 ## electrical

### Alternator MCQ Objective Questions and Answers Page - 2

1.
 in a salient pole synchronous machine, the air gap is A uniform under the whole pole shoe B least under the middle of the pole she and increases outwards C largest under the middle of the pole shoe  and decreases outwards D least at one end of the pole shoe and increases to the maximum value at the other end. Answer : Select Correct Ans Explanation :
2.
 The number of poles on turbo alternator is usually A 2 B 4 C 6 D 8 Answer : Select Correct Ans Explanation :
3.
 To obtain sinusoidal flux  distribution, chamfering of poles is done in A Salient pole alternators only B Smooth cylindrical pole alternators only C Both of the above D none of the above Answer : Select Correct Ans Explanation :
4.
 the salient pole rotors are  not suitable for high speed turbo generators due to A excessive  bearing  friction B undesirable mechanical oscillations C high centrifugal force and windage loss D large eddy current losses Answer : Select Correct Ans Explanation :
5.
 in turbo alternators smooth cylindrical rotors have very long axial length because it A  reduces friction and windage loss B Reduces  centrifugal force C Number of conductors being less they have to be necessarily long for generating the required volt D None of the above Answer : Select Correct Ans Explanation :
6.
 Cylindrical rotor alternators use ____ducts  for efficient cooling A Only radial B Only axial C Both radial and axial D None of the above Answer : Select Correct Ans Explanation :
7.
 In cylindrical rotor ____portion of rotor is wound A One –third B Two third C One half D Whole Answer : Select Correct Ans Explanation :
8.
 The maximum possible speed at which an alternator can be driven to generate 50 Hz and 4,000 V is A 4,000 rpm B 3,600 rpm C 3,000 rpm D 1,500 rpm Answer : Select Correct Ans Explanation :
9.
 Two mechanically coupled alternators deliver power at 50Hz and 60 Hz respectively .  The highest  speed of the alternator si A 3,600 rpm B 3,000 rpm C 600 rpm D 500 rpm Answer : Select Correct Ans Explanation :
10.
 The most appropriate operating  speeds in rpm of generators used in Thermal, Nuclear and Hydropower plants would respectively be A 3000, 300 and 1500 B 3000,3000 and 300 C 1500,1500 and 3000 D 1000,900 and 750 Answer : Select Correct Ans Explanation :
11.
 The aircraft alternators are designed  to generate emf of high frequency of 400 Hz in order to A Reduce the bulk B Compensate for high speeds C  Make the systems free from external disturbances D All of the above Answer : Select Correct Ans Explanation :
12.
 Armature winding is one in which A Emf is induced by the leakage flux B Emf is induced by the main or working flux C Working or main flux is created by the filed current D Working or main flux is created b y the armature current. Answer : Select Correct Ans Explanation :
13.
 Armature winding in ac machines A Is always closed one B Is always open one C May be either closed one giving delta connections of open one giving  star connections D Answer : Select Correct Ans Explanation :
14.
 The stator of modern alternators are wound for _____phase groups A 1800 B 1200 C 600 D 2400 Answer : Select Correct Ans Explanation :
15.
 Concentrated winding has A  One coil per phase B Two coils per phase C One coil per pair of poles per phase D One coil side per pole pair per phase Answer : Select Correct Ans Explanation :
16.
 For a two layer winding the number of stator slots is equal to the number of A Poles B Conductors C Coil sides D Coils Answer : Select Correct Ans Explanation :
17.
 for a concentrated winding  the polar group of each phase is ____electrical degrees part A 360 B 180 C 120 D 60 Answer : Select Correct Ans Explanation :
18.
 Distributed winding is preferred over concentrated winding as it A Reduces noise B Reduces the machine size C Reduces the amount of copper required D Improves the generated emf waveform and adds rigidity and mechanical strength to the winding Answer : Select Correct Ans Explanation :
19.
 In a synchronous alternator, which of the following coils will have emf closer to sine wave form A Concentrated winding in full pitch coils B Concentrated winding in short pitch coils C Distributed winding in full pitch coils D Distributed winding in short pitch coils Answer : Select Correct Ans Explanation :
20.
 If the space flux distribution is non sinusoidal , emf induced in the distributed winding will be A More sinusoidal in comparison to the flux distribution B Less sinusoidal in comparison to the flux distribution C Of the same shape as that of flux distribution D None of the above Answer : Select Correct Ans Explanation :