mcq for electrical eng

MCQ For Electrical Eng.-1

1. The HVDC convertera. Does not consume reactive powerb. Consumes as much reactive power as real powerc. Consumes 50% of the real powerAns. c2. A back to back HVDC link can be advantageous compared to AC primarily becausea. It is cheaperb. Of stability considerationsc. Of controlled power flowAns. c2. A 12-pulse bridge is preferred in HVDC becausea. It eliminates certain harmonicsb. It results in better power factorc. Series connection of converters on D.C. side is betterAns. a2. Fault on a two terminal DC link is removed bya. Breakers on DC sideb. Breakers on AC sidec. Current control of convertersAns. c

TRANSMISSION LINE1. The surge impedance of a 110 kV, 3-phase transmission line is 440 ohms. The surge impedance loading of the line is

a. 3 (110) 2/440 MWb. (110) 2/440 MWc. (110) 2 3110)/ 2 MW

Ans.: (b)

2.The capacitance and inductance per unit length of a 3-phase line, operating at 110 kV are .01 microfarad and 2.5 mH. The surge impedance of the line is(a) 50 ohms(b) 500 ohms(c) 250 ohmsAns: (b)

3. A long transmission line is energized at then sending end and is kept open circuited at the receiving end. The magnitudes of the sending end voltage Vs and of the receiving end voltage Vr satisfy the following relationship

a. Vs =Vr

b. Vs is greater than Vrc. Vs is less than Vr

Ans: (c)

4. Voltage regulation of a short transmission line isa. always positiveb. always negativec. either positive, negative, or zero

Ans: (c)

5. The capacitance of an overhead line increases withi. increase in mutual geometric mean distanceii. increase in height of conductors above grounda. Both are trueb. Both are falsec. Only (i) is correct

Ans: (b)

6. Shunt compensation for long EHV lines is primarily resorted toa. improve voltage profileb. improve stabilityc. reduce fault currents

Ans: (a)

7. Series compensation is primarily resorted tod. improve voltage profilee. improve stabilityf. reduce fault currents

Ans: (b)

8. Fair weather corona loss may be computed using the empirical formula given by Peterson. According to Peterson's formula corona loss is proportional to(a) f and V2(b) f 2 and V

a. f and Vwhere f and V are the system frequency and voltage respectively.Ans: (a)

9. Bundled conductors are used in EHV lines primarily fora. reducing cost of the lineb. reducing corona loss and radio interferencec. increasing stability limit.

Ans: (b)

10. There are 20 discs in the string of insulators of a 3-phase 400 kV transmission line. String efficiency is 80 %. The maximum voltage across any disc is

a. 25 kVb. 3 kV25/c. 3 kV25

Ans: (b)

11. Two or three sheds or petticoats are provided in pin-type insulators in order to increasea. creepage resistanceb. spark-over voltage(S.O.V)c. puncture voltage

Ans: (a)

12. Pin -type insulators are use up toa. 11 kVb. 33kVc. 132kV

Ans: (b)

13. Insulators used for transmission line at the dead -end tower area. suspension typeb. shackle typec. strain type

Ans: (c)

14. Economic studies have shown that D.C. transmission is cheaper than a. c transmission for lengthsa. a. below 300 kmb. b. beyond 600 kmc. c. beyond 1200 kmAns. b

15.Transmission voltages in the range 230 kV-765 kV are known asa. a. High voltageb. b. Extra High Voltagec. c. Ultra High Voltage

Ans. b

16. Which one of the following statements is false?As the transmission voltage increases,

a. a. Corona loss decreasesb. b. Conductor copper loss decreasesc. c. Cost of insulators, transformers, switches & circuit breakers increases

Ans. c

17. The internal inductance of a solid conductor of radius r and carrying a current I is equal toa. a. 0.5 I * 10-7 H/mb. b. 0.5 I * 10-7 exp(-1/4)*r H/m

c. c. 0.5 * 10-7 H/m

Ans. c

18. Which one of the following statements is not true?a. a. The GMD method of finding inductance does not apply to ACSR conductorsb. b. Current density in ACSR conductors is uniformc. c. The GMD between two circular areas, each of different diameters, is equal to the

distance between their centres.Ans. b

19. Expanded ACSR conductors are useda. a. To increase the tensile strength of the lineb. b. To reduce corona lossc. c. To reduce I2R loss

Ans. b

20. A conductor with 19 strands, each of same diameter and each having an inductance of L Henries is used for a transmission line. The total inductance of the conductor will be

a. a. L/19b. b. L/361c. c. 19L

Ans. a

21. The line to neutral capacitance of single -phase line with conductors of radius 1cm and spaced 1m apart is equal to

a. a. 10-9/72 F/mb. b. 10-9/36pF/mc. c. 2 p210-7 F/m

Ans .a

22. In a double-circuit line with hexagonal spacing ,a. a. The phases are balanced, but the conductors of each individual phase are not balanced.b. b. The conductors of each individual phase are balanced , but the phases are not balancedc. c. The phases, and the conductors of each individual phase are both balanced

Ans. c

23. Which one of the following statements is true?

a. Skin effect at 50 Hz is negligible for larger diameter conductors but becomes appreciable for smaller conductor.

b. Skin effect at 50 Hz is negligible whatever the diameter of the conductor.

c. Skin effect at 50 Hz is negligible for the smaller diameter conductors but becomes appreciable for the larger conductor conductor.

