edriveqbanksem7 (1)

7/30/2019 edriveqbanksem7 (1)

1/10

Guru Tegh Bahadur Institute of Technology

Department of Electrical and Electronics Engineering

Semester - 7

Electric Drives - ETEE 401

Question Bank

1. For low speed high power reversible drives

a) Cycloconverter fed ac drives are suitable.

b) Current source inverter fed ac drives are suitable

c) Voltage source inverter fed ac drives are suitable

d) Induction motor fed from ac voltage controller are suitable

2. The operation of ac motors fed from Current source inverters characterized by

a) Sinusoidal line voltage

b) Peaky armature voltage

c) Good harmonic torques

d) Sinusoidal armature voltage with spikes

3. A here phase ac voltage controller feeding a three phase induction motor has an output

of

a) Constant voltage of variable frequency

b) Variable voltage of variable frequency

c) voltage of Constant frequency

d) Constant voltage of Constant frequency

4. A three phase ac voltage controller feeds an induction motor. The motor has

Faculty: 1. Harshpreet Kaur

2. Kavita Jha


2/10

a) Very good efficiency and power factor at all speeds.

b) Very good efficiency but poor power factor at all speeds.

c) poor efficiency but good power factor at all speeds

d) poor efficiency and poor power factor at all speeds

5. The method of speed control using a three phase voltage controller is suitable for loads

a) whose torque is proportional to speed

b) having constant torque

c) whose torque is proportional to square root of speed

d) having torque proportional to square of speed

6. A three phase induction motor having speed control using chopper controlled

resistance is characterized by

a) poor power factor and good efficiency

b) poor efficiency and poor power factor

c) good efficiency and poor power factor

d) good power factor and poor efficiency

7. A three phase induction motor with chopper controlled resistance has its torqueproportional to

a) rotor current

b) square of rotor current

c) stator resistance

d) square root of rotor current

8. A three phase induction motor having a combination of diode rectifier and line

commutated inverter in the rotor circuit can give

a) speeds below synchronous speed only

b) speeds above synchronous speed only


2. Kavita Jha


3/10

c) both sub and super synchronous speeds

d) speeds varying 0 to 50% of synchronous speeds

9. The motor having slip energy recovery scheme can be braked by means of

a) regenerative breaking

b) plugging

c) dc dynamic breaking

d) all the methods of a,b,c

10. The three phase induction motor having sub synchronous converter cascade in the

rotor circuit is characterized by

a) good power factor and poor efficiency

b) good power factor and good efficiency

c) poor power factor and poor efficiency

d) poor power factor and good efficiency

11. Equal area criterion gives information regarding the

a) transient stability of a synchronous motor

b) steady state stability of a synchronous motor

c) steady state stability of an induction motor

d) transient stability of an induction motor

12. Retardation test is employed

a) to determine the losses of the motor

b) to determine the moment of inertia of the rotating parts

c) to determine the speed torque curve of the motor


2. Kavita Jha


4/10

d) to determine the overload capacity of the motor

13. In the drive system all the mechanical quantities are referred to a single rotation shaft

using the principal of

a) power invariance

b) torque invariance

c) conservation of momentum

d) All a,b,c

14. Active load s

a) have the capacity to accelerate as well as decelerate the drive motor

b) have the capacity only to oppose the motion trying to retard the motor

c) have the capacity to provide accelerating torque only

d) all the above

15. A typical active load is

a) Hoist

b) Blower

c) Pump

d) Lathe

16. A fully controlled line commutated converter operates as an inverter

a) In the range of firing angles 0


5/10

c) In the range of firing angles 90


6/10

a) Enables the inverter operation

b) Smoothens the load current consequently the smoothing inductance required is

small

c) Makes the converter draw additional reactive power

d) Impairs the line power factor

21. A phase controlled converter is designed for 220v, 50Hz supply .If this converter

operates on 170v, and 50 Hz supply there is a possibility for

a) Commutation failure during rectification

b) Commutation failure during inversion

c) Increased voltage drop

d) Increased losses in the inverter

22. Mid point converters in general require input transformers .The input transformer is of

special construction because

a) Harmonic currents are present in the load

b) Dc magnetization

c) To give strength to the system

d) To improve the converter behavior

23. A voltage source inverter supplying an inductive load requires a gate pulse of long duration

to turn the thyristor ON

a) To ensure the initiation of conduction of the thyristor immediately when its voltage is

