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Three phase Induction Motor torque/slip HELP NEEDED 
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#1
Jul514, 03:43 AM

P: 2

Hi, I'm really stuck on this assignment question and could do with a hand on the step by step process of how to get the answers.
A three phase induction motor as 2 poles, a standstill voltage of 121 v/phase (Er), rotor resistance of 0.15Ω/phase (Rr) and a standstill rotor reactance of 1.2Ω/phase (Xr) 1. Plot the torque against slip characteristic when the supply frequency is 50Hz for slip values of 1.0, 0.75, 0.5, 0.25, & 0.05 2. Determine the current in each phase of the rotor A) At start B) At maximum torque C) At full load torque if this occurs at a slip of 4% 


#2
Jul514, 09:18 AM

P: 54

Neglecting skin and proximity effect in rotor windingor squirrel cage
Irot=s*Er/sqrt(Rr^2+s^2*Xr^2) [A] Er[V] ,Rr,Xr [ohm] Tqmot=3*Irot^2*Rr/s/(2*pi()*f/p) [Nm] p=no.of pole pairs=1 For s=1 [at start] Ir=100 A Tq= 14.33 Nm For s=0.04 [rated] Ir=30.73 A Tq= 1691 Nm 


#3
Jul1214, 03:06 PM

P: 54

Sorry, I forgot the maximum torque slip calculation.
The maximum torque slip it is the slip calculated from dTq/ds=0. If Tq=3*I^2*R/s/(2*PI()*f/p) and I=s*Er/sqrt(R^2+s^2*X^2) then Tq =3*s^2*Er^2/(R^2+s^2*X^2)/s*R/(2*pi()*f/p) dTq/ds=3*Er^2/(2*pi()*f/p)*[(R^2+s^2*X^2)2*s^2*X^2]=0 X^2*s^2=R^2 s=R/X sm=0.15/1.2=0.125 


#4
Jul1314, 11:35 AM

P: 54

Three phase Induction Motor torque/slip HELP NEEDED
correction:
s=0.04 Tq= 33.81 ! s=0.125 Tq= 58.25 Sorry! 


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