A three phase squirrel cage induction motor has the nameplate data shown in Table I below

 Table I : Induction Motor Nameplate Data.

a)  Calculate the induction motor efficiency for the load test.

b)  It is required to supply the same torque at a speed of 1200rpm. Approximately, determine the supply voltage and frequency required to achieve this speed and torque condition.

[Hint: Neglect the effects on the induction motor variable speed torque response due to R1 and the mechanical losses.]

c)  Explain why the supply frequency must change from 50Hz in order to achieve the loading condition.