Ans. c

24. Which one of the following statements is true?

a. Resistance of a conductor decreases and the internal inductance increases as the frequency is increasedb. Resistance and internal inductance of a conductor both increase with increase of frequencyc. Resistance of a conductor increases and the internal inductance decreases as the frequency is increased

Ans. c

25. The surge impedance of a double-circuit power transmission line is

a. 40 ohmsb. 200 ohmsc. 400 ohmsd. 800 ohms

Ans. b

26. The surge impedance of a telephone line isa. 50 ohmsb. 75 ohmsc. 200 ohmsd. 400 ohms

Ans. b

27. Bundle conductors are preferred in EHV transmission lines because

a. It is easy to fabricate thin conductors and combine them to make a bundleb. Inductance of the line is reduced, and the corona loss, and radio & TV interference is minimized.c. Tower height is reduced and hence transmission cost is low.

Ans. b

28. Inductive interference between power & communication lines can be minimized by

a. a. Increasing the spacing of power line conductorsb. b. Transposing power line conductors

c. c. Transposing communication line conductorsd. d. Either b or c.

Ans. d

29. The percentage regulation of an overhead transmission line can be zero when the load power factor is

a. a. Laggingb. b. Unityc. c. Leading

Ans. c

18. 29. Which one of the following statements is true?

a. a. Skin effect increases the resistance of a conductor ,but proximity effect decreases the resistance

b. b. Both skin effect and proximity effect increase the resistance of a conductorc. c. Both skin effect and proximity effect increase the internal inductance of a conductor

Ans. b

19. 30. A transmission line having parameters A1, B1, C1, D1 is in parallel with another having parameters A2, B2, C2, D2. The overall " A " parameter of the combination is

a. a. A1A2 +B1C2b. b. (A1B2 +A2B1)/(B1+B2)c. c. C1+C2 + (A1-A2)(D2-D1)/(B1+B2)

Ans. b


18. 31. Disruptive critical voltage is

a. a. Equal to

b. b. Greater than

c. c. Less than

visual critical voltage for corona on an overhead line.

Ans. c

19. 32. Corona loss

a. a. Increases

b. b. Decreases

c. c. Does not change

the switching voltage on a transmission line.

Ans. b

20. 33. Handling of the telephone receiver may become dangerous due to

a. a. Electromagnetic induction

b. b. Electrostatic induction

c. c. Both electromagnetic and electrostatic induction

from a power line.

Ans. b

21. 34. Mutual inductance between a three -phase power line and a telephone line due to third

harmonic current in the power line is

a. a. The algebraic sum of mutual inductances from individual phase wires

b. b. The arithmetic sum of mutual inductances from individual phase wires

c. c. Zero

Ans. b

22. 35. Dielectric strength of mechanically sound porcelain is

a. a. 10 kV/cm

b. b. 22 kV/cm

c. c. 65 kV/cm

d. d. 100 kV/cm

Ans. c

23. 36. Dielectric strength of glass is

a. a. 22 kV/cm

b. b. 60-66 kV/cm

c. c. 140 kV/cm

d. d. 240 kV/cm

Ans. c


a. a. For 11 kV insulators, the ratio of wet spark-over voltage to working voltage is 8.3

b. b. For 66 kV insulators, the ratio of dry spark-over voltage to working voltage is 8.3

c. c. For 11 kV insulators, the ratio of dry spark-over voltage to working voltage is 8.3

Ans. c


a. a. Flash-over tests are performed on all insulators

b. b. Routine tests are performed on 1/2 percent of insulators supplied

c. c. Design tests are done on 1/2 percent of insulators supplied

Ans. none of the above


a. a. The spark-over voltage is less than the puncture voltage

b. b. The spark-over voltage is greater than the puncture voltage

c. c. The spark-over voltage is equal to the puncture voltage

Ans. a


The sheds of an insulator should be shaped

a. a. To conform to the electrostatic tube of force and the body should be shaped to conform

to the equipotential surfaces

b. b. To conform to the equipotential surfaces and the body should be shaped to conform to

the electrostatic tubes of force

c. c. To conform to the equipotential surfaces and so also the body

Ans. b

28. 41. In a suspension insulator, the mechanical stresses on the conductor are

a. a. Increased

b. b. Reduced

c. c. The same

Ans. b

29. 42. The string efficiency of the insulator can be increased by

a. a. Increasing the number of strings in the insulator

b. b. Increasing the ratio , capacitance to earth/capacitance per insulator

c. c. By the correct grading of various capacitances

d. d. Decreasing the number of strings

Ans. c

30. 43. String efficiency of insulators for wet flash-over is

a. a. Less

b. b. More

c. c. The same

as that for dry flash-over

Ans. b

31. 44. The potential across insulator discs can be equalized by having

a. a. The same capacitance for each unit

b. b. The highest capacitance for the lowest unit and decreasing progressively the capacitance

of other units

c. c. The lowest capacitance for the lowest unit and increasing progressively the capacitance

of other units

Ans. b

32. 45. Grading ring serves the purpose of

a. a. Equalizing the voltage distribution across discs

b. b. An arcing shield

c. c. Both equalizing the voltage distribution and acting as an arcing shield

Ans. c

TRANSFORMERS -

1. For a delta-star 3-phase transformer the primary winding has N1 turns/phase and a secondary

has N2 turns /phase. The single-phase equivalent circuit will have a turns ratio

a. N1/N2

b. 3/N2N1/

c. 3N1/N2/

Ans: (b)

2. 2. The use of higher flux density in transformer design

a) a) reduces the transformer weight per kVA

b) b) increases the weight/kVA

c) c) increases the weight/kW

Ans. a

3. 3. The conservator is used in a transformer because

a) a) it supplies oil to the transformer whenever needed

b) b) protects the transformer from damage when oil expands due to rise in temperature

c) c) it provides fresh air and cools down the oil.

