Majority of the alternators are
(i)single phase(ii)Three phase(iii)Two phase(iv)none of the aboveArmature windings of an alternator are generally
(i)closed windings(ii)open windings(iii)partly open and partly closed windings(iv)none of the aboveThe salient-pole construction for field structure of an alternator is generally used for ______ machine
(i)2-pole(ii)4-pole(iii)8-pole(iv)none of the aboveThe stator of an alternator is identical to that of a _____________
(i)d.c. generator(ii)3-phase induction motor(iii)1-phase induction motor(iv)Rosenberg generatorIn the above question, what is per phase a.c armature resistance?
(i)0.602 Ω(ii)0.452 Ω(iii)0.903 Ω(iv)1.806 ΩThe stator of an alternator rarely uses ______________ slots
(i)wide open type(ii)semi-closed type(iii)closed type(iv)none of the aboveIf the number of poles of an alternator is increased, the generated e.m.f
(i)increases(ii)decreases(iii)remains the same(iv)none of the aboveA two-pole alternator is running at 1500 r.p.m. Its angular velocity is
(i)118 rad/s(ii)192 rad/s(iii)157 rad/s(iv)212 rad/sThe a.c armature winding o f an alternator operates at .................. the field winding.
(i)the same voltage as(ii)much lesser voltage than(iii)much higher voltage than(iv)none of the aboveAn alternator is sometimes called generator.
(i)synchronous(ii)asynchronous(iii)Rosenberg(iv)none of the aboveAn alternator supplying power to a load with a leading power factor always has __________ voltage regulation.
(i)positive(ii)negative(iii)unity(iv)zeroA turbo—alternator uses ____________
(i)salient-pole field structure(ii)non-salient-pole field structure(iii)rotating a.c armature winding(iv)none of the aboveThe non salient-pole field construction is used for alternator.
(i)low-speed(ii)medium-speed(iii)high-speed(iv)none of the aboveWhen the speed of an alternator is reduced by half, the generated e.m.f. will become ___________
(i)twice(ii)one-fourth(iii)half(iv)four timesThe alternators driven by __________ do not have a tendency to hunt.
(i)diesel engines(ii)water turbines(iii)steam turbines(iv)none of the aboveLow-speed alternators are driven by __________
(i)hydraulic turbines(ii)steam engines(iii)steam turbines(iv)none of the aboveIf the excitation of an alternator operating in parallel with other alternators is increased above the normal value of excitation, its ___________
(i)p.f. becomes more lagging(ii)p.f. becomes more leading(iii)output current decreases(iv)output kW decreases.If the excitation of an alternator operating in parallel with other alternators is decreased, its ________________
(i)p.f becomes more leading(ii)p.f becomes more tagging(iii)output kW will change(iv)none of the aboveThe d.c armature resistance of a Y-connected alternator measured across its two terminals is 0.5 Ω. The per phase resistance is __________
(i)0.5 Ω(ii)1 Ω(iii)0.25 Ω(iv)1.5 ΩA 3-phase alternator has 3-slots per pole. The distribution factor of the winding is _____________
(i)0.866(ii)0.5(iii)1(iv)none of the aboveHigh-speed alternators are driven by ____________
(i)diesel engines(ii)hydraulic turbines(iii)steam turbines(iv)none of the aboveThe efficiency of the turbo-alternator ___________ with increase in speed.
(i)decreases(ii)increases(iii)remains unchanged(iv)none of the aboveThe air-gap in an alternator is ___________ in an induction machine.
(i)much shorter than(ii)much longer than(iii)about the same as(iv)none of the aboveThe stator of an alternator is wound for _________ on the rotor.
(i)more number of poles than(ii)less number of poles than(iii)the same number of poles as(iv)none of the aboveTurbo-alternators have rotors of ________
(i)small diameter and long axial length(ii)large diameter and long axial length(iii)large diameter and small axial length(iv)same diameter and axial lengthThe rotor of a turbo-alternator is made cylindrical in order to reduce _______
(i)eddy current loss(ii)hysteresis loss(iii)windage losses(iv)none of the aboveThe number of cycles generated in a 6-pole alternator in one revolution is ___________
(i)3(ii)6(iii)50(iv)none of the aboveThe speed at which a 6-pole alternator should be driven to generate 50 cycles per second is ________
(i)1500 r.p.m(ii)1000 r.p.m(iii)500 r.p.m(iv)none of the aboveThe frequency of e.m.f generated in an 8-pole alternator running at 900 r.p.m is ________
(i)50Hz(ii)60Hz(iii)120 Hz(iv)none of the abovein case of a 4-pole machine, 1 mechanical degree corresponds to __________ electrical degrees.
