Increase Motor Capacity 4

[amy86]

Hello everyone! I'm looking into increasing a pulverizer motor capacity from 150HP to 250HP. Does anyone know of any good material on that? What methods are used to increase capacity, and what are the considerations? Thanks!

 

[ozmosis]

If you are increasing the power rating at the same operational speed then you will need to be aware of the complete transfer of power from the electrical supply through to the mechanical transmission. A few basic questions:
1) You seem to have determined that your power requirement needs to increase by 100hp. I would have to assume that you have done calculations to determine this fact.
2)To start, run and operate a motor with an increased power rating will obviously increase the current demand and therefore all the switchgear connected to the motor. It needs to have the increased capacity to do so. If you are starting the motor DOL then this is going to be included in the switchgear sizing. If the motor is using an electronic softstart or VFD, then again, this is required to match the motor.

3) The cabling may need to be increased.
4) The motor will be bigger so mechanically, you will need more space, different mountings for the motor and, however the motor is coupled to the pulverizer, will need to be modified.
5) More power at the same speed means more torque. The motor shaft will be bigger to accommodate the increased torque and therefore the coupling (if used) will be bigger. If there is a gearbox between motor and pulverizer, then this needs to be determined if it will cope with the increased torque.
6) looking at the actual pulverizer. Is this capable of the increased power/torque? There is no point in doing all this if the nett result is your actual pulverizing machine is what gets pulverized itself.

Just a few tips.
4)

 

[amy86]

Ozmosis, thanks for your comments. We did conduct a study and determined HP increase necessity. Do you know what options are there for HP increase? Would we need to add more coils or just increase temperature rating?

 

[Skogsgurra]

???
Add more coils?
You mean, install a new motor - and switching gear?

Gunnar Englund

http://www.gke.org

--------------------------------------
100 % recycled posting: Electrons, ideas, finger-tips have been used over and over again...

 

[edison123]

Buy a new motor matching your load, speed and torque.

Muthu

http://www.edison.co.in

 

[amy86]

Thanks all...buying a new motor would be the easy option. The price difference is the player here. That's why a motor rewind is being considered. Rewind should be done to increase magnatic flux density I believe, but not sure how is that achieved.

 

[rbulsara]

How do you now the 'magic' rewind will cost less than the new motor when you do not even know how it is achieved?

Rafiq Bulsara

http://www.srengineersct.com

 

[edison123]

"Increase the coils, Increase magnetic flux density" ???

Who is giving you these ideas ?

You can't get 66% more power from the same motor unless there is a corresponding increase in motor speed. And there are mechanical and electrical design issues with increasing the motor speed. You can't do it just like that.

Buy a new motor.





Muthu

http://www.edison.co.in

 

[LionelHutz]

You are seriously expecting to increase the motor capacity by 67%?

Install a very chilled forced air cooling system...

Increase the voltage and frequency by 67% and then installing a reduction drive to bring the speed back down...

Honestly, good luck.

 

[electricpete]

If you can find an off the shelf interchangeable motor, it is an absolute no brainer that will be cheaper and probably more reliable. You may run into problems with the frame size though...(what is the speed voltage and frame size?)

Uprating a motor is sometimes done but generally reserved for larger motors and smaller incremental changes. Often for medium voltage form wound motors there is an improvement by improved insulation materials operating at higher volts per mil which allows adding more copper. I'm guessing your motor is a low voltage random wound and there is not much savings in insulation size to be realized. There are a few other tricks that rewinders like edison and others here use: higher slot fill, higher flux density, higher temperature rating on insulating materials...but probably will need a whole lot of tricks and some magic to get that much increase.

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[amy86]

Thanks again everyone. electricpete...the motor is: 480v, 600 RPM, GE, frame size: 6345s. It's an old motor, and not sure if it is random wound. I guess u guys are right, I should consider buying a new motor first. You mentioned adding more copper. Could you please explain how that increases flux density? Can they use different iron laminations with bigger slots if frame size is an issue? I imagine existing iron is an other consideration if more flux density is expected.

