MCQ in AC Generators Part 1 | REE Board Exam

This is the Multiple Choice Questions Part 1 of the Series in AC Generators as one of the Electrical Engineering topic. In Preparation for the REE Board Exam make sure to expose yourself and familiarize in each and every questions compiled here taken from various sources including but not limited to past Board Exam Questions in Electrical Engineering field, Electrical Engineering Books, Journals and other Electrical Engineering References.

Start Practice Exam Test Questions Part 1 of the Series

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1.  EE Board Exam October 1990

What is the speed of a 100 kW, 230-volt, three-phase, four-pole, 60 Hz alternator?

A.  450 rpm

B.  900 rpm

C.  1200 rpm

D.  1800 rpm

2.  REE Board Exam April 1997

A six-pole, 3-phase AC generator has 72 slots, the coil span is 12. What is the pitch factor?

A.  1.000

B.  0.939

C.  0.985

D.  0.966

3.  REE Board Exam October 1994

A 30 MVA, 15 kV three-phase alternator will have a per phase nominal impedance of ______.

A.  7.5 ohms

B.  9 ohms

C.  15 ohms

D.  none of these

4.  EE Board Exam April 1990

A 6-pole, 3-phase, 60 cycle alternator has 12 slots per pole and four conductors per slot. The winding is 5/6 pitch. There are 2,500,000 Maxwells entering the armature from each North Pole, and this flux is sinusoidally distributed along the air gap. The armature coils are all-connected in series. The winding is wye-connected. Determine the open circuit emf of the alternator.

A.  532.1 V

B.  504.2 V

C.  512.4 V

D.  572.4 V

5.  EE Board Exam April 1995

A 1200 kVA, 6600 volt, 3-phase, Y-connected alternator has an effective resistance of 0.40 ohm and a reactance of 6 ohms per phase. It delivers full load current of 0.80 lagging power factor at rated voltage. What will be the terminal voltage for the same excitation and load current if the power factor is 0.80 leading?

A.  4560 V

B.  9878 V

C.  7898 V

D.  4250 V

6.  REE Board Exam March 1998

A generator is rated 100 MW, 13.8 kV and 90% power factor. The effective resistance is 1.5 times the ohmic resistance. The ohmic resistance is obtained by connecting two terminals to a DC source. The current and voltage are 87.6 A and 6 V respectively. What is the effective resistance per phase? The generator is wye-connected.

A.  0.0513 ohm

B.  0.0685 ohm

C.  0.342 ohm

D.  0.0617 ohm

7.  REE Board Exam October 1997

To get the armature resistance of a 100 MW, 13.89 kV and 90% power factor generator, two terminals are connected to a DC source. The measured current and voltage are 87.6 amperes and 6 volts respectively. What is the DC resistance per phase?

A.  0.0223 ohm

B.  0.0342 ohm

C.  0.0685 ohm

D.  0.0617 ohm

8.  EE Board Exam October 1991

Determine the efficiency of a 1500 kVA, 2300 V, 3-phase, Y-connected alternator, which operates at rated output with a power factor of 80%. The DC armature resistance at 70°C between terminals is 0.08 ohm. The field takes 70 A at 120 V from the exciter equipment. Friction and windage losses are 15 kW, iron loss is 35 kW and stray load losses are 1.5 kW. Assume the effective armature winding resistance is 1.5 times the DC value.

A.  94.56%

B.  90.31%

C.  93.35%

D.  92.62%

9.  EE Board Exam April 1994

A three-phase, 11-kV wye-connected synchronous alternator has a synchronous reactance of 8 ohms per phase but negligible resistance. If the excitation is such that the open circuit voltage is 14 kV, determine the power factor at the maximum output.

A.  0.786

B.  0.772

C.  0.793

D.  0.708

10.  EE Board Exam April 1994

A three-phase AC generator is supplying power to a load of 3200 kW at 230 volts and a power factor of 60%. Assume that the loss of the line, the generator armature and the load is equal to the 10% of the load, what would be the savings in watts if the power factor were raised to 80%?

A.  100,000

B.  140,000

C.  80,000

D.  230,000

11.  EE Board Exam April 1992

A three-phase turbo alternator has a reactance of 15 ohms and negligible resistance, the machine draws an armature current of 250 amperes at 0.8 pf lagging when running on 12,000 volts infinite bus-bars. If the steam admission is constant but the emf is raised by 20%, calculate the new operating pf.

A.  0.547

B.  0.586

C.  0.509

D.  0.575

12.  EE Board Exam April 1980

A standby Diesel generator set will have the following loads: inductive load drawing 50 kVA at 0.8 power factor; Lighting load drawing 20 kVA at 1.0 power factor. At what power factor will the generator operate?

A.  0.855 lagging

B.  0.872 lagging

C.  0.821 lagging

D.  0.894 lagging

13.  EE Board Exam April 1992

A 250 V, 30 Hz generator supplies power to a parallel circuit consisting of a 20 hp motor whose efficiency is 90% at 0.80 pf lagging and a second load that draws an apparent power of 7 kVA at unity pf. Determine the system reactive power.