(i)2(ii)4(iii)8(iv)none of the aboveFor the same rating, the size of low-speed alternator is __________ that of high-speed alternator.
(i)about the same as(ii)more than(iii)less than(iv)none of the aboveThe Synchronous reactance of an alternator is due to
(i)leakage flux(ii)d.c field excitation(iii)armature reaction(iv)none of the aboveThe synchronous reactance of an alternator is generally _________ armature resistance.
(i)5 times smaller than(ii)5 times greater than(iii)10 to too times greater than(iv)10 times smaller thanThe Synchronous reactance of an alternator ___________ as the iron is saturated.
(i)decreases(ii)increases(iii)remains unchanged(iv)none of the aboveIn an alternator, the effect of armature reaction is minimum at power factor of _____________
(i)0.866 lagging(ii)0.866 leading(iii)0.5 lagging(iv)unityIf the lagging load p.f. of an alternator is decreased, the demagnetizing effect of armature reaction ________
(i)remains the same(ii)is decreased(iii)is increased(iv)none of the aboveA 3-phase alternator generates an open-circuit phase voltage of 4000V when exciting current is 50 A ; the short-circuit current for the same excitation being 800 A. The Synchronous reactance per phase is
(i)80 Ω(ii)5 Ω(iii)7.5 Ω(iv)none of the aboveA 30 MVA., 15 kV alternator will have a per phase nominal impedance of ____________
(i)9 Ω(ii)15 Ω(iii)7.5 Ω(iv)none of the aboveWhen toad on an alternator is increased, the terminal voltage increases if the load p.f. is ____________
(i)unity(ii)lagging(iii)leading(iv)zeroThe full-load efficiency of an alternator with the size of the machine.
(i)increases(ii)decreases(iii)remains unchanged(iv)none of the aboveFor the same power rating, an alternator is ____________ that of a d.c generator.
(i)larger in size than(ii)smaller in size than(iii)of the same size as(iv)none of the aboveIn the armature winding of an alternator, the coil span falls short of full-pitch by 60° (electrical). The pitch factor is
(i)0.866(ii)0.5(iii)0.25(iv)none of the aboveThe disadvantage of a short-pitched coil is that _________________
(i)harmonics are introduced(ii)waveform becomes non-sinusoidal(iii)voltage round the coil is reduced(iv)none of the aboveThe voltage regulation of an alternator for a p.f of 0.8 lagging is __________at unity
(i)greater than(ii)smaller than(iii)the same as(iv)none of the aboveThe Voltage regulation of an alternator is larger than that of a d.c generator because of _____________
(i)large armature resistance(ii)large leakage reactance(iii)complex effects of armature reaction(iv)none of the aboveThe per phase d.c. armature resistance of an alternator is 0.5 Ω. The effective a.c armature resistance would be about
(i)0.5 Ω(ii)0.75 Ω(iii)4 Ω(iv)0.25 ΩThe d.c armature resistance of a delta-connected alternator measured across its two terminals is 1 Ω. The per phase d.c resistance is ________________
(i)3 Ω(ii)1.5 Ω(iii)0.33 Ω(iv)none of the aboveAn under-êxcit9d alternator supplies _____________.
(i)lagging VAR(ii)leading VAR(iii)no reactive power(iv)none of the aboveThe distribution of load between two alternators operating in parallel can be changed by changing _____________
(i)phase sequence(ii)field excitation of alternators(iii)driving torques of prime movers(iv)none of the aboveWhen a number of alternators are operating in parallel, the power factor at which each operates is determined by _____________
(i)power factor of the load(ii)driving torque of the prime mover(iii)its field excitation(iv)none of the aboveThe voltage of the bus-bar to which several alternators are paralleled may be raised by simultaneously __________of all alternators.
