The torquespeed characteristics of a 60Hz induction motor an

The torque-speed characteristics of a 60-Hz induction motor and a load are shown in figure.

How many poles does the motor have?

In steady-state operation, find the slip. Neglect rotational losses.

Solution

from the characteristics it is evident that the speed is Ns=1800rpm

frequency f=60HZ

Ns=120f/P

P=120f/Ns

   =120*60/1800

    4

there fore motor has 4 poles

in steady state operation the intersection point of load and T-N characteristics will gives steady-state speed

that is Nr=1400rpm

slip(S)=(Ns-Nr)/Ns

          =(1800-1400)/1800

          =0.22