Induction Motoro Rotor Copper losses

[scutzi128]

The question is:

The rotor of a 3 phase 60hz 8-pole induction motor takes 220w @ 3hz. Find the rotor speed and the rotor copper losses.

Here is what I have done so far:
I have found the rotor speed by using the equation slipspeed = fr(120)/P = 3hz(120)/8 = 45 rpm then finding nsync by 120(60)/8 = 900rpm so rotor speed = 900-45 = 855rpm. Slip can also be found to be 5% from this. I am stuck at trying to find the rotor copper losses though. I thought that it was just the 220w but that seems too easy. I would appreciate any help with this problem. Thank you.

 

[scutzi128]

Never mind I figured it out. It is slip*(input power to rotor) so .05*220w = 11w

 

[electricpete]

Pretty darned close.

If you want to get sharpen you pencil to get a hair closer:
1 - subtract out your estimate of stator losses and other non-rotor losses from input power first (that should leave you with airgap power).
2 - multiply by s/(1-s) instead of s

=====================================
(2B)+(2B)' ?

 

[jraef]

Naughty naughty, no homework help here... read the rules.


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