MCQ for Electrical Eng

MCQ For Electrical Eng.-1 1. a. b. c. The HVDC converter Does not consume reactive power Consumes as much reactive power as real power Consumes 50% of the real power Ans. c 2. A back to back HVDC link can be advantageous compared to AC primarily because a. It is cheaper b. Of stability considerations c. Of controlled power flow Ans. c 2. a. b. c. A 12-pulse bridge is preferred in HVDC because It eliminates certain harmonics It results in better power factor Series connection of converters on D.C. side is better 2. a. b. c. Fault on a two terminal DC link is removed by Breakers on DC side Breakers on AC side Current control of converters Ans. a Ans. c TRANSMISSION LINE 1. 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 MW b. (110) 2/440 MW c. (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 ohms Ans: (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. b. c. Vs =Vr Vs is greater than Vr Vs is less than Vr Ans: (c) 4. Voltage regulation of a short transmission line is a. always positive b. always negative c. either positive, negative, or zero Ans: (c) i. ii. a. b. c. 5. The capacitance of an overhead line increases with increase in mutual geometric mean distance increase in height of conductors above ground Both are true Both are false Only (i) is correct Ans: (b) a. b. c. 6. Shunt compensation for long EHV lines is primarily resorted to improve voltage profile improve stability reduce fault currents Ans: (a) 7. Series compensation is primarily resorted to d. improve voltage profile e. improve stability f. 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 V where f and V are the system frequency and voltage respectively. Ans: (a) a. b. c. 9. Bundled conductors are used in EHV lines primarily for reducing cost of the line reducing corona loss and radio interference 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 kV b. 3 kV25/ c. 3 kV25 Ans: (b) a. b. c. 11. Two or three sheds or petticoats are provided in pin-type insulators in order to increase creepage resistance spark-over voltage(S.O.V) puncture voltage Ans: (a) a. b. c. 12. Pin -type insulators are use up to 11 kV 33kV 132kV Ans: (b) 13. Insulators used for transmission line at the dead -end tower are a. suspension type b. shackle type c. strain type Ans: (c) 14. Economic studies have shown that D.C. transmission is cheaper than a. c transmission for lengths a. a. below 300 km b. b. beyond 600 km c. c. beyond 1200 km Ans. b 15.Transmission voltages in the range 230 kV-765 kV are known as a. a. High voltage b. b. Extra High Voltage c. c. Ultra High Voltage Ans. b 16. Which one of the following statements is false? As the transmission voltage increases, a. a. Corona loss decreases b. b. Conductor copper loss decreases c. 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 to a. a. 0.5 I * 10-7 H/m b. 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 conductors b. b. Current density in ACSR conductors is uniform c. c. The GMD between two circular areas, each of different diameters, is equal to the distance between their centres. Ans. b a. b. c. 19. a. b. c. Expanded ACSR conductors are used To increase the tensile strength of the line To reduce corona loss 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/19 b. b. L/361 c. 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/m b. b. 10-9/36pF/m c. c. 2 p210-7 F/m Ans .a a. b. c. 22. a. b. c. In a double-circuit line with hexagonal spacing , The phases are balanced, but the conductors of each individual phase are not balanced. The conductors of each individual phase are balanced , but the phases are not balanced 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 increased b. Resistance and internal inductance of a conductor both increase with increase of frequency c. Resistance of a conductor increases and the internal inductance decreases as the frequency is increased Ans. c 25. a. b. c. d. The surge impedance of a double-circuit power transmission line is 40 ohms 200 ohms 400 ohms 800 ohms Ans. b 26. The surge impedance of a telephone line is a. 50 ohms b. 75 ohms c. 200 ohms d. 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 bundle b. 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 D2. D1 is in parallel with another having parameters A2. 30. b. b.a. c. Lagging Unity Leading Ans. Skin effect increases the resistance of a conductor . 31. b MCQ For Electrical Eng. a. C1. A transmission line having parameters A1. b 19. B1. c. A1A2 +B1C2 (A1B2 +A2B1)/(B1+B2) C1+C2 + (A1-A2)(D2-D1)/(B1+B2) Ans. Which one of the following statements is true? a. b. b. a. c. b.but proximity effect decreases the resistance b. Ans. c. The percentage regulation of an overhead transmission line can be zero when the load power factor is a. c. d 29. a. b. a. a. B2. Increasing the spacing of power line conductors Transposing power line conductors Transposing communication line conductors Either b or c. c 18. c. 29. d. The overall " A " parameter of the combination is a. C2.