Induction vs Synchoronous Motors

[Hertz]

I am looking for a graph of hP/rpm, showing the suitability of induction/synchoronous motors. Any Ideas?

 

[dpc]

Not without a little more information than that. Suitability for what? Induction motors are available for virtually any speed and size. Synchronous motors offer some advantages in large size/slow speed applications in terms of efficiency and power factor, but will generally cost more.

 

[electricpete]

At one time there was a rule that sync motor should be considered if horsepower is higher than rpm.

I don't like the complexity of sync motors... more to maintain and fail.

They may have advantages in terms of efficicency and power factor.

Try searching for old threads on this recurring subject. There is a good paper from GE on comparison of sync and induction motors that I linked to several of those old threads.

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[jraef]

I'm with dpc. Are we speaking of 1250HP ball mill motors, or are we speaking of 50W clock motors? "Synchronous" describes them all.

Eng-Tips: Help for your job, not for your homework Read faq731-376

 

[Hertz]

Thanks all for your good comments. I am going to be more specific. We are trying to buy two reciprocating compressors, one rated at 10,000 hP, and the other at 1,500 hP., both 360 RPM, 6.6 kV, 60 Hz. How do we decide on induction/synchoronous. I remember seeing a graph as I described in my original posting, but I can not find it in my files.

electricpete: Do you remember what the GE link is?

 

[RalphChristie]

I suppose the link electricpete mentioned is:

http://www.geindustrial.com/products/reference/GEZ-6209.pdf

 

[electricpete]

Yes that's the one. Thanks Ralph.

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[motorspert]

hertz
The GE paper is written with a bias towards synchronous machines and in the modern world induction machines are more suitable at some high ratings. Having said that, for your application, (ie low speed) induction motors will have pretty poor powerfactors. From that viewpoint synchronous is certainly the best candidiate at 10,000HP. For the smaller rating either would do the job, but the synchronous motor may well edge it.

 

[EEJaime]

ElectricPete, the link Ralph sent also has the "rule of thumb" you mentioned but it is stated as "...if the horsepower is TWO times the rpm...". Just a clarification.