Electric Drives (3160919) MCQs

MCQs of DC motor characteristics

Showing 51 to 60 out of 71 Questions
51.

The method of speed control of DC Shunt motor is used for applications where a very wide range sensitive speed control is required is

(a)

Ward-Leonard system

(b)

Multiple Voltage Control

(c)

Tapped field control

(d)

Rheostatic Control

Answer:

Option (a)

52.

A dc series motor has an armature resistance of 0.06 Ω and series field resistance of 0.08 Ω. The motor is connected to a 400 V supply. The line current is 20 A when the speed of the machine is 1100 rpm. When the line current is 50 A and the excitation is increased to 30%, the speed of the machine in rpm is

(a)

1100 RPM

(b)

1003 RPM

(c)

837 RPM

(d)

938 RPM

Answer:

Option (c)

53.

Neglecting all losses, the developed torque (T) of a DC separately excited motor, operating under constant terminal voltage, is related to its output power (P) as under:

(a)

T ∝ √P

(b)

T ∝ P

(c)

T is independent of P

(d)

T2 ∝ P3

Answer:

Option (b)

54.

A separately excited DC motor has an armature resistance of 0.5ohm. It runs from a 200 V DC supply drawing an armature current of 20 A at 1500 rpm. For the same field current, the torque developed for an armature current of 10 A will be

(a)

23.59 N-m

(b)

34.76 N-m

(c)

15.28 N-m

(d)

19.99 N-m

Answer:

Option (c)

55.

A 240 V DC series motor takes 40 A when giving its rated output at 1500 rpm. Its resistance is 0.3 Ω. The value of resistance which must be added to obtain rated torque at 1000 rpm is

(a)

(b)

5.7Ω

(c)

2.2Ω

(d)

1.9Ω

Answer:

Option (d)

56.

The deciding factor in the selection of a d.c. motor for a particular application is its ___________ characteristic.

(a)

Speed-Torque

(b)

Speed -Armature current

(c)

Torque -Armature current

(d)

None of the above

Answer:

Option (a)

57.

The direction of rotation of a DC shunt motor can be reversed by interchanging

(a)

The armature terminal only

(b)

Either field or armature terminals

(c)

The supply terminals

(d)

The field terminals only

Answer:

Option (b)

58.

The demand for a large increase in torque of a d.c. shunt motor is met by

(a)

Large decrease in speed

(b)

Large increase in speed

(c)

Large increase in current

(d)

Small increase in current

Answer:

Option (c)

59.

The friction and windage losses in a d.c. motor depends upon ____________

(a)

Speed

(b)

Flux

(c)

Armature current

(d)

Field and armature resistance

Answer:

Option (a)

60.

The iron losses in a d.c. motor depends upon _____________

(a)

Flux only

(b)

Speed only

(c)

Both flux and speed

(d)

None of the above

Answer:

Option (c)

Showing 51 to 60 out of 71 Questions