Problem set Equipment 2

1. A 460 V, long shunt compound motor has armature and series field resistances of 0.2 ohm and 0.1 ohm, respectively. It runs at 550 rpm when unloaded and taking an armature current of 5 A. calculate the speed in rpm at which it will run when taking an armature current of 100A. assuming series field increases the flux by 10%. 468.9rpm

2. A 250 V. dc series motor has an armature and series field resistances of 0.2 ohm and 0.1 ohm respectively. It takes a current of 35 A when running at 700 rpm, calculate the current taken from the source if the field is shunted by a resistance of 0.1 ohm and the load torque is increased by 30%. 56.43A

3. A 10 HP, 460 V shunt wound runs at 1000 rpm on full torque. The full load efficiency is 87% and the armature and shunt field resistances are 1.1 ohm and 500 ohms respectively. Calculate the additional resistance required in the armature circuit to give a speed of 700 rpm when the current taken from the supply is half of the full load current. 16.95 ohms

4. A motor runs on a 5 minute duty cycle having 20 kW load for half the time and no-load for the rest of the time. Theoretical continuous rating of the motor suitable for the duty is __ kW. 14.14kW

5. A brake mounted on a 200 hp, 450 rpm motor has a torque rating of 3,141 N-m. the rotating part has a moment of inertia of 33 kg-m^2. The stopping time for the motor in seconds is. 0.495 sec

6. A pump is driven at 72 rpm by a 3 phase, 60 Hz 8 pole induction motor. If the slip is 4% find the gear ratio between the motor and the pump. 12

7. When the line voltage of an induction motor is reduced to 80% of its rated value, then the starting current will be reduced by ___% 20

8. A squirrel cage induction motor develops a maximum torque of 2.25 times of its full load torque and has rotor standstill leakage reactance which is 4 times the rotor resistance per phase. Determine the full load percent slip. 5.8%

9. The maximum torque of an induction motor is 100 kg-m at a slip of 12%. Determine the torque in kg – m at a slip of 6%. 80 kg- m

10. A 10 Hp, 440 V 14.1 A 60Hz 3-phase induction motor has full load speed of 1750 rpm. If the motor is operated from 370V, 50 Hz, 3-phase source and delivering its rated torque, determine the speed. 1441 rpm