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Electrician 3rd sem DC Motor

Total questions: 67

Worksheet time: 34mins

Name
Class
Date
1.

Which instrument is used to measure armature winding resistance?

a)

Megger

b)

Multimeter

c)

Series type Ohm meter

d)

Kelvin bridge

2.

Which instrument is used to test armature winding for short and open circuit?

a)

Tong Tester

b)

Internal Growler

c)

External Growler

d)

Digital multimeter

3.

What is the name of the speed control method of DC motor?

a)

Field diverter method

b)

Field tapping method

c)

Voltage control method

d)

Armature diverter method

4.

Which winding wire is used for DC field coil?

a)

Super enamelled copper wire

b)

Single silk covered copper wire

c)

Double silk covered copper wire

d)

PVC covered copper winding wire

5.

Which formula is used to calculate the speed of DC motor?

a)

N=EbΦN=\frac{E_b}{\Phi}

b)

N=ΦEbN=\frac{\Phi}{E_b}

c)

N=Eb.Φ 120N=\frac{E_b.\Phi\ }{120}

d)

N=EbΦ60N=\frac{E_b\Phi}{60}

6.

How many parallel paths in duplex lap winding in the armature of 4 pole D.C Motor?

a)

2

b)

4

c)

6

d)

8

7.

Which rule determines the direction of rotation of armature in D.C motor?

a)

Right hand grip rulee

b)

Right hand palm rule

c)

Fleming’s left hand rule

d)

Fleming’s right hand rule

8.

What is the name of D.C motor?

a)

D.C shunt motor

b)

D.C series motor

c)

D.C differential compound motor

d)

D.C cumulative compound motor

9.

Which rule determines the direction of current in D.C motor?

a)

Right hand grip rule

b)

Right hand palm rule

c)

Fleming’s left hand rule

d)

Fleming’s right hand rule

10.

What is the formula to calculate the current taken by D.C shunt motor armature?

a)

Ia=VRaI_a=\frac{V}{R_a}

b)

Ia=EbRaI_a=\frac{E_b}{R_a}

c)

Ia=V−EbRaI_a=\frac{V-E_b}{R_a}

d)

Ia=V+EbRaI_a=\frac{V+E_b}{R_a}

11.

Which rule is applied to identify the direction of flux in DC motor?

a)

Cork’s screw rule

b)

Right hand grip rule

c)

Fleming’s left hand rule

d)

Fleming’s right hand rule

12.

Name the type of DC motor.

a)

Shunt motor

b)

Series motor

c)

Long shunt compound motor

d)

Short shunt compound motor

13.

What is the formula to calculate back EMF in a DC motor?

a)

Eb=ZNPΦ60AE_b=\frac{ZNP}{\Phi60A}

b)

Eb=NPZΦ60AE_b=\frac{NP}{Z\Phi60A}

c)

Eb=ΦZNP60AE_b=\frac{\Phi ZNP}{60A}

d)

Eb=60AΦZNPE_b=\frac{60A\Phi}{ZNP}

14.

What is the name of the equipment?

a)

Megger

b)

Earth resistance tester

c)

Internal growler

d)

External growler

15.

What is the name of winding, if coil pitch is less than pole pitch?

a)

Full pitch winding

b)

Half pitch winding

c)

Long chorded winding

d)

Short chorded winding

16.

What is the purpose of series resistor connected with holding coil in a D.C four point starter?

a)

Limit the current in holding coil

b)

Increase the current in holding coil

c)

Increase the voltage in holding coil

d)

Decrease the voltage in holding coil

17.

Which speed control method of D.C series motor is used for electric train?

a)

Field diverter method

b)

Field tapping method

c)

Armature diverter method

d)

Supply voltage control method

18.

Why shunt field coil is connected in series with holding coil in D.C three point starter?

a)

Increase the holding coil current

b)

Decrease the holding coil current

c)

Protect the shunt field from over current

d)

Protect the motor in case of open in shunt field

19.

Why the direction of rotation is changed only by changing the armature current direction in a D.C compound motor?

a)

Maintain rated speed

b)

Maintain motor characteristics

c)

Avoid armature reaction effect

d)

Prevent motor from over loading

20.

Which speed control methods offers below normal speed in DC shunt motor?

a)

Field control method

b)

Voltage control method

c)

Armature control method

d)

Ward Leonard system of speed control

21.

