9 Questions

Questions and Answers

- 1.A shunt DC motor operates at 700 rpm when an armature of 18 A from a 230-V supply. If the armature resistance is 0.25W, calculate the no-load speed, assuming that all output losses are negligible.
- A.
700.0 rpm

- B.
778.5 rpm

- C.
714.0 rpm

- D.
687.2 rpm

- 2.Find the output torque of a DC motor whose output power is 1200 W and whose shaft speed is 1200 rpm.
- A.
1.00 Nm

- B.
60.0 Nm

- C.
0.105 Nm

- D.
9.55 Nm

- 3.A 110V series DC motor has an armature resistance of 0.3W and a field resistance of 0.2W. The motor is running off a 110V DC power supply and draws a line current of 20A and rotates at 1500 rpm while driving a mechanical load. The rotational loss of the motor is 250W. Calculate the efficiency of the motor.
- A.
79.55%

- B.
70.45%

- C.
87.5%

- D.
61.36%

- 4.A 3-phase, 6-pole, induction motor is supplied with a 240V, 50 Hz supply and draws a current of 35A at a power factor of 0.75 and has a full-load slip of 2.0%. The total copper loss and iron loss in the stator is 350W. Calculate the input power, P
_{in, }of the induction motor.- A.
14198 W

- B.
10562 W

- C.
10912 W

- D.
14548 W

- 5.A 4-pole induction motor is energised by 3-phase, 50 Hz supply. The motor (rotor) runs on full-load at 5 percent slip. Determine:- (i) The speed of the rotating magnetic field (n
_{s}) (ii) The frequency of the stator currents (f_{s})- A.
1,500 rpm, 50 Hz

- B.
1,500 rpm, 2.5 Hz

- C.
1,425 rpm, 50 Hz

- D.
1,425 rpm, 2.5 Hz

- 6.A DC shunt motor is connected to 230 V DC power supply. The motor has an armature resistance of 0.8 ohm and a field resistance of 100 ohms. The motor draws a current of 12A and rotates at 300 rpm at full load. Find the input power.
- A.
2760 W

- B.
3000 W

- C.
2880 W

- D.
529 W

- 7.In the 3-phase induction motor, if the rotor moves at the same speed as the magnetic field
- A.
The slip will be 1

- B.
The torque will be maximum

- C.
The slip will be zero

- D.
The torque will remain unchanged

- 8.A 100V DC series motor runs at 1500 rpm with a line current of 20A. The armature resistance is 0.3W and the field resistance is 0.2W. Find the power developed.
- A.
1800 W

- B.
1880 W

- C.
1920 W

- D.
2000 W

- 9.An induction motor is running at a slip of 0.1. The input power is 2000W. The stator copper loss and core loss is 200W. The rotational loss is 50W. What is the rotor copper loss?
- A.
1750W

- B.
180W

- C.
175W

- D.
200W