Ans. b

4. 4. Which of the following has the highest efficiency?

a) a) dc shunt motor

b) b) transformer

c) c) induction motor

d) d) synchronous motor

Ans. b

D.C MOTOR Objective questions

1. The speed of a d. c series motor at no load is

a) a) Zero

b) b) Infinity

c) c) 1500 r. p. m

Ans. b

2. A sinusoidal voltage of frequency 1 Hz is applied to the field of a d. c generator. The

armature voltage will be

a) a) 1 Hz square wave

b) b) 1 Hz sin e wave

c) c) d. c voltage

Ans. b

3. The function of the commutator in a d. c machine is

a) a) to change ac to dc

b) b) to change alternating voltage to direct voltage

c) c) for easy control of voltage

Ans. b

4. The direction of rotation of a dc series motor can be reversed

a) a) by interchanging the supply terminals

b) b) by interchanging the field terminals

c) c) either a) or b).

Ans. b

5. A dc shunt generator driven at normal speed in the normal direction fails to build up

armature voltage because

a) a) the armature resistance is high

b) b) the field current is not sufficiently high

c) c) there is no residual magnetism.

Ans. c

6. If a dc motor is connected across an ac supply , the dc motor will

a) a) burn as the eddy currents in the field produce heat

b) b) run at its normal speed

c) c) run at a lower speed

Ans. a

7. What would happen if the field of dc shunt motors is opened?

a) a) the speed of the motor will be reduced

b) b) it will run at its normal speed

c) c) the speed will be enormously high , and the motor will destroy itself.

Ans. c

8. Which one of the following motors is used in a locomotive?

a) a) Induction motor

b) b) dc series motor

c) c) Synchronous motor

Ans. b

9. The efficiency of a dc shunt generator has a maximum value when

a) a) magnetic losses are equal to mechanical losses

b) b) armature copper loss is equal to the constant loss

c) c) field copper loss is equal to the constant loss.

Ans. b

10. 10. The dummy coil in the dc machine is used to

d) eliminate armature reaction

e) e) bring about mechanical balance of armature

f) f) eliminate reactance voltage

Ans. b

11. The sparking at the brushes in a dc generator is attributed to

a) quick reversal of current in the coil under commutation

b) armature reaction

c) reactance voltage

Ans. . c

12. Interpoles in the armature of a dc generator are used to

a) a) neutralize the reactance voltage

b) b) neutralize the reactance voltage and the cross-magnetizing effect of the armature

reaction

c) c) neutralize the cross-magnetizing effect of the armature reaction

Ans. b

13. 13. The mechanical power develop by the dc motor is maximum when

a) a) back emf = applied voltage

b) b) back emf = 0

c) c) back emf = 0.5 times the applied voltage.

Ans. c

14. 14. In series –parallel control method when two dc series motors are connected in series , the

speed of the set is

(a) (a) half of the speed of he motors when connected in parallel

(b) (b) ¼ th of the speed of the motors when connected in parallel

(c) (c) same as in parallel.

Ans. b

15. 15. The armature torque of the dc shunt motor is proportional to

a. armature current onl

b. field flux

c. armature current and flux both

Ans. c

16. 16. The reversal of speed of motors used as electric braking is known as

a. Regenerative

b. Plugging

c. Dynamic braking.

Ans. . b

17. 17. The method used for braking in rolling mills is

a. i. plugging

b. ii. regenerative braking

c. iii. dynamic braking

Ans. a


1. (pu).The power angle characteristic of a machine-infinite bus system is P= 2 sin The initial operating angle is 60 deg., inertia constant H= 5 sec. System frequency is 50 Hz. The angular frequency of oscillation following small perturbation will be

a. sqrt(31.4) rad/sec

b. sqrt(15.7) rad/sec

c. sqrt(62.8) rad/sec

Ans.: (a)

2. 2. In an interconnected power system ,the frequency of electro-mechanical modes of oscillation lies in the range

(a) 0.5-2.5 Hz

(b) 1-10 Hz

(c) 30-60 Hz

Ans.: (a) Small and large perturbations

3. 3. If the sending end and receiving end voltages for a 3-phase transmission line are each 33kV(line), and if the reactance of the line is 13 ohms per phase, the maximum power transmitted per phase will be

a. a. 60 MW

b. b. 30 MW

c. c. 29 MW

d. d. 28 MW

Ans. d

4. 4. The torque angle corresponding to the steady-state stability limit of a salient-pole alternator is

a. a. Less than 90 deg.

b. b. Greater than 90 deg.

c. c. Equal to 90 deg.

Ans. a

5. 5. When the alternator stalls (near the stability limit) the armature current is

a. a. Less than the rated value

b. b. Greater than the rated value

c. c. Equal to the rated value.