positive

b) because a wider pulse is required invariably to urn on the thyristor

c) To reduce the thyristor losses

d) Because a wider pulse effectively provide an output with least harmonics


2. Kavita Jha


7/10

Content

24. The phase control employed for a cycloconverter imparts

a) A very good power factor

b) A very bad power factor

c) Undesirable harmonic behavior

d) Poor voltage regulation

25. The conduction angle of an ac voltage controller depends on

a) The variation in the input voltage

b) The impedance angle of the load

c) The supply frequency

d) Both supply frequency and voltage

26. In a two quadrant chopper the load voltage is varied from positive maximum to negative

maximum by varying

a) Time ratio of the chopper from 0 to 1.

b) Time ratio of the chopper from 1 to 0.

c) Time ratio of the chopper from 0 to 0.5.

d) Time ratio of the chopper from 0.5 to 0

27. A dual converter with circulating current mode

a) has no possibility of discontinuous conduction

b) Requires a most sophisticated control

c) has a very sluggish behavior

d) Offers difficulties during transition from motor to generators.

28. The disadvantage of load commutation is

a) Harmonic torques


2. Kavita Jha


8/10

b) Loss of efficiency due to losses

c) The speed from 0 to 10% of base speed is not possible

d) The peed control range is limited to 0-10% of base speed.

29.By self control of a synchronous motor we mean that

a) elimination of torque ripple

b) the speed of the motor is varied in steps

c) the speed of motor is function of input frequency.

d.) the input frequency is controlled from the speed of motor.

30. While operating a phase controlled converter the commutation capability of the motor

deteriorates because of

a) increase in the RMS current

b) harmonic content of armature current

c) peak value of armature current

d) peak value of armature current, harmonic content of armature current and possible

discontinuous conduction.

31. A 3- AC voltage controller feeding a 3- IM has an output of

a. Constt. Voltage of variable frequency, fb. Variable V of variable f

c. Variable V of constant f

d. Constant V of constant f

32. A 3- AC voltage controller feeds an IM. The motor hasa. Very good efficiency and power factor pf at all speeds

b. Very good but poor pf at all speedsc. Poor but good pf at all speedsd. Poor and poor pf at low speeds

33. A 3- IM having speed control using chopper controlled resistance is characterized by


2. Kavita Jha


9/10

a. Poor pf and good

b. Poor and poor pf

c. Good and good pfd. Good pf and poor

34. A 3- IM with chopper controlled resistance has its torque proportional to

a. Rotor currentb. (rotor current)2

c. Stator resistance

d. (Rotor current)0.5

35. A 3- IM having a combination of diode rectifier and line commutated inverter in the rotor

circuit can give

a. Speeds< synchronous speed only

b. Speeds > synchronous speed onlyc. Both a. and b.

d. Speeds varying from 0 to 50% of synch speed

36. A motor having slip energy recovery scheme can be braked bya. Regenerative braking

b. Plugging

c. DC dynamic brakingd. All of above

37. The speed of an IM can be varied by variable frequency supply from a static powerconverter. A simultaneous voltage variation is also effected in order to

a. To avoid saturation and provide optimum torque capabilityb. To decrease the torque pulsations

c. To limit peak stator current

d. To minimize additional losses

38. A CSI fed IM is inherently unstable when it operates on

a. Open loop

b. Closed loop

c. A variable frequency supply keeping air gap flux constantd. A var. frequency supply keeping stator flux constant

39. A 3- IM operates at constant rotor frequency when the stator frequency is varied from zeroto rated value. The torque developed by the motor is


2. Kavita Jha


10/10

a. Constant from 0 to rated speed

b. Proportional to speed

c. Proportional to (speed)2

d. Inversely proportional to speed

40. For low speed high power reversible drives, which is suitable

a. CSI fed AC drivesb. Cycloconverter fed AC drives

c. VSI fed AC drives

d. IM fed from AC voltage controller

41. Operation of AC motors fed from CSI is characterized by

a. Sinusoidal line voltage

b. Peaky armature voltagec. Good harmonic torques

d. Sinusoidal torques


2. Kavita Jha

edriveqbanksem7 (1)

Documents