Why starters are required to start D.C motors in industries?

a)

Regulate the field voltage

b)

Reduce the armature current

c)

Control the armature reaction

d)

Smooth operation of motors

22.

Which insulating material belongs to class ‘B’ insulation?

a)

Cotton

b)

Bamboo

c)

Fiber glass

d)

Leatheroid paper

23.

What is the temperature value of class ‘F’ insulation?

a)

90°C

b)

105°C

c)

120°C

d)

155°C

24.

Which type of D.C motor is used for constant speed drives?

a)

DC series motor

b)

DC shunt motor

c)

Differential long shunt compound motor

d)

Differential short shunt compound motor

25.

Which type of DC motor is used in elevators?

a)

DC series motor

b)

DC shunt motor

c)

DC differential compound motor

d)

DC cumulative compound motor

26.

Which method of speed control gives below the rated speed in DC series motor?

a)

Field diverter method

b)

Tapped field method

c)

Voltage control method

d)

Armature diverter method

27.

What is the effect, if a four point starter resistance is cutoff during running?

a)

Motor stopped

b)

Runs at slow speed

c)

Runs at very high speed

d)

Runs at reverse direction

28.

Why carbon composition brush requires in the armature circuit to operate the D.C motor?

a)

Increases the starting torque

b)

Protects from armature reaction

c)

Protects armature from over loading

d)

Reduces the spark in the commutator segment

29.

Why series motor produce high torque and speed initially without load?

a)

Absence of back emf

b)

Load current flows through field winding

c)

Armature current and field current are same

d)

Series field winding wound with thick wire

30.

Why the series field is short circuited at the time of starting in differential compound motor?

a)

To reduce the starting current

b)

To increase the speed of motor

c)

To decrease the speed of motor

d)

To maintain proper direction of rotation

31.

Which is the most effective method of balancing armature?

a)

Static balancing

b)

Dynamic balancing

c)

Attached with counter balancing

d)

Plugged with lead weight balancing

32.

Which material is used for starting resistance of DC starters?

a)

Eureka

b)

Nichrome

c)

Manganin

d)

Constantine

33.

Which DC compound motor is operated at constant speed under varying load?

a)

Differential long shunt

b)

Cumulative long shunt

c)

Differential short shunt

d)

Cumulative short shunt

34.

How No volt coil is connected in a three point starter with DC shunt motor?

a)

Directly connected to supply

b)

Connected in series with armature

c)

Connected in parallel with armature

d)

Connected in series with shunt field

35.

Which type of armature winding is illustrated?

a)

Duplex lap winding

b)

Triplex lap winding

c)

Simplex lap winding

d)

Quadruplex lap winding

36.

Which growler test for armature is illustrated?

a)

Open coil test

b)

Grounded coil test

c)

Shorted coil test

d)

Shorted commutator test

37.

Which speed control method is applied to obtain both below normal and above normal speed in DC motor?

a)

Field control method

b)

Armature control method

c)

Tapped field speed control

d)

Tapped field speed control

38.

Why commutators are sparking heavily?

a)

Incorrect brush position

b)

Incorrect field connectionn

c)

Incorrect direction of rotation

d)

Incorrect armature connection

39.

What is the action of the induced emf in a running D.C motor?

a)

Assists the applied voltage

b)

Opposes the applied voltage

c)

Increases the armature current

d)

Decreases the armature current

40.

Which motor has this characteristics curve?

a)

Series motor

b)

Shunt motor

c)

Cumulative compound motor

d)

Differential compound motor

41.

What is the purpose of resistor connected with holding coil in 4 point starter?

a)

Limit current in NVC

b)

Protect the coil from short circuit

c)

Protect the motor from overload

d)

Protect the armature from short circuit

42.

Why the D.C series motor field winding is wound with thick wire?

a)

To regulate field voltage

b)

To carry the load current

c)

To keep maximum inductance

d)

To reduce the armature reaction

43.

Which type of speed control of D.C series motor?

a)

Field parallel method

b)

Field diverter method

c)

Field tapping method

d)

Armature diverter method

44.

Which type of D.C motor is suitable for shearing machines?

a)

Shunt motor

b)

Series motor

c)

Cumulative compound motor

d)

Differential compound motor

45.

