Multiple Choice Questions on Alternator

 

1. The a.c. the armature winding of an alternator is

A) Delta Star connected.
B) Generally Delta Connected.
C) Star Delta Connected.
D) Always Star connected.

ANSWER= (D) Always Star connected.

 

2. Three-phase alternators are invariably star-connected because

A) Higher terminal voltage is obtained.
B) Less turns of wire are required.
C) Small conductors can be used.
D) Magnetic losses are the minimum.

ANSWER= (A) Higher terminal voltage is obtained.

 

3. Alternators are usually designed to generate

A) Definite currents
B) Definite power factor
C) Variable frequencies
D) Definite frequencies

ANSWER= (D) Definite frequencies

 

4. When the speed of an alternator increases

A) The frequency decrease
B) The frequency increases
C) The frequency remains same
D) The frequency changes

ANSWER= (B) The frequency increases

 

5. In alternators the standard practice, now a days is to have

A) Rotating field
B) Rotating armature
C) Either of the above
D) None of the above

ANSWER= (A) Rotating field

 

6. The pitch factor for a full pitch winding of a synchronous machine is

A) 0
B) 0.5
C) 1
D) 1.5

ANSWER= (C) 1
Explain:- Pitch factor = Winding pitch/Pole pitch, but when winding pitch= pole pitch then pitch factor will be 1.

 

7. In huge alternators, the moving part is

A) Brushes
B) Poles
C) Armature
D) None of the above

ANSWER= (B) Poles

 

8. The frequency of voltage generated in large alternators is

A) 50 Hz
B) 60 Hz
C) In kilo cycles
D) In mega cycles

ANSWER= (A) 50 Hz

 

9. The salient-pole construction for field structure of an alternator is generally used for ________ machine.

A) 2 pole
B) 4 pole
C) 6 pole
D) 8 pole

ANSWER= (D) 8 pole

 

10. A 10 pole AC generator rotates at 1200 rpm. The frequency of AC voltage in cycles per second will be

A) 120 Hz
B) 60 Hz
C) 160 Hz
D) 100 Hz

ANSWER= (D) 100 Hz
Explain:- f= P×N/120; where P=10 poles, N=1200 rpm ,so f=(10×1200)/120= 100 Hz

 

11. In an alternator, pitch factor is the ratio of the e.m.fs. of

A) Full pitch winding to short pitch winding
B) Short pitch coil to full pitch coil
C) Distribute winding to full pitch winding
D) Full pitch winding to concentrated winding

ANSWER= (B) Short pitch coil to full pitch coil

 

12. As the speed of an alternator increases, the frequency

A) Increases
B) Decreases
C) Remains constant
D) May increases or decreases depending on the power factor

ANSWER= (A) Increases

 13. The generator which gives dc supply to the rotor of an alternator is called

A) Convertor
B) Exciter
C) Inverter
D) Rectifier

ANSWER= (B) Exciter

 

 14. The number of electrical degrees passed through in one revolution of a four pole synchronous alternator is

A) 360°
B) 720°
C) 1440°
D) 2880°

ANSWER= (A) 360°

 

15. The rotor of alternator has

A) No slip rings
B) Two slip rings
C) Three slip rings
D) Four slip rings

ANSWER= (B) Two slip rings

 

16. Alternator works on the principle of

A) Self and mutual induction
B) Self mutual induction
C) Faraday’s law of electromagnetic induction
D) Mutual induction

ANSWER= (C) Faraday’s law of electromagnetic induction

 

17. In a rotating electrical machine, the chording angle for eliminating fifth harmonic should be

A) 38°
B) 36°
C) 33°
D) 30°

ANSWER= (B) 36°

 

18. The ratio of armature leakage reactance to synchronous reactance of large size modern alternator is about

A) 0.05
B) 0.2
C) 0.4
D) 0.6

ANSWER= (B) 0.2

 

19. The exciting field coil of an alternator is generally excited by

A) A separate dc generator driver by some source
B) A separate ac generator drive by some source
C) A dc generator coupled directly to the armature shaft
D) A battery

ANSWER= (C) A dc generator coupled directly to the armature shaft

 

20. The material used for the manufacture of large turbo-alternator is

A) Cold rolled grain oriented steel
B) Hot rolled grain oriented steel
C) Wrought iron
D) Cast steel

ANSWER= (C) Wrought iron