A.  23.582 kVAR

B.  12.435 kVAR

C.  10.341 kVAR

D.  20.384 kVAR

14.  EE Board Exam October 1980

Two alternators A and B are operating in parallel supplying a load drawing 1000 kVA at 0.80 power factor lagging. If alternator A contributes 500 kVA at 0.60 power factor lagging, determine the power factor of alternator B.

A.  0.928 lagging

B.  0.852 lagging

C.  0.901 lagging

D.  0.977 lagging

15.  EE Board Exam October 1981

Two alternators are operating in parallel supplying a common load of 425 kW at 0.85 power factor lagging. Alternator A contributes 600 kVAR at 0.92 power factor lagging. Solve for the power factor of alternator B.

A.  0.813 lagging

B.  0.834 lagging

C.  0.804 lagging

D.  0.820 lagging

16.  EE Board Exam April 1988

Sipalay Mines, has two 3-phase, 60 H AC generators operating in parallel. The first unit has a capacity of 1000 kVA and the second unit has a capacity of 1500 kVA. The first is driven by a prime mover so adjusted that the frequency falls from 61 Hz at no-load to 59.6 Hz at full-load. The second has a different speed load characteristics, the frequency falls from 61.4 Hz at no-load to 59.2 Hz at full-load. When these alternators are jointly delivering 2000 kW, what is the load of each generator?

A.  884 kW, 1116 kW

B.  867 kW, 1133 kW

C.  915 kW, 1085 kW

D.  804 kW, 1196 kW

17.  REE Board Exam March 1998

Two alternators are driven by shunt motors. The shunt motors have speed-load droop characteristics of 3% and 4% respectively. The alternators are in parallel and each carrying 50 kW. There is no automatic speed-load control. An additional 50 kW is switched on. What are the resulting loads of the alternators assuming that the speed-load control of each is not adjusted?

A.  78.57 kW, 71.43 kW

B.  82.51 kW, 67.49 kW

C.  75 kW, 75 kW

D.  80.31 kW, 69.69 kW

18.  EE Board Exam April 1989

There are two alternators, 100 kW, 3-phase in parallel are driven by shunt motors whose speed-load droop characteristics are as follows: Alternator no. 1: no-load speed 600 rpm and the full-load speed 530 rpm; while alternator no. 2: no-load speed 590 rpm and the full-load 550 rpm. For what load will the alternators divide the load equally?

A.  62.45 kW

B.  68.78 kW

C.  67.54 kW

D.  64.67 kW

19.  EE Board Exam April 1989

There are two alternators, 100 kW, 3-phase in parallel are driven by shunt motors whose speed-load droop characteristics are as follows: Alternator no. 1: no-load speed 600 rpm and the full-load speed 530 rpm; while alternator no. 2: no-load speed 590 rpm and the full-load 550 rpm. What is the greatest load that can be delivered without overloading either alternator?

A.  171.43 kW

B.  168.78 kW

C.  177.54 kW

D.  164.67 kW

20.  ECE Board Exam April 1998

Find the frequency in kilocyles per second in the armature of a 10 pole, 1,200 rpm generator.

A.  1000.0

B.  100.0

C.  10.00

D.  0.100

21.  A certain 3-phase, star-connected, 1,000 kVA, 11,000 volt alternator has rated current of 52.5 amperes. The dc resistance of the winding per phase is 0.3 ohm. The test results are given below:

	Field current	Line voltage
OC Test	12.5 A	422 volts
SC Test	12.5 A	52.5 A

Determine the full-load voltage regulation at unity power factor

A.  0.44%

B.  0.54%

C.  0.64%

D.  0.74%

22.  A 10 MVA, 10 kV, 3-phase, 50 Hz, 1,500 rpm alternator is parallel with each other much greater capacity. The moment of inertia of the rotor is 2 x 10⁵ kg-m² and the synchronous reactance of the machine is 40%. Calculate the natural time of oscillation.

A.  8.3 ms

B.  9.3 ms

C.  10.3 ms

D.  11.3 ms

23.  A 6.6 kV, Y-connected, 3-phase alternator has a synchronous reactance of 6 ohms per phase and a negligible resistance. At a certain field current the armature is known to induce 5.8 kV per phase. At this excitation, calculate the maximum power that can be produced.

A.  12 MW

B.  10 MW

C.  11 MW

D.  9.8 MW

24.  A 6.6 kV, Y-connected, 3-phase alternator has a synchronous reactance of 6 ohms per phase and a negligible resistance. At a certain field current the armature is known to induce 5.8 kV per phase. At this excitation, calculate the maximum current.

