Q4.a) List the factors that determine the starting torque of the three-phase induction motor. How does this torque generally compare with the value of the rated torque (6)
b) An 18.65 KW, 6 Pole, 50 Hz, 3 phase slip ring induction motor runs at 960 rpm on full load with a rotor current per phase of 35 A allowing 1 KW for mechanical losses, find the resistance /phase of three-phase winding. (10)
Q5.a) With the aid of delta and star connection diagrams, state the basic equation from which the delta -star and star- delta conversion equation can be derived (6)
b) A 230/115 V, single phase transformer is supplied with a load of 5A at p.f. 0.86 lagging. The no-load current is 0.2 A at p.f. 0.208 lagging. Calculate the primary current and p.f. (10)
Q6. A 3000 KVA, 6-pole 3 phase, star connected alternator runs at 1000 r.p.m. in parallel with other machines on 3300V bus-bars. The synchronous reactance is 25%. Calculate the synchronizing power for one mechanical degree of displacement and the corresponding synchronizing torque. (16)
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