A 600V line powers a three-phase induction motor with a nominal power of 100 hp (≈ 75 kW). Two wattmeters placed in the line wires indicate a total power of Pa = 70kW and an amperemeter indicates a line current of Ia = 78A. Accurate measurements indicate a speed of rotation of N = 1463 rpm. In addition, the following information is provided:
– The iron losses in the stator: Pfs = 2kW
– Ventilation and mechanical losses: Pmec = 1.2kw
– Resistance between two stator terminals : 2×Rs = 0.34Ω
We suppose STAR connexion.
1- Give the number of poles of machine stator and the slip s of the machine
2- Calculate the stator joule losses Pjs
3- Calculate the electromechanical power delivered to the rotor Pem
4- Deduce the joule losses in the rotor Pjr
5- Calculate the useful torque Tu of the motor
6- Calculate the efficiency of the motor η