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Synchronous motors below 2MW rating
4

Synchronous motors below 2MW rating

Synchronous motors below 2MW rating

(OP)
Client specification says Synchronous motors shall not be used below 2MW rating.
Use of Synchronous motors at higher ratings such as 10MW is because of improved efficiencies. This advantage may not be there at lower rating (such as 2MW etc.).
But, why "shall not" in the spec. Could there be some other technical reason other than efficiency (and ofcourse cost)!!
Thanks in advance.

RE: Synchronous motors below 2MW rating

Synchronous machines are more expensive than cage/wound rotor motors. May be below 2 MW, the efficiency increase does not justify the cost enough ?

RE: Synchronous motors below 2MW rating

2
More expensive in initial cost, more complex, more maintenance effort to maintain, more things to break (potentially lower reliability).

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RE: Synchronous motors below 2MW rating

pete

IIRR, you posted a GE link on synch vs induction motors some time back. Do you still have it with you ?

RE: Synchronous motors below 2MW rating

Thanks pete.

raghun - That GE piece should answer some of your questions.

RE: Synchronous motors below 2MW rating

(OP)
Thanks pete and edison.
The GE document is quite good. It has a lot that I didn't know before. One thing that I found particularly interesting is that - if the motor HP rating happens to be twice or more of the motor rated RPM, then the Synch motor is cheaper than the Cage induction one.

RE: Synchronous motors below 2MW rating

Yes, slow speed operation is one other advantage of synchronous motors. Slow speeds in cage motors means lower efficiency. In days gone by, you would see a lot more smaller synch. motors on direct-drive low speed constant loads such as air compressors. I did a retrofit on one foundry project where they had 7 500HP 2300V synchronous air compressors installed in the 1940s, mainly because they needed 560 RPM, but also to correct the PF in the entire plant since the air compressors ran 24/7/365. But over time the rest of the Steel Mill shut down and was sold off piecemeal, so the remaining foundry had no other appreciable induction loads needing pf correction, and the compressors no longer ran 24/7. So in turning them on and off repeatedly, the maintenance headaches of having that many synch. motors became evident really fast.

But air compressor designs changed to allow higher speed motors and for anything else, using VFDs on small low speed aplications is a much better way to accomplish that now.


"If I had eight hours to chop down a tree, I'd spend six sharpening my axe." -- Abraham Lincoln  
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RE: Synchronous motors below 2MW rating

Quote:

...using VFDs on small low speed applications is a much better way to accomplish that now.

It sure is when you're making or selling them! tongue

Wonder how many VFDs made today will still be running in sixty years time? ponder Wonder how many of us will be around to find out! lol
  

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If we learn from our mistakes I'm getting a great education!
 

RE: Synchronous motors below 2MW rating

Hey Scotty, I wonder how many factories that install ANYTHING anymore will be around long enough to see the warranty expire! banghead


"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: Eng-Tips.com Forum Policies  

RE: Synchronous motors below 2MW rating

How do you guys embed those smileys here ? I tried to do that with images from mysmiley.net but just get a red star.

RE: Synchronous motors below 2MW rating

 
edison123—

Scroll down to the reply window, and centered below that window it an "Emoticons/Smileys" link and check box.
   
—busbar
    

RE: Synchronous motors below 2MW rating

(OP)
Thanks jraef. It is a good insight in to the world of low kW Synch motors, which are a rarity these days.

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