-2 18. Both skin effect and proximity effect increase the resistance of a conductor c. d. a. b. Both skin effect and proximity effect increase the internal inductance of a conductor Ans. c. Disruptive critical voltage is Equal to . a. c. Decreases c. Greater than c. 32. b. 33. c 19. a. Increases b. b. Corona loss a. Handling of the telephone receiver may become dangerous due to Electromagnetic induction . Less than visual critical voltage for corona on an overhead line. Ans. Does not change the switching voltage on a transmission line. a. Ans. b 20. c.b. a. a. b 21. Dielectric strength of mechanically sound porcelain is 10 kV/cm 22 kV/cm 65 kV/cm . Mutual inductance between a three -phase power line and a telephone line due to third harmonic current in the power line is a. c. Zero Ans. b. b. 35. Ans.b. The algebraic sum of mutual inductances from individual phase wires b. c. b. a. b. Electrostatic induction Both electromagnetic and electrostatic induction from a power line. c. b 22. c. The arithmetic sum of mutual inductances from individual phase wires c. 34. c. 22 kV/cm 240 kV/cm Ans. 37. b. c 24. a. Which one of the following statements is true? For 11 kV insulators. c. 36. 60-66 kV/cm c.d. d. 140 kV/cm d.3 . b. the ratio of dry spark-over voltage to working voltage is 8. b. Dielectric strength of glass is a. d.3 For 66 kV insulators. a. the ratio of wet spark-over voltage to working voltage is 8. a. b. 100 kV/cm Ans. c 23. The spark-over voltage is equal to the puncture voltage . The spark-over voltage is less than the puncture voltage b. For 11 kV insulators. Which one of the following statements is true? a. c 25. The spark-over voltage is greater than the puncture voltage c.3 Ans. c. none of the above 26. Which one of the following statements is true? a. the ratio of dry spark-over voltage to working voltage is 8. c. c. a. a. c.c. 38. Routine tests are performed on 1/2 percent of insulators supplied Design tests are done on 1/2 percent of insulators supplied Ans. Flash-over tests are performed on all insulators b. b. b. 39. c. To conform to the equipotential surfaces and the body should be shaped to conform to the electrostatic tubes of force c. b. In a suspension insulator.Ans. To conform to the equipotential surfaces and so also the body Ans. a. a. c. b. c. a 27. 40. b 28. 41. the mechanical stresses on the conductor are Increased Reduced The same . Which one of the following statements is true? The sheds of an insulator should be shaped a. b. To conform to the electrostatic tube of force and the body should be shaped to conform to the equipotential surfaces b. a. a. a. b 29. The same as that for dry flash-over Ans. d. capacitance to earth/capacitance per insulator By the correct grading of various capacitances Decreasing the number of strings Ans.Ans. 43. String efficiency of insulators for wet flash-over is a. b. Less b. More c. c. The string efficiency of the insulator can be increased by Increasing the number of strings in the insulator Increasing the ratio . b . b. c 30. 42. b. c. d. c. a. The potential across insulator discs can be equalized by having The same capacitance for each unit The highest capacitance for the lowest unit and decreasing progressively the capacitance of other units c. c. a. a. The lowest capacitance for the lowest unit and increasing progressively the capacitance of other units Ans. b. b. 45. a. b.31. 44. c. Ans. b 32. a. c. b. c Grading ring serves the purpose of Equalizing the voltage distribution across discs An arcing shield Both equalizing the voltage distribution and acting as an arcing shield . 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.TRANSFORMERS - 1. 3/N2N1/ c. 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. 2. N1/N2 b. 3N1/N2/ Ans: (b) 2. a . 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.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. b 4. 3. 4. b . Ans. b 2. b 3. c voltage Ans. c machine is . c series motor at no load is a) a) Zero b) b) Infinity c) c) 1500 r. The speed of a d.C MOTOR Objective questions 1. m Ans. The function of the commutator in a d. A sinusoidal voltage of frequency 1 Hz is applied to the field of a d. p. The armature voltage will be a) a) 1 Hz square wave b) b) 1 Hz sin e wave c) c) d. c generator.D. 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.a) a) to change ac to dc b) b) to change alternating voltage to direct voltage c) c) for easy control of voltage Ans. Ans. . b 5. 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. 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 . If a dc motor is connected across an ac supply . and the motor will destroy itself. a 7. c . c 6. 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.Ans. 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. b 9. 10. d) The dummy coil in the dc machine is used to eliminate armature reaction . Ans. 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 10.8. 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.e) e) bring about mechanical balance of armature f) f) eliminate reactance voltage Ans. Interpoles in the armature of a dc generator are used to . . c 12. b 11. 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. the speed of the set is (a) (a) half of the speed of he motors when connected in parallel .5 times the applied voltage. Ans.a) a) b) b) neutralize the reactance voltage 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. In series –parallel control method when two dc series motors are connected in series . b 13. 13. c 14. 14. Dynamic braking. . Ans. armature current onl b. The reversal of speed of motors used as electric braking is known as a. c 16. 15. armature current and flux both Ans. Regenerative b. The armature torque of the dc shunt motor is proportional to a. Plugging c. b 15. 