(13) For a certain polyphase induction motor, which at full load operates at its maximum power factor, the starting current and the no-load current at full voltage Assuming the rotor and stator copper...

Please solve Question(13)

Extracted text: (13) For a certain polyphase induction motor, which at full load operates at its maximum power factor, the starting current and the no-load current at full voltage Assuming the rotor and stator copper losses are equal, determine the percentage reduction in voltage which would just permit stable operation at a torque not exceeding the full-load value. What would be the power factor and slip at full-load (14) A 400-hp, 1100-V, 3-phase induction motor gave the following data during [APPENDIX E] ELECTRICAL MACHINES AND THEIR APPLICATIONS are short-circuited. 720 rev/min in the opposite direction to the rotating field; i.e. plugging, Show th the total input to the machine is equal to the sum of all the losses. Note that the that copper loss will appear in the control lead, the control terminals bein shootor CU (a) (b. cuited in this case. (10) A 6-pole induction generator operates at 50 Hz, 88:5 kVA, 0-77 p.f. leading and at a line voltage of 500 V. The stator is star-connected and the rotor runs a 1,030 rev/min to generate this power. Calculate the constants of the approximate equivalent circuit given that the machine takes 55.5 A at 0-1 p.f. when running at synchronous speed from 500 V. The stator and referred rotor resistances may be assumed identical. Note. Problems (11) to (15) are intended to be solved by using a circle diagram. (11) On no load at 500-V, a certain 3-phase, 50-Hz, 4-pole induction motor takes 16 A at a power factor of 0-2. With the rotor locked and 125 V applied, it takes 37-5 A at 0-3 p.f. If, when the motor is running at full load and supplied at 500 V, the power factor is at its maximum, estimate the full-load current, power factor, torque, speed, output and efficiency. Also estimate the starting torque and maximum torque at full line voltage. Assume R2' = 1-3 R1. By considering the circle diagram and its basis, how would you expect the per- formance to be affected if the motor was run from a 500-V, 60-Hz supply? (12) A 3-phase, 4-pole, 440-V, 50-Hz slip-ring induction motor is started at full voltage uncoupled from its load. When a fixed external rotor resistance of value four times the rotor resistance itself is inserted at starting, the starting current and power factor are respectively 200 A and 0-6. The motor runs up to speed and the slip rings are then short circuited. On steady conditions being achieved the current and power factor become 12-5 A and 0-2. Assuming R1 = R2', (a) Estimate the maximum torque and the total external resistance, expressed n terms of the rotor resistance, required to get this torque at standstill with 1un voltage applied. (b) What would be the line current if started from full voltage without externial rotor resistance? (c) How much external rotor resistance wonld be required to double the naturar starting torque ? (c) for otl qu hp ati du te 8 to th 2- are in the ratio of 10/1 and the power factor in each case is 0-25. torque with the voltage thus reduced? 642