Where D.C compound motors are preferred?

a)

Constant load requirements

b)

tant speed requirements

c)

High starting torque requirements

d)

Constant speed under varying load requirements

46.

What is the necessity of starter for D.C motor?

a)

Limit the field current

b)

Limit the field voltage

c)

Control the motor speed

d)

Limit the armature current

47.

Which type of instrument is used to test the armature winding?

a)

Megger

b)

Growler

c)

Multimeter

d)

Ohmmeter

48.

Why the holding coil of a 3 point starter is connected in series with shunt field?

a)

To limit the load current

b)

To run motor at low voltage

c)

To hold the handle plunger firmly

d)

To protect the motor from high speed

49.

What is the best method to change the DOR of a compound motor without change of its characteristics?

a)

Change armature current direction

b)

Change shunt field current direction

c)

Change series field current direction

d)

Change the current in armature and shunt field together

50.

What is the purpose of NVC connected in series with the field in 3 point starter?

a)

To improve the torque

b)

Reduce the field current

c)

To decrease the back emf

d)

To prevent increase in speed

51.

Which type of DC motor is used for sudden application of heavy loads?

a)

Shunt motor

b)

Series motor

c)

Differential compound motor

d)

Cumulative compound motor

52.

Which speed control method is used in food mixture motors?

a)

Voltage control method

b)

Field diverter control method

c)

Armature diverter method

d)

Series field tapping method

53.

Which speed control system provides a smooth variation of speed from zero to above normal?

a)

Field control

b)

Armature control

c)

Field diverter control

d)

Ward-Leonard system control

54.

What is the purpose of tapes in winding?

a)

Insulate slots

b)

Bind the coils

c)

Wrap the conductor

d)

Insulate exposed conductors

55.

Which type of DC armature winding the front pitch (YF) is greater than back pitch (YB)?

a)

Lap winding

b)

Wave winding

c)

Progressive winding

d)

Retrogressive winding

56.

What reduces the cross sectional area of core material for VA rating?

a)

Dynamo sheet

b)

Low alloy sheet

c)

High alloy sheet

d)

Normal steel sheet

57.

How to obtain opposite polarity in adjacent poles of a 4 pole DC motor?

a)

Varying the number of turns in coil

b)

Making series connection of

c)

Making parallel connection of coils

d)

Making current flow in different direction

58.

What is the operation in the rewinding process?

a)

Cleaning of slots

b)

Removing of winding

c)

Removing of wedges

d)

Cutting of winding wire

59.

Which insulating material used in winding is a highly non -hygroscopic and possess good electrical strength?

a)

Empire cloth

b)

Triplex pape

c)

Millinex paper

d)

Leatheroid paper

60.

Which type of armature winding is illustrated?

a)

Triplex wave winding

b)

Duplex wave winding

c)

Progressive lap winding

d)

Retrogressive lap winding

61.

Calculate the average pitch (YA) for retrogressive wave winding, if No. of armature conductor = 14, No. of slots = 7, No. of poles = 2

a)

4

b)

6

c)

8

d)

14

62.

Which type of test is illustrated for the armature after rewound?

a)

Open coil test

b)

Shorted coil test

c)

Voltage drop test

d)

Grounded coil test

63.

Why the newly rewound armature must be preheated before varnishing?

a)

Drive out the moisture from it

b)

Help for quick drying of varnish

c)

Make easy to penetrate varnish inside

d)

Maintain uniform spreading of varnishing

64.

How the direction of rotation of a DC compound motor is changed?

a)

By changing the direction of armature current

b)

By interchanging the supply terminals

c)

By changing the direction of both field and armature current

d)

By changing the direction of series field current

65.

What is the effect in a D.C shunt motor, if its supply terminals are interchanged?

a)

Runs in slow speed

b)

Runs in high speed

c)

Runs in the same direction

d)

Runs in the reverse direction

66.

What is the speed, if field winding of a DC shunt motor is in open circuit?

a)

Stop running

b)

Motor runs normally

c)

Runs at slow speed

d)

Runs in very high speed

67.

What is the reason for reduction in speed of a D.C shunt motor from no load to full load?

a)

Shunt field current increases

b)

Shunt field current decreases

c)

Armature voltage drop increases

d)

Armature voltage drop decreases

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