Ans. a

INDUCTION MOTOR

1. The speed at which the rotating magnetic field produced by stator currents rotates in an induction motor is:

(A) Synchronous speed(B) Rotor speed

(C) Greater than synchronous speed

Ans. (A)

2. A 3-phasde 50 Hz induction motor runs at speed of 940 RPM; the speed of the rotating magnetic field will be:

(A) 940 RPM

(B) 1000RPM

(C) 1050 RPM

(D) 1100 RPM

Ans. (B)

2. The no-load speed of an induction motor is of the order of

(A) 8%

(B) 4%

(C) 2%

(D) 6%

Ans. (C)

3. Iron losses in the rotor of a 3-phase induction motor are negligible, because

(A) Frequency of rotor emf is too low

(B) Flux linking the rotor is of constant magnitude

(C) Flux density in the rotor parts is too low

Ans: (A)

4. Full-load copper losses in a 3-phase 50 Hz 4-pole induction motor running at 1455 rpm are 300 W. The rotor input is

(A) 5 kW (B) 10 kW

(C) 20 kW

(D) 50 kW

Ans. (B)

5. The no-load current of a 3-phase induction motor in terms of its full-load current is of the order of(A) 5%(B) 10%

(C) 25%

(D) 50%

Ans. (C)

6. The power factor of a 3-phase induction motor at no load is approximately

(A) 0.2

(B) 0.7

(C) 0.85

(D) 1

Ans: (A)

8.The maximum torque in a 3-phase induction motor occurs at a slip

(A) R2/ X2

(B) X2/ R2

(C) R22/ X2

(D) R22/ X22

Ans: (A)

9. For high starting torque, the most 3-phase induction motor is

(A) Squirrel-cage type

(B) Slip-ring type

(C) Deep bar squirrel-cage type

(D) Double-cage induction motor

Ans. (B)

9. 10. The starting torque in a single-phase induction motor is

(A) High

(B) Low

(C) Zero

(D) Very low

Ans. (C)

11. The efficiency of a single-phase induction motor as compared to a 3-phase induction motor rating is

(A) Lower

(B) Higher

(C) Equal

Ans: (A)

10. 12. The starting torque of a 3-phase induction motor can be increased by increasing

a the rotor reactance

b the rotor resistancec the stator resistance

Ans. B

11. 13. The maximum starting torque in the induction motor is developed when the rotor reactance is

a) a) half of the rotor resistance

b) b) twice of the rotor resistance

c) c) equal to the rotor resistance

Ans. C

12. 14. A change of 55 in the supply voltage of an induction motor will produce a change of approximately

a) a) 5%

b) b) 7%

c) c) 10%

d) d) 25%

in the rotor torque.

Ans. D

13. 15. The transformation ratio of an induction motor can be found by

a) a) blocked rotor test

b) b) open circuit test

c) c) slip test

d) d) stator resistance test

14. 16. The crawling in the induction motor is caused by

a) a) improper design of the machine

b) b) low supply voltage

c) c) high loads

d) d) harmonics developed in the motor.

Ans. D

15. 17. Which one of the following motors is most suitable for signalling devices and timers?

a) a) dc series motor

b) b) ac series motor

c) c) induction motor

d) d) reluctance motor

Ans. D

Synchronous motors

1. The damper winding in the synchronous moor is often used to

a) Prevent hunting only

b) Prevent hunting & provide the starting toque

c) Maintain synchronism

d) provide the starting torque only.

Ans. b

2. Which of the following statements is true?Short-pitched coils in the alternators are used to

a) reduce the size of the machine

b) reduce the harmonics or to eliminate the harmonics from the generated emf

c) provide accurate phase difference of 120 degrees between phases

d) reduce copper losses.

Ans. b

3. The armature flux of an alternator at unity power factor load will be

a) demagnetizing

b) of square waveform

c) cross-magnetizing

Ans. c

4. The armature reaction of an alternator will be completely magnetizing whenload power factor isa) unity

b) zero lagging

c) zero leading

d) 0.8 lagging

Ans. c

5. If two alternators are running in parallel and he voltage of one machine is suddenly increaseda) the machine winding will burnb) both machines will stop

c) synchronizing torque will be produced to restore synchronism

Ans. c

6. If the input to the prime mover of an alternator ( in a system of three alternators) is kept constant, and the excitation is changed, then

a. the reactive component of the output is changedb. the active component of the output is changedc. the power factor of the load remains the samed. (a)and (b) occur simultaneously. Ans. a

7. The coupling angle or load angle of a synchronous motor is defined as the angle between the

a) a) rotor and the stator poles of same polarity

b) b) rotor and the stator poles of opposite polarity

c) c) rotor and stator teeth

Ans. b

TRANSIENT STABILITY -OBJECTIVE TYPE QUESTIONS

1. The critical clearing angle of a given power system for a certain fault isa. proportional to the Inertia Constant Mb. proportional to the Inertia Constant Mc. independent of M.Ans.: © 1. Equal area criterion of stability is applicable toa. a machine infinite bus system onlyb. both to a machine-infinite bus and a two-machine system

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c. a multi-machine system.Ans.: (b)1. In a two-machine power system, machine A delivers power to machine B. A 3-phase fault occurs at the terminals of machine A. Initial acceleration of machine A is(a) positive(b) zeroa. negativeAns.: (a)1. Which one of the following enhances the transient stability of a system the mosta. proper choice of make and break capabilities of the circuit breakersb. installation of 3-pole auto-reclose circuit breakersc. installation of single pole auto-reclose circuit breakersAns.: (c )


From the economic point of view , a power system should have a load factora. About 0.12b. About 0.5c. About1Ans. cFrom the economic point of view , a power system should have a diversity factora. Much less than 1b. Nearly equal to but less than onec. Greater than oneAns. cPeak load hydro power plants compared to base load thermal plants have plant capacity factora. Much lowerb. Much higherc. Almost equalAns. aRun-of-river plants are used fora. Base load operationb. Peak load operationc. Near base loadAns. aThe two-part tariff is based on a. MW and MVarb. MW and MVAc. MWH and MVA