A.  2.83 kA

B.  3.83 kA

C.  4.83 kA

D.  5.83 kA

25.  A 6.6 kV, Y-connected, 3-phase alternator has a synchronous reactance of 6 ohms per phase and a negligible resistance. At a certain field current the armature is known to induce 5.8 kV per phase. At this excitation, calculate the power factor at maximum power.

A.  0.853

B.  0.863

C.  0.873

D.  0.843

26.  The frequency of voltage generated by an alternator having 4-poles and rotating at 1800 r.p.m. is ______ Hertz.

A.  60

B.  7200

C.  120

D.  450

27.  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

28.  The main disadvantage of using short-pitch in alternators is that it

A.  reduces harmonics in the generated voltage

B.  reduces the total voltage around the armature coils

C.  produces asymmetry in the three phase windings

D.  increases Cu of end connections

29.  Three-phase alternators are invariably Y-connected because

A.  magnetic losses are minimized

B.  less turns of wire are required

C.  smaller conductors can be used

D.  higher terminal voltage is obtained

30.  The winding of a 4-pole alternator having 36 slots and a coil span of 1 to 8 is short-pitched by _____ degrees.

A.  140

B.  80

C.  20

D.  40

31.  If an alternator winding has a fractional pitch of 5/6, the coil span is ____ degrees.

A.  300

B.  150

C.  30

D.  60

32.  The harmonic which would be totally eliminated from the alternator e.m.f. using a fractional pitch of 4/5 is

A.  3rd

B.  7th

C.  5th

D.  9th

33.  For eliminating 7th harmonic from the e.m.f. wave of an alternator, the fractional-pitch must be ______.

A.  2/3

B.  5/6

C.  7/8

D.  6/7

34.  If, in an alternator, chording angle for fundamental flux wave is α, its value for 5th harmonic is

A.  5α

B.  α/5

C.  25α

D.  α/25

35.  Regarding distribution factor of an armature winding of an alternator which is statement is false?

A.  it decreases the distribution of coils (slot/pole) increases

B.  higher its value, higher the induced e.m.f per phase

C.  it is not affected by the type of winding either lap or wave

D.  its not affected the number of turns per coil

36.  When speed of alternator is changed from 3600 r.p.m. to 1800 r.p.m. the generated e.m.f./phase will become

A.  one-half

B.  twice

C.  four times

D.  one-fourth

37.  The magnitude of the three voltages drops in an alternator due to armature resistance, leakage reactance and armature reaction is solely determined by

A.  load current, I_a

B.  p.f. of the load

C.  whether it is a lagging or leading p.f. load

D.  field construction of the alternator

38.  Armature reaction in an alternator primarily affects

A.  rotor speed

B.  terminal voltage

C.  frequency of armature current

D.  generated voltage per phase

39.  Under no-load condition, power drawn by the prime mover of an alternator goes to

A.  produce induced e.m.f in armature winding

B.  meet no load loss

C.  produce power in the armature

D.  meet Cu losses both in armature and rotor windings

40.  As load p.f of an alternator becomes more leading, the value of generated voltage required to give rated terminal voltage

A.  increases

B.  remains unchanged

C.  decreases

D.  varies with rotor speed

41.  With a load p.f. of unity, the effect of armature reaction on the main-field flux of an alternator is

A.  distortional

B.  magnetizing

C.  demagnetizing

D.  nominal

42.  At lagging loads, armature reaction in an alternator is

A.  cross-magnetizing

B.  demagnetizing

C.  non-effective

D.  magnetizing

43.  At leading p.f., the armature flux in an alternator ______ the rotor flux.

A.  opposes

B.  aids

C.  distorts

D.  does not affect

44.  The voltage regulation of an alternator having 0.75 leading p.f. load, no-load induced e.m.f of 2400 V and rated terminal voltage of 3000 V is ______.

A.  20

B.  -20

C.  150

D.  -26.7

45.  If, in a 3-Ф alternator, a field current of 50 A produces a full-load armature current of 200 A on short-circuit and 1730 V on open circuit, then its synchronous impedance is ____ ohm.

A.  8.66

B.  4

C.  5

D.  34.6

46.  The power factor of an alternator is determined by its

A.  speed

B.  load

C.  excitation

D.  prime mover

47.  For proper parallel operation a.c. polyphase alternators must have the same

A.  speed

B.  voltage rating

C.  kVA rating

D.  excitation

48.  Of the following conditions, the one which does NOT have to be met by the alternators working in parallel is

A.  terminal voltage of each machine must be the same

B.  the machine must have the same phase rotation

C.  the machine must operate at the same frequency

D.  the machine must have equal rating

49.  After wiring up two 3-Ф alternators, you checked their frequency and voltage and found them to be equal. Before connecting them in parallel, you would

A.  check turbine phase

B.  check phase rotation

C.  lubricate everything

D.  check steam pressure

50.  Zero power factor method of an alternator is used to find its

A.  efficiency

B.  voltage regulation

C.  armature resistance

D.  synchronous impedance

⇒ MCQ in AC Generators Part 2 | REE Board Exam