(i)increasing field excitation(ii)decreasing field excitation(iii)increasing input to prime movers(iv)decreasing input to prime moversThe frequency of the system with which several alternators are paralleled can be increased by simultaneously ______________of all generators.
(i)increasing the field excitation(ii)decreasing the field excitation(iii)increasing the speed of prime movers(iv)decreasing the speed of prime moversDamper windings are used in alternators to ____________
(i)prevent hunting(ii)reduce windage losses(iii)achieve synchronism(iv)none of the aboveThe rating of an alternator is expressed in _____________
(i)kW(ii)H.P.(iii)kVA(iv)kVARA 3-phase, 16-pole alternator has a star-connected winding with 144 slots and 10 conductors per slot. The flux per pole is 30 mWb sinusoidally distributed and the speed is 375 r.p.m. The frequency of generated e.m.f. is ____________
(i)25 Hz(ii)50 Hz(iii)100 Hz(iv)200 HzIn the above question, the line e.m.f. is ____________
(i)1120 V(ii)3750 V(iii)1875 V(iv)2770 VThe magnitude of e.m.f. generated by an alternator depends on ____________
(i)number of poles(ii)rotor speed(iii)flux per pole(iv)all of the aboveVoltage drop in an alternator when under load is due to __________
(i)armature resistance(ii)armature reactance(iii)armature reaction(iv)all of the aboveThe a.c armature winding of an alternator is ______________
(i)always star-connected(ii)generally delta-connected(iii)star-delta connected(iv)none of the aboveFor producing an e.m.f of given frequency, an alternator will run at greatest speed for ____________ poles.
(i)2(ii)4(iii)8(iv)12A 5000 kVA, 1100 V, 50 Hz Y-connected 3-ɸ alternator has armature resistance of 0.1 Ω / phase and synchronous reactance/phase of 1.5 Ω, find the generated e.m.f per phase
(i)769.2 V(ii)832.6 V(iii)692.4 V(iv)935.3 VIn the above question, what is the voltage regulation?
(i)15.6 %(ii)29 %(iii)9.8 %(iv)21.1 %The field winding of an alternator is _____________ excited.
(i)d.c(ii)a.c(iii)both d.c and a.c(iv)none of the aboveA Y-connected 3-ɸ alternator is adjusted to its rated line-to-line voltage of 230 V while under its rated load and at 80% lagging power factor. The same field excitation current results in a no-load line-to-line voltage of 328.6 V. The voltage regulation is
(i)32.7%(ii)21.4%(iii)13.9%(iv)42.8%A Y-connected three-phase alternator is delivering power to a three-phase line. The line-to-line voltage is 460 V. The line currents are 7.73A and the total wattage is 5.12 kW. The load power factor is
(i)72%(ii)83.1%(iii)70.7%(iv)92%If the line-to-line voltage in the above question rises to 618 V at no load with the same excitation, then voltage regulation of the alternator is
(i)34.3%(ii)22.8%(iii)17.4%(iv)41.2%A voltage regulation test is to be performed on a 3-phase Y-connected alternator. Its line-to-line voltage drop is taken with a d.c supply to find its armature circuit resistance. The readings are : d.c voltage drop = 11.15V and line current 18.5A. What is the per phase d.c resistance?
(i)0.602 Ω(ii)0.301 Ω(iii)0.451 Ω(iv)1.22 ΩThe losses in an alternator are the same as in
(i)a d.c machine(ii)a transformer(iii)a rectifier(iv)none of the aboveFor a given load, the efficiency of an alternator is maximum at
(i)0.8 p.f(ii)0.707 p.f(iii)1 p.f(iv)none of the aboveMajority of alternators in the use have _____________
(i)revolving a.c. armature winding(ii)stationary field type construction(iii)revolving field type construction(iv)none of the above.Iron and friction losses of an alternator can be measured by a
(i)transformer(ii)d.c. motor(iii)rectifier(iv)none of the aboveCopper losses of an alternator can be measured by a
(i)rectifier(ii)transformer(iii)d.c. motor(iv)none of the aboveThe voltage regulation of an alternator depends on
(i)load current only(ii)p.f. only(iii)both load current and p.f(iv)none of the above
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Alternators - Multiple Choice Questions
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