Ans. c CIRCUIT -BREAKERS - OBJECTIVE TYPE QUESTIONS

1. Which of the following results when a resistance is placed across the contacts of a circuit breakeri successful and effective interruption of currentii undue power loss in the resistoriii effective fault power dissipationiv control of rate of rise of restriking voltage.

a. all four above(b) i and iii(c) i and iv.Ans: (c)

1. The circuit breaker rating relevant to transient stability isa. rated voltageb. rated operating timec. rated breaking current

Ans: cECONOMIC OPERATION -OBJECTIVE TYPE QUESTIONS

1. When generating units in a power plant are loaded with equal incremental costs, the cost of generation is

a. maximumb. minimumc. not affected

Ans.: (b)1. Incremental heat - rate curves for thermal generating units are used to determine thea. fuel cost in $/hourb. values to which the units should be loaded to decrease the fuel costs to a minimumc. none of the above.

Ans.: (b)1. In economic operation of a power system , the effect of increased penalty factor between a

generating plant and system load centre isa. to decrease the load on the generating plantb. to increase the load on the plantc. to hold the plant load constant.

Ans.: (a)1. Reactive power in a single-phase a.c circuit is a product ofa. Voltage times the current in a circuitb. Voltage times the current times the cosine of the angle between the voltage & currentc. Voltage times current times the sine of the angle between the voltage & currentAns.c1. In a lightly loaded transmission line of such a length that the capacitive reactance is appreciable, the receiving end voltagea. Is always less than the sending end voltage

b. May exceed the sending end voltagec. Is always equal to the sending end voltageAns.b3. On a long high voltage transmission line under heavy load conditions, Var compensation can be provided by installinga. Series inductive reactorsb. Series capacitorsc. Shunt inductive reactorsAns.b

4. If a synchronous motor(properly synchronized to the supply) is running on no load with negligible loss thena. The stator current will be very highb. the stator current will be zeroc. the stator current will be very smalld. the back emf will be more than the supply voltageAns.c5. The minimum armature current of he synchronous condenser corresponds toa. 0.8 lagging p.fb. zero pf laggingc. 0.8 pf leadingd. unity pfAns.d5. When synchronous condensers are used to provide vars, leading Vars are provided bya. Increasing the field currentb. Decreasing the field currentc. Increasing the speed of the machineAns.a5. Vars are characterized by the fact that they always flowa. From points of low voltage to points of high voltageb. From points of high voltage to points of low voltagec. Between two points having the same voltageAns.bSHORT-CIRCUIT ANALYSIS -OBJECTIVE TYPE QUESTIONS1. If a positive sequence current passes through a transformer and its phase shift is 30 degrees, the negative sequence current flowing through the transformer will have a phase shift ofa. 30 deg.b. -30degc. 120 deg.

Ans: (b)2. The zero sequence impedances of an ideal star-delta connected transformer (star-grounded)a. looking from star side is zero and looking from delta side is infiniteb. looking from star side is zero and looking from delta side is also zeroc. looking from star side is infinite and looking from delta side is zeroAns: (a)2. The positive, negative and zero sequence impedances of a transmission line are 0.5,0.5 and 1.1 pu respectively. The self (Zs) and mutual (Zm) impedances of the line will be given by(a) Zs = 0.7 pu, Zm =0.2 pu(b) Zs = 0.5 pu, Zm =0.6 pu(c)Zs = 1 pu, Zm =0.6 puAns: (a)3. Symmetrical component method of analysis is more useful whena. system has unsymmetrical fault and the network is otherwise balancedb. system has symmetrical fault and the network is otherwise unbalancedc. system has unsymmetrical fault and the network is unbalanced.Ans: (a)2. For a line to line fault analysis using symmetrical components,(a) the positive and negative sequence networks at the fault point areconnected in series(b) the positive and negative sequence networks at the fault point areconnected in parallel(c) the positive, negative, and zero sequence networks at the fault point areconnected in parallelAns: (b)3. The machine reactances used for computation of short circuit current ratings of a circuit breaker area. synchronous reactanceb. transient reactancec. sub-transient reactanceAns: (c)2. The load currents in short-circuit calculations are neglected because

i. short-circuit currents are much lager than load currentsii. short -circuit currents are greatly out of phase with load currents

The correct alternative is a. both (i) and (ii) are wrongb. (i) is wrong and (ii) is correctc. both (i) and (ii) are correct.Ans: (c)

2. The positive sequence network of a sample power system is shown in Fig.2 and the primitive reactance of each element is marked in ohms. The element Zcc of the bus impedance matrix Zbus will bea. 1.0b. 0.1c. 0.21Fig.2Ans: (c)2. Which one of the following statements is not true?a. Fault levels in an all a. c system are less than in an a. c system with a D.C. link operatingb. Large systems may be interconnected with d. c link of small capacityc. Limitation on the critical length of underground cables for use in A. C no longer exists if D.C transmission by cables is used.d. Corona loss and radio and TV interference with D.C. transmission is lessAns. a2. Advantage of power system interconnection isa. Large size circuit breakers are required because of large short-circuit currentsb. Machines of one system remain in step with machines of another systemc. Fewer machines are required as reserve for operation at peak loadsAns. c2. The interenal voltages of a 3-phase synchronous generator correspond toa. Positive sequenceb. Negative sequencec. Zero sequencePER UNIT SYSTEM- OBJECTIVE TYPE QUESTIONS1. The synchronous reactance of a modern large size turbogenerator in pu is nearest toa. 1b. 2c. 3Ans: (b)2. The base value of a power system is chosen based upona. the rating of one machine in the systemb. the largest machine in the systemc. some average (rounded) values such that the pu machine ratings are not too large or too small.Ans: (c)3. A bank of three single-phase transformers is star-star connected and has a % reactance of 10%. The same bank is then converted to satisfy rated star-delta connections. The per cent reactance of the transformer will now bea. 3 %10/ b. 3 %10

