## electrical

### Alternator MCQ Questions and Answers Page - 4

1.
 A leading pf load on an alternator implies that its voltage regulation shall be A Positive B Negative C Zero D Any one of these Answer : D Explanation :
2.
 The effect of leading power factor on the voltage regulation of an alternator is A Increasing in nature B Decreasing in nature C Maintained at constant value D Oscillating in nature Answer : B Explanation :
3.
 The leakage reactance of a three-phase alternator is determined by performing A Open circuit ad zero power factor tests B Zero power factor and slip tests C Open and short circuit tests D Short circuit and slip tests Answer : A Explanation :
4.
 The synchronous impedance method of finding the voltage regulation of a cylindrical rotor alternator is generally considered as A A pessimistic method because saturation is not considered B An optimistic method because saturation is not considered C A fairly accurate method even if power factor is not taken into account while determining synchronous impedance D A fairly accurate method when power factor is taken into account while determining synchronous impedance Answer : A Explanation :
5.
 The regulation obtained by synchronous impedance method is always higher than actual value because A Synchronous reactance is assumed variable while it is not B Effective armature resistance is assumed constant C Synchronous reactance is assumed constant while it is not. D Field current is increased to give short circuit current about twice of full load current. Answer : C Explanation :
6.
 The short circuit characteristics of an alternator is A Always linear B Always nonlinear C Either of (a) and (b) D None of these Answer : A Explanation :
7.
 Under short –circuit conditions, the power factor of an alternator is A Unity B Almost zero lagging C Almost zero leading D None of the above Answer : B Explanation :
8.
 The zero-power factor characteristic for the Potier diagram can be obtained by loading the alternator using A Lamp load B Synchronous motor C Water load D Dc motor Answer : B Explanation :
9.
 Modern alternators are designed to have poor regulation as it A Increases the value of short circuit current B Limits the value of short circuit current C Increases the efficiency of operation D Both (a) and (c) Answer : B Explanation :
10.
 Armature reaction mmf and leakage reactance of a synchronous machine are determined by A Open circuit and short circuit tests B Open circuit and zero pf tests C Open circuit test only D Zero pf test only Answer : B Explanation :
11.
 Which one of the following methods would give higher than actual value of regulation of an alternator? A ZPF method B MMF method C EMF method D ASA method Answer : C Explanation :
12.
 Which one of the following methods gives more accurate result for determination of voltage regulation of an alternator? A MMF method B Synchronous impedance method C Potier triangle method D American institution standard method Answer : C Explanation :
13.
 Slip test is performed to determined A Slip B Direct axis reactance and quadrature axis reactance C Positive sequence reactance and negative sequence reactance D Sub transient reactance Answer : B Explanation :
14.
 For maximum current during slip test on a synchronous machine the armature mmf align along A D-axis B Q-axis C 450 to d-axis D 450 to q-axis Answer : B Explanation :
15.
 In which one of the following is reluctance power developed? A Salient pole alternator B Non salient pole alternator C Squirrel cage induction motor D Transformer Answer : A Explanation :
16.
 Which is the value of load angle when the power output of a salient pole synchronous generator is maximum? A 00 B 450 C 900 D None of the above Answer : D Explanation :
17.
 An alternator with higher value of SCR has A Poor voltage regulation and lower stability limit B Better voltage regulation and higher stability limit C Poor voltage regulation and higher stability limit D Better voltage regulation and low stability limit Answer : B Explanation :
18.
 If the excitation of a 3-phase alternator operating on infinite bus bars is changed, which one of the following shall alter? A Active power of machine B Reactive power of machine C Terminal voltage of machine D Frequency of machine Answer : B Explanation :
19.
 A 3-phase synchronous generator with constant steam input supplied power to an infinite bus at a lagging power factor. If the excitation is increased A Both power angle and power factor decrease B Both power angle and power factor increase C The power angle decreases while power factor increases D The power angle increases while power factor decreases Answer : A Explanation :
20.
 A turbo alternator set feeds power to a 3-phase constant voltage constant frequency bus. If the steam supply to the set is cut off, then the set will A Continue to run at rated speed in the same direction B Continue to run at a reduced speed in the same direction C Run at rated speed in the reverse direction D Come to stop Answer : A Explanation :
21.
 The mmf produced by single phase winding is A Pulsating and rotating with constant speed B Pulsating and stationary C Constant in amplitude and stationery D Constant in amplitude and rotating Answer : B Explanation :
22.
 A polyphase field is A Pulsating and stationary B Pulsating and rotating C Constant in amplitude and rotating at synchronous speed D Constant in amplitude and stationary in space Answer : C Explanation :
23.
 A synchronous generator has its field winding on the rotor and armature winding on the stator. When running under steady state conditions its air gap field is A Stationary with respect to stator B Rotating at synchronous speed with respect to rotor C Rotating at synchronous speed against the direction of rotor rotation D Rotating at synchronous speed in the direction of rotor rotation Answer : D Explanation :
24.
 The load between two steam-driven alternators operating in parallel may be adjusted by varying A Steam supply to their prime mover B Speed of the alternators C Field strength of the alternators D Power factor of the alternators Answer : A Explanation :
25.
 Overheating of generator’s winding A Reduces life of the machine B Does not have any significant effect C Reduces generated voltage D Reduces power factor Answer : A Explanation :
26.
 The maximum current that can be supplied by an alternator depends on A Exciter current B Strength of the magnetic field C Number of poles D Speed of the exciter Answer : D Explanation :
27.
 The regulation of an alternator is likely to be negative in case of A Lagging power factor of the load B Leading power factor of the load C The variations of terminal voltage under the condition of maximum and minimum excitation D None of the above Answer : B Explanation :
28.
