost of electricity.

5000 hp ~ 3000 kw
3000*24 = 72000 kwh/dy
72000*365 = 26280000 kWh/yr
@ $.08/kWh = $2,102,400 running cost
Now with a 1% improvement in efficiency - 2102400*.01 = $21,024 savings annually.

If they could make a motor 2% more efficient and the cost of electricity is $0.12/kWh then $50,000/year savings might be possible. Mind you, we are talking about a 3MW motor.



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

 

[Unotec]

First, what is "high temperature super conductor". The highest temperature superconductors I am aware of, work in temperatures as high as liquid nitrogen's

<<A good friend will bail you out of jail, but a true friend
will be sitting beside you saying ” Damn that was fun!” - Unknown>>

 

[dpc]

Theoretically, superconducting motors and generators could save a lot of energy by reducing copper losses to essentially zero. It's a long way from showing up at your plant though.

Even though induction motors are pretty efficient, motor losses are a sizable portion of all energy losses in industrialized countries. So they are a favorite target for anyone with the next great idea.

 

[rockman7892]

As dpc said the article stated that these motors are indeed a long way away from industrial/commercial applications mainly because of cost. The majority of the up front cost was due to the cooling system that was needed to keep liquid nitrogen or whatever else was being used to cool the superconductors.

I found the article interesting because I never really realized how much money was associate with losses. I know effeciency is made up of both electrical and mechanical losses and the electrical losses are mostly in the form of heat from the resistance of the windings. It made me begin to wonder if there was anything that can be done on existing copper motors to reduce the electrical losses. I know the mechanical losses are probably more easy to decrease however I was just trying to think outside the box to see if there is any way to reduce electrical losses in some of our larger motors.

 

[itsmoked]

They never seem to go too far into how much it costs to keep something the size of a large refrigerator in ambient space at minus 200F. Probably cost oh.. $50k/year.

Keith Cress
kcress -

http://www.flaminsystems.com

 

[jraef]

I'm not so sure about those figures, the number could easily be higher.

From a course on improving motor efficiency I took a few years ago sponsored by EPRI;

Breakdown of motor losses as a percentage of total losses:

Stator copper losses (35%), based on the number of stator slots and the cross sectional area of the winding conductors.

Rotor copper losses (25%), based on the cross sectional area of the rotor bars and the joint between the bars and the end ring.

Core losses (25%) from hysteresis and eddy currents in the lamentations, also affected by air gap and core length.

Windage and bearing losses (5%), based on frame design and cooling needs, plus bearing designs as well as manufacturing tolerances.

The last 10% of losses are stray load losses caused by leakage flux induced by load current fluctuations. These vary as the square of the load.

So of all those, if you could somehow use the not-yet-existent super conductor in both the stator and rotor, you could reduce a percentage of 60% of the losses. Lets say we pick a 5000HP (3730kW) high efficiency motor that is 95% efficient (not unheard of). That means the total losses are 186.5kW, of which 111.9kW are from copper losses. If you manage to cut that by only 80%, you save 89.5kW, for 8760 hours/year, so that comes to about 784,195kWH/yr. At $0.12/kWH, that comes to about $94,000.00... sweet!

I won't hold my breath though...


"If I had eight hours to chop down a tree, I'd spend six sharpening my axe." -- Abraham Lincoln
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[waross]

Windage is admittedly very small but consider;
With super conductors you won't need fans to cool the motor. Actually air flow across the windings would be counter productive. The super conductors would work better in a vacuum. Windage losses will probably be replaced by the expense of running a vacuum pump.

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

 

[LionelHutz]

Jeff,

I agree with the stator losses, I would expect 2-3% savings there.

Not so sure you can use superconductors in the rotor. Doesn't the rotor require some resistance to create the starting torque and not draw a huge locked rotor current? If I'm thinking about that right, you'd have to use a VFD to start the motor which would negate the savings if it was run continuously. Of course, it could be bypassed once running.

 

[waross]

The rotor current is also limited by the inductive inductive reactance of both the rotor and the stator. This may be increased by placing the rotor bars deeper in the rotor. But, your comments point out that simply cooling the windings will not be the only design hurdle facing the development of super conductor motors.

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

 

[jraef]

Good point Lionel, I was thinking only of the challenge of somehow pouring this magic elixir into the rotor slots and then somehow forming it into an end ring, forgot about how the rotor functions in the first place. Maybe that's why they hedged their bets on the efficiency claims ;-)


"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

 

[TurbineGen]

I'm curious why few people here have addressed the stator iron loss issue. 35% due to iron. By cutting the iron laminations half as thick, doesn't that reduce the loss by a factor of 4? This seems like it would be easier done than using a superconductor and attempting to keep the machine cold. Does that sound about right, or am I missing something?

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

 

[dpc]

Core losses have been reduced quite a bit over the last 100 years. The special steel used and the very thin laminations already used have reduced the losses to the point where further improvements come at a high cost. If there was a cost-effective way of reducing iron losses further, someone would be doing it. There has been a lot of money spent (and wasted) on working to improve motor efficiency.

 

[itsmoked]

Sounds like the eddy current loses are going to add to the refrigeration costs over what the ambient will cost.

Keith Cress
kcress -

http://www.flaminsystems.com

 

[MotorVib]

Just as a side note if the lam steel gets to thin there are problems with handeling Lam that make up the rotor and the stator. It is like glass because of the large grains size that comes from anneling the steel.

Chris

"In this house, we obey the laws of thermodynamics." Homer Simpson