 

[waross]

This was done many years ago when the old NEMA frame motors were uprated to the U frame motors. By using thinner and more heat resistant insulation they were able to upgrade from NEMA frames to U frames with a significant HP increase. The 40 or 50 years ago motors were again upgraded to the T frame motors used today. Many T frame applications develop twice the HP of the same frame size under the old NEMA sizing. When the insulation is thinner, larger copper diameter conductors may be used in the same slots. Add the ability of the modern insulating material to run at higher temperatures and you can get more HP out of a given frame size. The compromise is a lower PU peak torque and a lower allowable locked rotor time before burnout.
But, the limit has about been reached. Now, the solution to more power is to use over voltage and over frequency and gear or belt back down to the speed that you need.
This works fairly well with 230/460V motors rated for inverter duty. All the windings are suitable for the application of 460 Volts so the motors are connected for 230 Volts and supplied with 460 Volts at 120 Hz. This technique is used by some skid mounted equipment manufacturers for new equipment but it isn't a good idea for older non inverter duty motors. The PWM wave form tends to destroy older motors.
Flux density is not an immediate problem. The primary issue is dissipating the I²R losses.That is why we want a greater cross section of copper or the ability to run hotter. Breakdown torque may not increase so starting heavy loads may present issues.

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

 

[jraef]

Increase the voltage and frequency by 67% and then installing a reduction drive to bring the speed back down...

(and similar comments by Bill)

Don't forget that when you do this, you have added mechanical losses to the equation, probably at least 20% (80% eff through the gearbox) so that 67% increase probably goes to a 100% increase before the gear-down (1.67 /.8).

So to take that out to a conclusion with the goods at-hand, to get 250HP net at the shaft from an existing 150HP 460V 60Hz motor, you will need to add a VFD running at 120Hz and increase the input voltage to 920V. Your throughput efficiency will drop precipitously.


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[waross]

Hi jraef;
How about reconnecting for 230 and using 480 Volts? Not that the old motor will last long on PWM service.

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

 

[LionelHutz]

Well, I did a quick search and found references to a GE frame 6345S motor sized 300hp, 600rpm, so in your case this does sound feasible.

Go here and search for 6345S in the top search box.

http://www.surplusrecord.com/adv_search.html

There are a few induction and wound rotor motors listed there with the appropriate size.

Is this a wound rotor motor? If so, then the rotor and stator may both need re-worked to upgrade the HP. To me, that sounds like a motor that was built to match a specific specification, in other words a custom ordered motor.

You really need an expert to evaluate your motor and tell you what could be done. We can't teach you how to be an expert at this over the internet.

 

[Tmoose]

Got a 100 HP 600 rpm motor lying around? Or a second 150 HP motor? Depending what the back of the existing motor looks like, a few couplings and some I-beams and channel might allow you to do something like this.

http://www.dynesystems.com/images/email-images/tandem2025s-300-Web.jpg

 

[electricpete]

Tandem - weird stuff.

It sounds like Lionel found some very promising leads. For example:

http://www.surplusrecord.com/cgi-bin/adpop.pl/?289595

MOTORS, A.C., SQUIRREL CAGE, 60 CYCLE (Also See Explosion Proof) 300 HP 590 RPM General Electric, Fr.6345S, DP SB, 460 V. (5)

Same frame number means proper mechanical interchangeability. Same horsepower, speed, voltage.

There might be a few smaller details to check:
* Term box on correct side (if not can you move it.... or can you adapt your wiring).
* Is the enclosure suitable for your environment.
* Proper accessories (space heaters with correct voltage). Or can you backfit, or adapt to what they've got.
* Since it's a surplus....Is the motor in working order? Does it run? With acceptable vibraiton? Has it been meggered / bridged? Or is there a warranty?
* Is it the right color? (Just kidding).

Also as mentioned you'll have to check your cables and breakers for capacitity as well as setpoints to permit starting and running. That will be the case for any 250hp 460vac solution you pick.

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[amy86]

Guys, I appreciate your help. I'm gonna follow Lionel's lead. Also, I'm going to have a winding expert take a look at it, and based on the recommendation everyone posted here, I'm in a very good position to discuss with them different alternatives. I'm gonna post what solution the expert recommends and maybe I can take advantage of your thoughts again. Thanks a lot!

 

[LionelHutz]

I was pointing out those motors more as examples of what HP was available in that frame size and not just to buy one. However, both are options and just buying one might be simpler.

 

[ozmosis]

You might be able to get more 'power' out of a motor but consider at all the factors in the transmission of this power and the subsequent torque developed throughout the system. For example, motor shafts are a certain diameter to cope with the torque developed. Most have a large margin to overload but shafts do break.