c. 10 %Ans: (c)4. A transmission line has a pu reactance of 30 %. If the working voltage is now increased to 110% of its original voltage ( the MVA rating of the line remaining the same), the pu reactance of the line will now bea. 33%b. 36.3%c. 24.8%Ans: (c)4. The percentage reactance can be converted into ohmic value with the following formulaa. X(ohms)=X(%)*100*kV2 /kVAb. X(ohms)=X(%)*1000*kV2 /kVAc. X(ohms)=X(%)*kV2 /(1000*kVA)Ans. None of the above TOP

old c. The speed-torque characteristics of a DC series motor are approximately similar to those of the

_________motor.

(A) Universal (B) synchronous(C) DC shunt (D) two-phase

d. The rotor frequency for a 3 phase 1000 RPM 6 pole induction motor with a slip of 0.04 is________Hz

(A) 8 (B) 4(C) 6 (D) 2

e. The torque-speed characteristics of an a.c. operated universal motor has a ______characteristic and it______ be started under no-load condition.

(A) inverse, can (B) nearly inverse, can(C) inverse, cannot (D) nearly inverse, cannot

f. In the heating process of the ________type a simple method of temperature control is possible by means of a special alloy which loses its magnetic properties at a particular high temperature and regains them when cooled to a temperature below this value.

(A) Indirect induction over (B) core type induction furnace(C) Coreless induction furnace (D) high frequency eddy current

g. In order to reduce the harmful effects of harmonics on the a.c. side of a high voltage D.C. transmission system ______are provided.

(A) Synchronous condensers (B) shunt capacitors(C) Shunt filters (D) static compensators

h. An a.c. tachometer is just a ________with one phase excited from the carrier frequency.

(A) Two-phase a.c. servomotor (B) two-phase induction motor(C) a.c. operated universal motor (D) hybrid stepper motor.

i. The torque, in a _____________is proportional to the square of the armature current

(A) DC shunt motor (B) stepper motor(C) 2-phase servomotor (D) DC series motor

j. The synchronous speed for a 3 phase 6-pole induction motor is 1200 rpm. If the number of poles is now reduced to 4 with the frequency remaining constant, the rotor speed with a slip of 5% will be _________.

(A) 1690 rpm (B) 1750 rpm(C) 1500 rpm (D) 1710 rpm

a. Thevenin’s equivalent circuit consists of _________.

(A) Series combination of RTh, ETh and RL. (B) Series combination of RTh, ETh.

(C) Parallel combination of RTh, ETh. (D) Parallel combination of RTh, ETh and RL.

b. In an R – L –C circuit, the phase of the current with respect to the circuit voltage will

be_________.

(A) Leading. (B) Same.(C) Lagging. (D) Depends upon the value of Land C.


c. A 50 Hz, 3-phase induction motor has a full load speed of 1440 r.p.m. The number of poles of the motor are

(A) 4. (B) 6.

(C) 12. (D) 8.

d. In a 3-phase synchronous motor

(A) the speed of stator MMF is always more than that of rotor MMF. (B) the speed of stator MMF is always less than that of rotor MMF.

(C) the speed of stator MMF is synchronous speed while that of rotor MMF is zero. (D) rotor and stator MMF are stationary with respect to each other.

e. In a capacitor start single-phase induction motor, the capacitor is connected

(A) in series with main winding. (B) in series with auxiliary winding.(C) in series with both the windings. (D) in parallel with auxiliary winding.

f. A synchro has

(A) a 3-phase winding on rotor and a single-phase winding on stator. (B) a 3-phase winding on stator and a commutator winding on rotor.(C) a 3-phase winding on stator and a single-phase winding on rotor. (D) a single-phase winding on stator and a commutator winding on rotor.

g. As the voltage of transmission increases, the volume of conductor

(A) increases. (B) does not change. (C) decreases. (D) increases proportionately. h. The size of the feeder is determined primarily by

(A) the current it is required to carry. (B) the percent variation of voltage in the feeder. (C) the voltage across the feeder. (D) the distance of transmission.

Q.1 Choose the correct or best alternative in the following: (2x8)

a. a. A two-winding single phase transformer has a voltage regulation of 4.5% at full-load

and unity power-factor. At full-load and 0.80 power-factor lagging load the voltage regulation will be

(A) 4.5%. (B) less than 4.5%. (C) more than 4.5%. (D) 4.5% or more than 4.5%.

b. b. In a dc shunt motor the terminal voltage is halved while the torque is kept constant. The

resulting approximate variation in speed and armature current will be

(A) (A) Both and are doubled. (B) is constant and is doubled.

(C) is doubled while is halved. (D) is constant but is halved.

c. A balanced three-phase, 50 Hz voltage is applied to a 3 phase, 4 pole, induction motor. When the motor is delivering rated output, the slip is found to be 0.05. The speed of the rotor m.m.f. relative to the rotor structure is

(A) (A) 1500 r.p.m. (B) 1425 r.p.m.