 The regulation of an alternators is A The increase in internal voltage when load is thrown off B The reduction in terminal voltage when alternator is loaded C The variation of terminal voltage under the condition of maximum and minimum excitation D The change in terminal voltage from lagging power factor to leading power factor Answer : A Explanation :
29.
 An alternator is said to be over excited when it is operating at A Lagging power factor B Leading power factor C Unity power factor D Lagging to leading power factor Answer : B Explanation :
30.
 An alternator driven by francies hydraulic turbine is a ……………. Alternators A Low speed B Medium speed C High speed D Low or medium speed Answer : D Explanation :
31.
 If two alternators are running in proper synchronous are running in proper synchronism and the voltage of one machine is suddenly increased A Both machine will stop B One machine will stop C Synchronizing torque will be produced to restore further synchronism D None of the above Answer : C Explanation :
32.
 The power factor of an alternator is determined by its A Excitation B Speed C Prime mover D Load Answer : D Explanation :
33.
 Two alternators are to be put in parallel. Which of the following factor should be identical for both A Frequency B Phase sequence C Voltage D All of the above Answer : D Explanation :
34.
 If the steam supply of an alternator running in parallel with another identical alternator is increased keeping its excitation constant then. A It will supply greater portion of the load B The power factor would be decreased C It would over-run the other alternator D Its rotor will fall back in phase with respect to the other machine Answer : A Explanation :
35.
 An exciter for a generator is a A Shunt motor B Series motor C Series generator D Shunt generator Answer : C Explanation :
36.
 Two alternators ‘1’ and “2” are sharing an inductive load equally. If the excitation of alternator ‘1’ is increased A Alternator ‘2’ will deliver less current and alternator ‘1’ will deliver more current B Alternator ‘2’ will deliver more current and alternator ‘1’ will deliver less current C Both will deliver more current D Both will continue to share load equally Answer : A Explanation :
37.
 Which of the following coils in an alternator will have e.m.f closer to sine waveform? A Distributed winding in full pitch coil B Distributed winding in short pitch coils C Concentrated winding in full pitch coils D Concentrated winding in short pitch coil Answer : B Explanation :
38.
 The distribution factor, in alternators is defined as the ratio e.m.f of A Distributed winding to full pitch winding B Concentrated winding to distributed winding C Distributed winding to concentrated winding D Full pitch winding to distributed winding Answer : C Explanation :
39.
 As load power factor of an alternator becomes more leading, the value of generated voltage required to give rated terminal voltage A Decreases B Increase C Varies with rotor speed D Remains unchanged Answer : A Explanation :
40.
 In an alternator, the flux created by the armature m.m.f subtracts directly from the main flux for the following conditions of load A Load power factor is unity B Load power factor is 0.6 lagging C Load power factor is zero lagging D Load power factor is zero leading Answer : C Explanation :
41.
 Synchronous impedance method of finding voltage regulation of an alternators is called pessimistic method because A It is simplest to perform and compute B It gives regulation value higher than is actually found by direct loading C Armature reaction is wholly magnetizing D None of the above Answer : B Explanation :
42.
 In a synchronous machine, if the field flux axis is ahead of the armature field axis, in the direction of rotation the machine is working as A Synchronous generator B Asynchronous generator C Synchronous motor D Asynchronous motor Answer : A Explanation :
43.
 In a synchronous machine, if the field flux axis is ahead of the armature field axis, in the direction of rotation, the machine is working as A Synchronous generator B Asynchronous generator C Synchronous motor D Asynchronous motor Answer : A Explanation :
44.
 The advantage of salient pole in an alternator is A Reduced windage loss B Reduce bearing loads and noise C Reduced noise D Adaptability of low and medium speed operation Answer : D Explanation :
45.
 For parallel operation of the two alternator, desirable feature is that both should have A Same reactance B Same resistance C More of resistance as compared to synchronous reactance D Less of resistance as compared to synchronous reactance Answer : D Explanation :
46.
 If two alternators are running in parallel and excitation of one of the alternators is increased, then A Power output will decrease B Wattles component will change C Machine with excess excitation will burn D Both machine will start vibrating Answer : B Explanation :
47.
 When an alternator is supplying unity power factor load, the armature reaction will produce A Distortion of the main field B Magnetization of the main field C Demagnetization of the main field D None of the above Answer : A Explanation :
48.
 If the driving force of both the alternators running in parallel is changed, this will result in change in A Generated voltage B Frequency C Back e.m.f D All of the above Answer : B Explanation :
49.
 In an alternator, when the load power factor is unity A The armature flux will be demagnetising B The armature flux will be cross magnetising C The armature flux will reduce to zero D The armature flux will have square wave form Answer : B Explanation :
50.
 The potier’s triangle separates the A Stator voltage and rotor voltage B Field m.m.f and armature m.m.f C Armature leakage reaction and armature reaction m.m.f D Iron losses and copper losses Answer : C Explanation :
51.
 In an alternator zero power factor method is used to find the A Synchronous Impedance B Efficiency C Armature resistance D Voltage regulation Answer : D Explanation :
52.
 If the driving power from the prime from the prime mover driving an alternator is lost but the alternator remains connected to the supply network and field supply network and field supply is on then the alternator will A Behave as an induction motor but will rotate in an opposite direction B Behave as a synchronous motor and will rotate in the same direction C  Get burnt D None of the above Answer : B Explanation :
53.
 In turbo-alternators, smooth cylindrical type rotor used have long axial length because A It gives smooth running of the roto B It reduces windage loss C Centrifugal force is reduced D Number of armature conductor held in the large circumference rotor being large, they need not be long Answer : D Explanation :
54.
 Which of the following methods used for synchronizing of 3-phsae synchronous generator is considered best one? A Three dark lamp method B Two bright and one dark lamp method C Synchroscope D None of these Answer : C Explanation :