Download 1 - gtbit

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)
b)
c)
d)
Cycloconverter fed ac drives are suitable.
Current source inverter fed ac drives are suitable
Voltage source inverter fed ac drives are suitable
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)
b)
c)
d)
Constant voltage of variable frequency
Variable voltage of variable frequency
voltage of Constant frequency
Constant voltage of Constant frequency
4. A three phase ac voltage controller feeds an induction motor. The motor has
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
Faculty: 1. Harshpreet Kaur
2. Kavita Jha
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)
b)
c)
d)
poor power factor and good efficiency
poor efficiency and poor power factor
good efficiency and poor power factor
good power factor and poor efficiency
7. A three phase induction motor with chopper controlled resistance has its torque
proportional to
a)
b)
c)
d)
rotor current
square of rotor current
stator resistance
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)
b)
c)
d)
9.
The motor having slip energy recovery scheme can be braked by means of
a)
b)
c)
d)
10.
speeds below synchronous speed only
speeds above synchronous speed only
both sub and super synchronous speeds
speeds varying 0 to 50% of synchronous speeds
regenerative breaking
plugging
dc dynamic breaking
all the methods of a,b,c
The three phase induction motor having sub synchronous converter cascade in the
rotor circuit is characterized by
a)
b)
c)
d)
good power factor and poor efficiency
good power factor and good efficiency
poor power factor and poor efficiency
poor power factor and good efficiency
Faculty: 1. Harshpreet Kaur
2. Kavita Jha
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
d) to determine the overload capacity of the motor
13.
In the drive system all the mechanical quantities are referred to a single rotation
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<= α<=90
b) In the range of firing angles 90<= α<=180
c) In the range of firing angles 90<= α<=180 with a suitable dc source in the
load
d) When it supplies RLE load
Faculty: 1. Harshpreet Kaur
2. Kavita Jha
shaft
17. The inverter limit of a line commutated inverter is due to
a) overlap alone
b) turn off time of the thyristor
c) turn on time of the thyristor
d) Due to both overlap of the converter and turnoff time e of the thyristor.
18. The overlap introduces
a) Additional reactive power requirement
b) Additional losses in the load
c) Additional harmonics in the load current
d) A heavy short circuit current
19. In the thyristor power converters during discontinuous conduction
a) The load current is zero even though the load voltage is present
b) Load current and load voltage are both simultaneously zero
c) The load current is present even though the load voltage is zero
d) The current is ripple free.
20. A free wheeling diode in a phase controlled rectifier
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
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
Faculty: 1. Harshpreet Kaur
2. Kavita Jha
transformer is of
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
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
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
Faculty: 1. Harshpreet Kaur
2. Kavita Jha
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-Ф AC voltage controller feeding a 3-Ф IM has an output of
a.
b.
c.
d.
Constt. Voltage of variable frequency, f
Variable V of variable f
Variable V of constant f
Constant V of constant f
32. A 3-Ф AC voltage controller feeds an IM. The motor has
a. Very good efficiency η and power factor pf at all speeds
b. Very good η but poor pf at all speeds
c. Poor η but good pf at all speeds
d. Poor η and poor pf at low speeds
33. A 3-Ф IM having speed control using chopper controlled resistance is characterized by
a. Poor pf and good η
b. Poor η and poor pf
c. Good η and good pf
d. Good pf and poor η
34. A 3-Ф IM with chopper controlled resistance has its torque proportional to
a. Rotor current
b. (rotor current)2
c. Stator resistance
d. (Rotor current)0.5
35. A 3-Ф 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 only
Faculty: 1. Harshpreet Kaur
2. Kavita Jha
c. 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 by
a. Regenerative braking
b. Plugging
c. DC dynamic braking
d. All of above
37. The speed of an IM can be varied by variable frequency supply from a static power
converter. A simultaneous voltage variation is also effected in order to
a. To avoid saturation and provide optimum torque capability
b. 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 constant
d. A var. frequency supply keeping stator flux constant
39. A 3-Ф IM operates at constant rotor frequency when the stator frequency is varied from zero
to rated value. The torque developed by the motor is
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 drives
b. 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 voltage
c. Good harmonic torques
d. Sinusoidal torques
Faculty: 1. Harshpreet Kaur
2. Kavita Jha
Faculty: 1. Harshpreet Kaur
2. Kavita Jha