## electrician

### MCQ ON ALTERNATOR PAGE - 1

1.
 A 4-pole, 50 Hz alternator will have a rotational speed of A 750 rpm B 1500 rpm C 3000 rpm D 1440 rpm Answer : B Explanation :
2.
 An exciter used for field excitation of an alternator will be a A Series generator B Shunt generator C Series motor D Shunt motor Answer : B Explanation :
3.
 The reason of using laminated cores in the stator of an alternator is to A Reduce the weight of the machine B Reduce the eddy current loss C Increase the magnetic flux D Increase the eddy current loose Answer : B Explanation :
4.
 D.C and A.C generators are similar in one important respect that is: A The generated e.m.f is D.C B The generated e.m.f is pulsating C The generated emf is A.C D The generated emf is oscillating Answer : C Explanation :
5.
 An 8- pole alternator rotates at 750 rpm it per cycle periodic time will be: A 10 ms B 20 ms C 30 ms D 50 ms Answer : B Explanation :
6.
 Alternators designed to be driven by steam turbines are built for: A High-speed operation B Low speed operation C Medium speed operation D Both low and medium speed operations Answer : A Explanation :
7.
 Single-phase portable generators are generally made in the range of : A 5000 kVA B 1000kVA C 100 kVA D 5kVA Answer : D Explanation :
8.
 An alternator supplied electric power to various kinds of loads of a factory. If the phase sequence of the alternator is changed, it will affect the A 3-phase heating circuits B 3-phase motor circuits C Single-phase motor circuits D Lighting circuits Answer : B Explanation :
9.
 The values of pitch factor and distribution factor for an alternator are 0.9 and 0.8 respectively. This will develop an e.m.f lesser than an alternator having full pitch coil and concentrated windi A 0.7 B 0.72 C 0.88 D 0.92 Answer : B Explanation :
10.
 The winding of a 4-pole alternator is having 36 slots and a coil span of 1 to 8. It is short pitched by …. Electrical degrees. A 80 B 40 C 20 D 10 Answer : B Explanation :
11.
 The number of slip rings used in a 3 phase, star connected alternator having a rotating armature will be: A 2 B 4 C 3 D 6 Answer : C Explanation :
12.
 The pitch factor is defined as the ratio of the e.m.f of the A Full  pitch winding to short-pitch winding B Short pitch coil to full pitch coil C Full pitch winding to concentrated winding D Distributed winding to full pitch winding Answer : B Explanation :
13.
 The rotor of a salient pole alternator has 12 poles. The number of cycle of e.m.f in one revolution will be A 2 B 6 C 4 D 8 Answer : C Explanation :
14.
 In large-sized alternator, dampers are used to A Reduce current fluctuations B Reduce current fluctuations C Increase stability D Increase output emf Answer : C Explanation :
15.
 The number of electrical degrees which passes through in one revolution of a 6-pole alternator is A 21600 B 10800 C 7200 D 3600 Answer : B Explanation :
16.
 The waveform of the e.m.f generated by an alternator should be : A Pulse shaped wave B Square wave C Sine wave D Triangular wave Answer : C Explanation :
17.
 The field circuit of a hydro alternator is supplied with A an a.c B a pulsating current C an oscillating current D a d.c Answer : D Explanation :
18.
 when a coil/conductor moves at right angle to the magnetic flux, the induced e.m.f will be A lagging B leading C maximum D Zero Answer : C Explanation :
19.
 salient pole type rotors as compared to the cylindrical pole type rotors are A smaller in diameter and larger n axial length B larger in diameter and smaller in axial length C larger in diameter and axial length D smaller in diameter and axial length Answer : B Explanation :
20.
 The frequency generated by a 8-pole alternator rotating at 600 r.p.m. will be A 20Hz B 40Hz C 60Hz D 80Hz Answer : B Explanation :
21.
 The frequency of voltage generated by an altenator having 4 poles and rotating at 1800 R.P.M is A 60 Hz B 7200 Hz C 120 Hz D 450 Hz Answer : A Explanation :
22.
 A 50 Hz alternator will run at the greatest possible speed if it is wound for …. poles A 8 B 6 C 4 D 2 Answer : D Explanation :
23.
 When Speed of an alternator is changed from 3600 R.P.M to 1800 R.P.M, the generated e.m.f per phase will become A One –half B Twice C Four times D One-fourth Answer : A Explanation :
24.
 The power factor of an alternator is determined by its A Speed B Load C Excitation D Prime mover Answer : B Explanation :
25.
 For proper parallel operation, polyphase alternators must have the same A kVA rating B voltage rating C speed D excitation Answer : B Explanation :
26.
 The number of poles in turbo alternator is A 2 B 6 C 8 D 10 Answer : A Explanation :
27.
 The frequency of e.m.f generated by an alternator depends upon the speed N and No. of poles is given by A PN/60 B 60N/P C PN/120 D 120N/P Answer : C Explanation :
28.
 The current from the stator of an alternator is taken out to the external load circuit through A Slip rings B Commutator segments C Solid connections D Carbon brushes Answer : C Explanation :
29.
 In a synchronous machine, the stator frame is made of A Stainless steel B Aluminum C Cast iron or welded steel plates D Laminated silicon steel Answer : C Explanation :
30.
 The stator of an alternator gets overheated due to A Open phase B Unbalanced currents in the phases C Improper alignment of the rotor D Any one or more of the above Answer : D Explanation :