- Three phase induction motor has rating of 50 kW, 960 rpm, 400 V. 50 Hz, 6-pole. The motor parameters are R = 0.08 , R = 0.1 , X = X = 0.3 2 and the moment of inertia 10 kg- m². It is required to stop the motor from its no load speed under reverse breaking operation. Find the required value of external resistance that need to put in rotor circuit such way that breaking will be achieved with minimum time. What is breaking time.

7. The total rotational losses of an induction motor are a combination of ------- A) Friction losses B) Windage losses. D) Stray losses. C) Core losses. 8. The developed mechanical power can be calculated using the equation of- A) PAG - PRCL. B) PAG w sync C) (1-s) PAG. D) 3 E2Gc. 9. For an induction motor, if the synchronous speed is 1800 r/m, and the rotor speed 180rad/sec, then the slip will be: A) 5.5% C) 6% B) 4.5% D) 4% 10. The power losses in the stator part of the induction motor are B) Core losses D) Friction and windage losses A) Stator copper losses C) Air-gap losses

3. A 440V 60-hp six pole 60 hz A connected induction motor has the following parameters R1=0.048 R2= 0.035 Xm= 9.50 X1= 0.33 0 X2= 0.37 0 Pcore= 600W PF&W= 350W Use the Thevenin's Equivalent circuit concept to find: (a)Vth and Zth seen by the rotor circuit (b)The slip at which maximum torque occurs (c) the value of Max/pullout Torques (d) The starting torque.

A 3 phase, 1500 rpm, 2200 V, star connected synchronous motor has an impedance of 0.4+j90 per phase. At some excitation 2900 V is induced in the armature. Find the maximum torque developed by motor before the motor breaks out of synchronism. Also find the load angle this time.