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Member

Join Date: Apr 2008
Posts: 5

Electrical engineering

06/10/2008 7:44 PM

Can we use chiller to cool the air which is being used to cool the motor winding instead of heat exchanger. The system is now with heat exchanger for the cooling of 2500 KW DC motor of a Hot rolling Mill

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Power-User

Join Date: Jan 2008
Location: Silvis, IL (Quad Cities)
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#1

Re: Electrical engineering

06/10/2008 11:42 PM

It should be possible. Just make sure that you keep the humidity down inside the motor and make sure that they have approximately the same amount of cooling.

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#2
In reply to #1

Re: Electrical engineering

06/11/2008 1:13 AM

dear sir,

that means you require a dehumidifying plant with auto humidity control. Thank you

Regards,

Unni

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#3
In reply to #2

Re: Electrical engineering

06/11/2008 5:45 AM

Maybe, maybe not. I should have said that you want to keep the temperature inside the motor above the point where condensation would form. Would a dehumidifier work? Yes, but it would probably be more expensive than what you are wanting to spend. Basically what I meant was don't go overboard with the cooling. I just didn't have the right words last night.

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Power-User

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#4
In reply to #3

Re: Electrical engineering

06/12/2008 12:23 AM

It will work and you cna try and see the results

shivaram

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Commentator

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#5

Re: Electrical engineering

06/12/2008 1:01 AM

Chiller will consume additional power and maintenance cost. Secondly when you chill the air the ,it can get saturated and may lead to water droplets coming out of air if humidity is high. Such fine liquid droplets can cause abrasion. Thirdly the motor must have been designed to run at higher temperature.

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#6

Re: Electrical engineering

06/12/2008 3:07 AM

The short answer is no. Chiller produces chilled water, and chilled water can only be used via a "water to air heat exchanger" to cool the air stream.

However, there are some direct expansion air cooled packaged systems like so called rooftop air cooled units where you can have the air sucked in and cooled down and distirbuted to the target cooling spot. But, these have limited capacities (upto 1,000 MBH) and they are not as energy efficient as Water Cooled Chillers. Their efficiencies are comparable to systems containing air cooled chillers though.

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Power-User

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#7

Re: Electrical engineering

06/12/2008 4:14 AM

Why don't you check with motor manufacturer as I am sure machinery manufacturer must have used it after confirmation for designed intended use.

More so, using chilled water plant to cool the air - to cool the motor, seems like too much of a possible maintenance risk.

My advise, Keep it simple.

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#8
In reply to #7

Re: Electrical engineering

06/12/2008 10:57 AM

Absolutely.

Keep this in mind: the inefficiency =(1 - eff.) of the motor is lost due to friction and magnetic losses. This is manifest as heat, and is why motors get hot. This continuous addition of heat to the motor's mass will help ensure that no condensate forms inside your windings. But don't count on this value alone for your sizing or you'll have difficulty. This seems to push the solution towards a variable air volume delivered to the motor to handle a wide range of load conditions.

Size your chiller according to the equation BTU=1.08 x CFM x deltaT where the BTU value is equal to the inefficiency plus any heat gained from convection (if it's hot around your motor due to process or your geographic location) plus direct radiant gain from the hot roll process if the motor is in line of sight of any surfaces that are 100°F or more above desired motor temp. The delta T is the difference between chiller discharge temp and the desired temp of the motor.

Run the discharge air from the chiller through a dessicant-type air dryer to drive the dew point below 0°F (-40 & -90°F are typical industry std discharge dew point values, and first look to heatless regenerating types). The chilled air must be run through a coalescing filter to sequester all the moisture possible before entering the dryer.

Last safety I would put on the system would be a temperature controller that will look at two variables: outside air dew point, and motor temperature. The controller should shut off or throttle way back (depending on heat generated around the motor and its usage. i.e. is is on 24 hrs - 7 days, then throttle the air flow, don't shut it off!) on the air supplied to the motor. If the motor temperature is getting within 10°F of Dew Point, start reducing the volume of air delivered. If you get within 5°F, then shut off air flow as a final safety measure and you should be fine.

Hope this helps.

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#9

Re: Electrical engineering

06/12/2008 11:31 AM

Yes - it has been done.

Others have addressed the concern about moisture, but another concern is ozone. DC motor brushes arc and give up ozone which is corrosive in high concentrations.

The Disney Tower of Terror (Florida, Anaheim, Paris) use AC units which are supplied chilled water. The 2,125hp DC motors have monitoring of air flow, humidity, and temperature. Air path is from outside, through the air handler with heat exchanger, through the motor, then back outside again.

With an AC motor (which does not generate ozone), the dried cooling air could be recirculated.

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Anonymous Poster
#10

Re: Electrical engineering

06/23/2008 5:20 AM

Watch this video from LeCroy!!
A technical Milestone is coming up!

http://www.youtube.com/watch?v=sP1_uc3bfLc

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