(C) 25 r.p.m. (D) 75 r.p.m.

d. An alternator is delivering rated current at rated voltage and 0.8 power-factor lagging case. If it is required to deliver rated current at rated voltage and 0.8 power-factor leading, the required excitation will be

(A) less. (B) more.(C) (C) more or less. (D) the same.

e. A ceiling fan uses

(A) (A) split-phase motor. (B) (B) capacitor start and capacitor run motor.(C) (C) universal motor. (D) (D) capacitor start motor.

f. A stepper motor is

(A) (A) a dc motor. (B) a single-phase ac motor.(C) a multi-phase motor. (D) a two phase motor.

g. The sheath is used in cable to

(A) provide strength to the cable. (B) provide proper insulation. (C) prevent the moisture from entering the cable. (D) avoid chances of rust on strands.

h. The drive motor used in a mixer-grinder is a

(A) dc motor. (B) induction motor. (C) synchronous motor. (D) universal motor. Q.1 Choose the correct or best alternative in the following: (2x8)

c. a. A series RLC circuit will have unity power factor if operated at a frequency of __________.

(A) . (B) .

(C) . (D) .

d. b. The difference between synchronous speed and the actual speed of an induction motor is known as ___________.

(A) regulation. (B) back lash.(C) slip. (D) lag.

c. The efficiency of a transformer is given as __________. (A) output/(output + losses). (B) (output + losses)/output.(C) input/output. (D) (output + losses)/input.

d. Speed of a motor is given by ___________.

(A) 120 f/p. (B) 120 p/f.(D) (C) 60f/p. (D) 60 p/f.

e. Load factor is defined as _________.

(E) (A) average demand / maximum demand.(F) (B) average demand / installed capacity.(G) (C) maximum demand / average demand.(H) (D) maximum demand / installed capacity.

f. Like a resonant R-L-C circuit, a parallel resonance circuit also _________.

(B) (A) has a power factor of unity. (B) offers minimum impedance.(C) draws maximum current. (D) magnifies current.

g. Slip rings for an induction motors are made of

(A) Aluminium. (B) Carbon.(C) Phosphor bronze. (D) Cobalt steel.

h. The motor which has the least noise is the ________.

(A) capacitor motor. (B) universal motor. (C) shaded pole motor. (D) hysteresis motorQ.1 Choose the correct or best alternative in the following: (2x8)

a. The “Superposition theorem” is essentially based on the concept of (A) duality. (B) linearity. (C) reciprocity. (D) non-linearity.

b. Cells are connected in parallel in order to

(A) increase the voltage available. (B) reduce cost of wiring.(C) increase the current available. (D) reduce the time required to fully charge them after use.

c. The power factor of a purely resistive circuit is

(A) zero. (B) unity.(C) lagging. (D) leading.

d. The power taken by a 3-phase load is given by the expression

(A) . (B) .

(C) . (D) .

e. Which of the following generating stations has the minimum running cost?

(A) hydro-electric station. (B) nuclear power station.(C) thermal power station. (D) diesel power plant.

f. Which of the following motors has a high starting torque?

(A) ac series motor. (B) dc series motor.(C) induction motor. (D) synchronous motor.

g. A step-up transformer increases

(A) voltage. (B) current.(C) power. (D) frequency.

h. The effect of increasing the length of the air gap in an induction motor will be to increase

(A) power factor. (B) speed. (C) magnetising current. (D) air-gap flux.

a. A set of readings has wide range and therefore it has:

(A) Low precision (B) High precision(C) Low accuracy (D) High accuracy

b. Thermocouple instruments can be used for a frequency range:

(A) up to 100 Hz (B) up to 5000 Hz(C) up to 1 Hz (D) 50 MHz and above

c. Electrostatic type instruments are primarily used as :

(A) Ammeter (B) Watt meter(C) Voltmeter (D) Ohmmeter

d. Frequency can be measured by using:

(A) Maxwell’s bridge (B) Schering’s bridge(C) Hay’s bridge (D) Wien’s bridge

e. An aquadag is used in a CRO to collect:

(A) Primary electrons (B) Secondary emission electrons(C) Both primary and secondary (D) None of the above

emission electrons f. The Q factor of a coil at the resonant frequency of an RLC series circuit is 150. The bandwidth

is :

(A) 225 MHz (B) 1.06 MHz(C) 10 KHz (D) None of the aove

g. Piezo electric transducers are:

(A) Passive transducers (B) Active transducers.(C) Inverse transducers. (D) (B) and (C).

h. If a transducer has an output impedance of and a load resistance of , it behaves as :

(A) a constant current source (B) a constant voltage source(C) a constant impedance. (D) none of the above

i. For a radio receiver, its sensitivity indicates:

(A) a response which is spurious (B) the ability to reject an unwanted signed

(C) the measure of noise produced (D) the receiver’s ability to pick up weak signal

j. An 8 bit converter is used for a d.c. range of 0-10 V. Find the weight of LSB

(A) 39 mV (B) 78 mV(C) 39.2 mV (D) None of the aboveMCQ For Electrical Eng.-6

1. The failure % of electric motor is higher due to (a) Bearing failure (b) Insulation failure (c) Over loading (d) None

2. In case of induction motor, Star I Delta starter is used (a) To prevent the motor from tripping (b) Because it connects motor automatically in Delta winding (c) To save the cost of H R C fuses (d) None

