## electrical

### Alternator MCQ Questions and Answers Page - 2

1.
 Distributed winding and short chording employed in ac machines will result in A Increase in emf and reduction in harmonics B Reduction in emf and increase in harmonics C Increase in both emf and harmonics D Reduction in both emf and harmonics Answer : D Explanation :
2.
 It is desirable to eliminate 5th harmonic voltage from the phase voltage of an alternator. The coils should be short-pitched by an electrical angle of A 300 B 360 C 720 D 180 Answer : B Explanation :
3.
 The stator of a 3-phase, 6-pole ac machine has 45 slots. The stator winding has 45 coils with a coil span of 6 slots. What type of winding will be selected for this machine? A Double layer fractional slot short pitched winding B Single layer fractional slot short pitched winding C Single layer integral slot full pitch winding D Double layer fractional slot full pitch winding Answer : A Explanation :
4.
 The emf generated due to nth harmonic components of flux in an alternator will be _____the fundamental emf in magnitude A Less than B More than C Equal to D None of these Answer : A Explanation :
5.
 4 pole star connected alternator running at 1500 rpm have 72 slots with 10 conductors per slot. The number of turns per phase and slot angle is A 120 turns and 20 degrees B 100 turns and 10 degrees C 120 turns and 10 degrees D 100 runs and 20 degree Answer : C Explanation :
6.
 Skew of rotor bar eliminates A the effect of space harmonics B the entire effect of crawling C magnetic noise D vibration due to unequal force developed on rotor Answer : A Explanation :
7.
 Harmonics in the emf generated in an alternator can be reduced by A skewing the slots B chamfering the salient pole tips C using distributed winding D all of the above Answer : D Explanation :
8.
 Chording and distribution of armature windings for ac machines results in A Reduction in air gap mmf harmonics B Reduction in fundamental component or induced emf C Increase in fundamental component of induced emf D Both (a) and (b) Answer : D Explanation :
9.
 The short pitch winding is preferred over full pitch winding for an alternator because it A Gives improved waveform of the induced emf as the distorting harmonics can be reduced or totally eliminated B Reduces the inductance of the winding C Increases total induced emf D Both (a) and (b) Answer : D Explanation :
10.
 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 :
11.
 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 :
12.
 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 :
13.
 The stator of modern alternators are wound for _____phase groups A 1800 B 1200 C 600 D 2400 Answer : Select Correct Ans Explanation :
14.
 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 :
15.
 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 :
16.
 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 :
17.
 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 :
18.
 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 :
19.
 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 :
20.
 In a synchronous generator, a divided winding is preferable to a conventional winding rotor because of A Higher efficiency B Increased steady-state stability limit C Higher short-circuit ration D Better damping Answer : B Explanation :
21.
 A 4-pole 3 phase, double layer winding is housed in a 36-slot stator for a ac machine with 600 phase spread. Coil span is 7 slot pitches. Number of slots in which top and bottom layers belong to different phases is A 24 B 18 C 12 D 0 Answer : A Explanation :
22.
 In a cylindrical rotor synchronous machine, the phasor addition of stator and rotor mmfs is possible because A Two mmfs are rotating in opposite directions B Two mmfs are rotating in same direction at different speeds C Two mmfs are stationary with respect to each other D One mmf is stationary and the other mmf is rotating Answer : C Explanation :
23.
 Three phase alternators are invariably connected in star so as to A Reduce the size of stator conductors used B Increase the terminal voltage C Reduce magnetic losses D All of the above Answer : B Explanation :
24.
 The stator winding of an alternator is normally connected in star to eliminate the _____harmonic component of the voltage wave from A Third B Fifth C Seventh D None of these Answer : A Explanation :
25.
 If the dimensions of all of the parts of a synchronous generator and the number of field and armature turns are doubled, then the generated voltage will change by a factor of A 1 B 2 C 4 D 8 Answer : C Explanation :
26.
 The angle between induced emf and terminal voltage on no load for a single-phase alternator is A 1800 B 900 C 00 D None of these Answer : C Explanation :
27.
 The 5th space harmonics in the mmf developed by balanced fundamental frequency armature currents rotate at _____times the synchronous speed with respect to the field A 5/6 B 6/5 C 5/4 D 5/7 Answer : B Explanation :
28.
 When a three-phase alternator supplies capacitive load, armature reaction flux will be A Opposing the main magnetic field B Helping the main magnetic field C Either (a) and (b) D None of the above Answer : B Explanation :
29.
 Fleming’s left-hand rule may be applied to an electric generator to find out direction of A Magnetic field B Induced e.m.f C Rotor rotation D None of the above Answer : B Explanation :
30.
 In an alternator, the armature reaction will be completely magnetizing case the load power factor is A Zero lagging B Zero leading C 0.866 D Unity Answer : B Explanation :
31.
 The dark and bright lamp method is used for A Transfer of load B Synchronizing C Balancing of load D Phase sequence Answer : B Explanation :
32.
