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EMEC_II, TEE-501B.Tech. , Electrical Engineering, V semAssignment-2Q.1. A 75kW,440V,3phase,6pole,50Hz, wound rotor induction motor has a full load slip of 0.04 and the slip at maximum torque of 0.2 when operating at rated voltage And frequency with rotor winding short circuited at the slip rings. Assume the stator resistance and rotational losses to be negligible. Find:(a) Maximum torque (b) Starting torque (c) Full load rotor cu-lossThe rotor resistance is now doubled by adding an external series resistance. Determine:(a) Slip at full load (b) full load torque and (c) Slip at maximum torque.Q.2. A 3 phase, wound rotor induction motor has a star connected rotor winding with a rotor resistance of 0.12?/phase. With the slip rings shorted, the motor develops a rated torque at a slip of 0.04 and a line current of 100A. What external resistance must be inserted in each rotor phase to limit a starting current to 100A? what pu torque will be developed with rotor resistance starting?Q.3. Calculate the ratio of the transformation of an autotransformer starter for a 25kW, 400V, 3-phase induction motor if the starting torque is to be 75%of full load torque. Assume the slip at full load to be 3.5% and short circuit current to be 6 times full load current. Ignore magnetizing current of the transformer and of the motor.Q.4. The two cages of a 3 phase, 50Hz, 4 pole, delta connected induction motor have respective standstill leakage impedances of (2+j8) and (9+j2) ?/phase. Estimate gross torque developed(a) at standstill, the effective rotor voltage being 230V/phase, and(b) at 1450 rpm when the effective rotor voltage 8is 400V/phase. What is the gross starting torque if a star delta starter is used? Rotor quantities given are referred to the stator; the stator impedance is negligible.Q.5. the cages of a double-cage induction motor have standstill impedance of (3.5+j 1.5) ? and (0.6 + j7.0) ? respectively. The full load slip is 6%. Find the starting torque at normal voltage in terms of full load torque. Neglect stator impedance and magnetizing current.Q.6. A 50 Hz, induction motor wound for pole amplitude modulation has 20 ninitial poles and the modulating function has 8 poles. At what two speeds will the motor run?Q.7. Explain cogging and crawling phenomenon for 3-phase induction motor.Q8. Find the ratio of starting to full load current in a 10kW, 400V, 3-phase induction motor with star/delta starter, given that full load power factor is 0.85, the full load efficiency is 0.88 and the blocked rotor current at 200V is 40A. ignore magnetizing current.Q.9. Calculate the steps in a 5-section rotor starter for a 3-phase induction motor. The maximum starting current is equal to full load current. Full load slip = 1.8% with rings shorted. Rotor resistance per phase=0.015 ?.Q.10. What synchronous speeds can be obtained from the combination of 50Hz induction motor having 8 poles and 4poles. ................
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