3. When two batteries are connected in parallel, it should be ensured that

(a) they have same e.m.f

(b) they have same make

(c) they have same ampere-hour capacity

(d) they have identical internal resistance

4. Which of the following is an AC motor?

(a) Slip ring motor

(b) Synchronous motor

(c) Squirrel cage Induction motor

(d) All of the above

5. In Transformer, oil is used for (a) Cooling the Transformer (b) Providing insulation to Transformer winding and for cooling the Transformer (c) Lubricating the Transformer (d) None

6. Which of the following information available on name plate of a motor?

(a) HP rating

(b) RPM

(c) Frame model

(d) All the above

7. Two types of earthings are provided: (a) Equipment earthing and (b) Neutral

point earthing. Equipment earthing is provided for

(a) Safety of human being (b) Safety of equipments (c) Safety of starters and cables (d) None

8. Conservator is used (a) to take up the expansion of oil due to temperature rise. (b) to act as oil storage.

(c) for better cooling of the transformer. (d) none of the above.

9. The three phase squirrel cage induction motor takes approximately its full load current _______ times the h.p. of the motor.

(a) double

(b) one and half

(c) three

(d) six

10. If the thickness of laminations is increased, then (a) the eddy current loss decreases. (b) the eddy current loss increases. (c) the hysteresis loss decreases. (d) the hysteresis loss increases.

11. If alignment is not proper, (a) fuses will blow. (b) motor will draw high current. (c) there will be vibrations on driver and driven unit. (d) None.

12. The synchronous speed of a motor with 6 poles and operating at 50 Hz frequency is ___.

(a) 1500

(b) 1000

(c) 3000

(d) 750

13. A 3-phase, 50 Hz, 8-pole squirrel cage induction motor will run at a speed (a) < 750 r.p.m. (b) > 750 r.p.m. but < 1000 r.p.m. (c) > 1000 r.p.m. but < 1500 r.p.m. (d) > 1500 r.p.m.

14. D.C. motor starters are used

(a) to increase the starting torque.

(b) to limit the starting current.

(c) both (a) and (b).

(d) none of the above.

15. If three 10µF capacitors are connected in parallel, the net capacitance is

(a) 10/3µF

(b) 30µF

(c) 3/10µF

(d) 60µF

16. The numbers of slip rings of a single-phase and three-phase converters are respectively

(a) 1 and 3.

(b) 2 and 3.

(c) 2 and 6.

(d) 1 and 6.

17. Buchholz relay is placed (a) in between the conservation and the breather. (b) in between the tank and the conservator.

(c) in between the h.v. winding and the bushing. (d) in between the l.v. winding and the bushing.

18. Use of ELCB is advisable for (a) human safety. (b) Ease to reset when trips. (c) Protecting from short-circuit. (d) None

19. What value of capacitance will give approx. same reactance as an inductor of 1 H at 50 Hz? (a) 10 micro-Farad. (b) 1 micro-Farad. (c) 1 Farad. (d) 10 Farad.

20. High battery voltage can be obtained by

(a) connecting cells in series

(b) connecting cells in parallel

(c) using large size cells

(d) increasing quantity of electrolyte

21. The transformer in which the winding is surrounded by the core is known as

(a) shell type

(b) core type

(c) tertiary type

(d) none of the above A,B,C

22. Unit of magnetic flux is

(a) Weber

(b) Ampere - turn

(c) Tesla

(d) Coulomb

23. Lamps of 40 W, 100 W and 200 W are connected in different phases of a 3 — phase 4 — wire supply. If the neutral wire breaks, the lamp likely to fuse first will be

(a) 200W (b) 100W (c) 40 W (d) All lamps

24. What of the following is commonly used for extending the range of an AC ammeter?

(a) a current transformer

(b) a capacitor

(c) a shunt

(d) an inductor

25. An ideal transformer has maximum efficiency when

(a) copper losses are equal to iron losses

(b) copper losses are less than iron losses

(c) copper losses are more than iron losses

(d) copper losses and iron losses are equal to windage losses

26. For induction motors, normally

(a) the rotor winding is connected to supply and the stator winding is short-circuited. (b) the stator winding is connected to supply and the rotor winding is short-circuited. (c) both the stator and the rotor windings are connected to supply.

(d) the stator winding is connected to supply and the rotor winding is open-circuited.

27. When load is removed, ……….......motor will run at the highest speed.

(a) shunt

(b) cumulative compound

(c) differential compound

(d) series

28. The colour of good Transformer oil is

(a) Pale Yellow

(b) Black

(c) White

(d) None

29. The capacity of a battery is expressed in terms of

(a) current rating

(b) voltage rating

(c) ampere-hour rating

(d) none of the above

30. The main purpose of performing open-circuit test on a transformer is to measure its

(a) Cu loss (b) core loss (c) total loss (d) insulation resistance.

31. In a transformer, Wi = 15 KW and Wcu = 25 KW at full load. Total loss at maximum efficiency will be (a) 30 KW (b) 40 KW (c) 50 KW (d) 20 KW

33. Which of the following is not a basic element of a transformer? (a) core (b) primary winding (c) secondary winding (d) mutual flux.

34. As shown in the figure, when R1 = R2 = R3 = R4 = R5 are low value resistors and the resistor R3 becomes open circuited, the voltmeter will read

(a) Zero (b) 50V (c) 125 V (d) 250 V

35. H.R.C fuse is

(a) a ceramic body having metal end caps

(b) a wire of platinum

(c) a heavy cross-section of copper or aluminium

(d) a ceramic tube having carbon rod inside it.

mcq for electrical eng

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