 In a synchronous machine, all of the following losses are fixed except A Core loss B Copper loss C Bearing friction loss D Windage loss Answer : B Explanation :
33.
 In a star connected armature winding A Phase voltage contains 3rd harmonic e.m.f but live voltage does not contain it B Phase voltage contains 3rd harmonic e.m.f as live voltage also contains third harmonic components C Phase voltage does not contain third harmonic e.m.f as line voltage also does not contain it D None of the above Answer : A Explanation :
34.
 When the speed of an alternator increases A The frequency decreases B The frequency increases C The frequency remains same D The frequency changes Answer : B Explanation :
35.
 The slip rings employed in a 3-phase alternator in hydro station are insulated for A Low voltage B Very low voltage C Full armature voltage D Extra high-tension voltage Answer : A Explanation :
36.
 An alternator is capable of delivering power at a particular efficiency. The frequency can be increased by A Reversing the armature rotation B Reversing the field polarity C Increasing the current supplied to the field electromagnets D Increasing the armature speed Answer : D Explanation :
37.
 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 Explanation :
38.
 In an alternator, for a coil having a span of 2/3 of pole pitch, the coil span factor will be A 0.866 B 0.707 C 0.6 D 0.2 Answer : A Explanation :
39.
 Excessive windage loss and noise occur with A Cylindrical rotors B Salient pole rotors C Either of the above D None of the above Answer : B Explanation :
40.
 Regulation of an alternator supplying leading load is A Always negative B Always positive C Sometimes positive and sometimes negative depending upon load and power factor D None of the above Answer : C Explanation :
41.
 An infinite bus bar has A Constant frequency and constant voltage B Constant frequency and variable voltage C Variable frequency and variable voltage D Infinite frequency and infinite voltage Answer : A Explanation :
42.
 Which harmonic will be totally eliminated in an alternator by using a fractional pitch of 4/5? A Third B Fifth C Seventh D Ninth Answer : B Explanation :
43.
 Dirt accumulation in generator can cause all of the following except A Low power factor B Poor voltage regulation C Flashover D Overheating Answer : A Explanation :
44.
 If an alternator is operating at leading power factor, then it can be concluded that A The alternator is under-excited B The alternator is over-excited C The torque angle of the alternator has negative value D The residual magnetism of the pole is zero Answer : B Explanation :
45.
 Which fractional pitch will eliminate the seventh harmonic from the voltage waveform of an alternator? A 6/7 B 7/8 C 5/6 D None of this Answer : A Explanation :
46.
 Damper winding on alternator results in all of the following except A Increases instability of machine B Elimination of harmonic effect C Absorption of energy of oscillations when operating in parallel with other alternator D Suppression of spontaneous hunting when supplying power to transmission line with high resistance to reactance ratio Answer : A Explanation :
47.
 In a cylindrical rotor how much portion of the rotor is wound? A One third B   Half C Two third D Full Answer : C Explanation :
48.
 The speed of an alternator is changed from 3000 r.p.m to 1500 r.p.m. the generated e.m.f /phase will become A One fourth B Half C Double D Unchanged Answer : B Explanation :
49.
 Zero power factor method for an alternator is generally used to determine A Synchronous impedance of alternator B Efficiency of an alternator C Voltage regulation of the alternator D None of the above Answer : C Explanation :
50.
 In an alternator the armature reaction is mainly influenced by A The power factor of the load B Short-circuited ratio C Speed of the alternator D Total current drawn Answer : A Explanation :
51.
 Regulation of an alternator supplying resistive or inductive load is A Always negative B Always positive C Either of the above D None of the above Answer : B Explanation :
52.
 4 pole 1500 r.p.m alternator will generate e.m.f at A 20 Hz B 40 Hz C 50 Hz D 60 Hz Answer : C Explanation :
53.
 To obtain sinusoidal flux distribution A Chamfering of poles is done in turbo alternator only B Chamfering of poles is done in salient pole alternators only C Either of the above D None of the above Answer : B Explanation :
54.
 In air-crafts, alternators have operating frequency of A 800 Hz B 400 Hz C 60 Hz D 50 Hz Answer : B Explanation :
55.
 Alternators, now a days are designed to have poor regulation because A It reduces the construction cost B It limits the value of short circuit current C We employ automate voltage regulators D None of the above Answer : B Explanation :
56.
 Voltage regulation of an alternator is usually A Equal to that of power transformer B Much lower than that of a power transformer C Much higher than that of a power transformer D None of the above Answer : C Explanation :
57.
 In an alternator, the stator frame serves A To verticate the armature B To hold the armature stamping C To protect the whole machine D As a return path for the flux Answer : D Explanation :
58.
 For a given output steam turbo-alternator are much smaller is size than water turbine-alternators because A Steam turbo-alternators are built with smaller capacities B Steam turbo-alternators have long rotors C Steam turbo-alternators run at high speed D All of the above Answer : C Explanation :