AC motor speed help!

AC motor speed help!

PostBy: anthony7812 On: Sat Jul 28, 2012 2:52 pm

I understand 'slip' as the speed difference between the rotor and magnetic field. My question is... is slip a factor in motor speed that should be considered or does that just deal with torque. any help would be awesome. I need a relatively straight forward response. I understand their are a ton of variables related.
anthony7812
 
Stoker Coal Boiler: VanWert VA 400
Coal Size/Type: Buck/Anthracite

Re: AC motor speed help!

PostBy: Short Bus On: Sun Jul 29, 2012 3:37 am

I'll take a swing at this one.
Motor "slip" increases with load, the more load the slower it turns.
If you increase the gap between the field and the armeture you increase the slip, this is bad for power factor, and effieicency, but good for soft start, and overloading.
Three phase motors slip less.
Short Bus
 
Stoker Coal Boiler: Kewanee boiler with Anchor stoker
Coal Size/Type: Chestnut / Sub-bituminous C
Other Heating: Propane wall furnace back up only

Re: AC motor speed help!

PostBy: anthony7812 On: Sun Jul 29, 2012 4:01 am

i understand that varying frequency and number of poles will determine motor speed(and a few other factors). The nameplate RPM, say 1800rpm for shits and giggles, would slip be looked at in that rpm determination.
anthony7812
 
Stoker Coal Boiler: VanWert VA 400
Coal Size/Type: Buck/Anthracite


Re: AC motor speed help!

PostBy: Short Bus On: Sun Jul 29, 2012 12:12 pm

Correct frequency determins speed, slow your generator down and all the motors slow down.
Probalby 50 to 100 RPM of slip is practical.
Look at some motor tags, bench grinder, table saw, and so on, the RPM will vary form 1775, 1750, 1725 and all these motors are threoredically going to spin 1800 RPM, no load.
Motor with lower speeds have more slip, and better starting torque, within thier speed group, unrelated to poles.
Motors and generators have certain RPMs 3600, two pole, 1800 four pole, 1200 six pole, 900 eight pole
I have seen 900 RPM 50 KW generators massive, compared to 1800 RPM sets.
Nominal 1800 RPM motors have four poles, nominal 3600 RPM motors have two poles, and half the starting torque, half the copper also.
All betts are off on hand tool motors, brushes and other things change the speed.
Also as far as slowing the generator down for different speeds the new computerised generators are a bit funky in this area.
Short Bus
 
Stoker Coal Boiler: Kewanee boiler with Anchor stoker
Coal Size/Type: Chestnut / Sub-bituminous C
Other Heating: Propane wall furnace back up only