16. field flux c.(b) (b) ¼ th of the speed of the motors when connected in parallel (c) (c) same as in parallel. the frequency of electro-mechanical modes of oscillation lies in the range (a) 0. 17..-3 1. (pu). plugging regenerative braking dynamic braking Ans.The power angle characteristic of a machine-infinite bus system is P= 2 sin The initial operating angle is 60 deg. b 17. sqrt(31.5-2.7) rad/sec c. System frequency is 50 Hz. sqrt(62. The angular frequency of oscillation following small perturbation will be a. .: (a) 2. ii. The method used for braking in rolling mills is a.4) rad/sec b. b. a MCQ For Electrical Eng. sqrt(15. inertia constant H= 5 sec. 2. i. In an interconnected power system .5 Hz . c.8) rad/sec Ans.Ans. iii. a.(b) 1-10 Hz (c) 30-60 Hz Ans. 4. d. If the sending end and receiving end voltages for a 3-phase transmission line are each 33kV(line). a 5. d. the maximum power transmitted per phase will be a. 60 MW 30 MW 29 MW 28 MW Ans. b. c. a.: (a) Small and large perturbations 3. Greater than 90 deg. Equal to 90 deg. When the alternator stalls (near the stability limit) the armature current is . 3. c. c. The torque angle corresponding to the steady-state stability limit of a salient-pole alternator is a. and if the reactance of the line is 13 ohms per phase. b. b. b. 5. Ans. c. Less than 90 deg. d 4. Less than the rated value b. c.a. a INDUCTION MOTOR 1. Equal to the rated value. 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. (A) . b. Greater than the rated value c. Ans. the speed of the rotating magnetic field will be: (A) 940 RPM (B) 1000RPM (C) 1050 RPM (D) 1100 RPM Ans.2. A 3-phasde 50 Hz induction motor runs at speed of 940 RPM. (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) . (B) 2. The no-load speed of an induction motor is of the order of (A) 8% (B) 4% (C) 2% (D) 6% Ans. The power factor of a 3-phase induction motor at no load is approximately (A) 0.4. The rotor input is (A) 5 kW (B) 10 kW (C) 20 kW (D) 50 kW Ans. (B) 5.2 (B) 0. (C) 6.7 (C) 0. Full-load copper losses in a 3-phase 50 Hz 4-pole induction motor running at 1455 rpm are 300 W.85 (D) 1 Ans: (A) 8.The maximum torque in a 3-phase induction motor occurs at a slip . 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) . 10.(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. The starting torque in a single-phase induction motor is (A) High (B) Low (C) Zero (D) Very low Ans. (B) 9. A change of 55 in the supply voltage of an induction motor will produce a change of approximately a) a) 5% . The starting torque of a 3-phase induction motor can be increased by increasing a b c the rotor reactance the rotor resistance the stator resistance Ans. B 11. C 12.11. 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. 12. 14. 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. 13. a) a) Which one of the following motors is most suitable for signalling devices and timers? dc series motor . Ans. 17. D 15.b) b) 7% c) c) 10% d) d) 25% in the rotor torque. Ans. 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. D 13. 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. 15. b 2.b) b) ac series motor c) c) induction motor d) d) reluctance motor Ans. D Synchronous motors 1. Ans. 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. Which of the following statements is true? Short-pitched coils in the alternators are used to a) reduce the size of the machine . b 3. The armature reaction of an alternator will be completely magnetizing when load power factor is a) unity b) zero lagging c) zero leading d) 0. If two alternators are running in parallel and he voltage of one machine is suddenly increased the machine winding will burn both machines will stop c) synchronizing torque will be produced to restore synchronism .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. c 4. The armature flux of an alternator at unity power factor load will be a) demagnetizing b) of square waveform c) cross-magnetizing Ans.8 lagging Ans. Ans. c a) b) 5. the reactive component of the output is changed the active component of the output is changed the power factor of the load remains the same (a)and (b) occur simultaneously. If the input to the prime mover of an alternator ( in a system of three alternators) is kept constant. b. a. b. then a. c 6. b TRANSIENT STABILITY -OBJECTIVE TYPE QUESTIONS 1. 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. d. c. . and the excitation is changed.: © The critical clearing angle of a given power system for a certain fault is proportional to the Inertia Constant M proportional to the Inertia Constant M independent of M. Ans. Ans. a 7. c.Ans. : (b) 1. Equal area criterion of stability is applicable to a. installation of 3-pole auto-reclose circuit breakers c.: (c ) MCQ For Electrical Eng. About1 Ans. About 0.: (a) 1. In a two-machine power system. a multi-machine system.1. a power system should have a diversity factor a. c From the economic point of view . a Run-of-river plants are used for a. a The two-part tariff is based on . Base load operation b. a power system should have a load factor a. Which one of the following enhances the transient stability of a system the most a.5 c. installation of single pole auto-reclose circuit breakers Ans.12 b. Much higher c. Nearly equal to but less than one c. Almost equal Ans. About 0. proper choice of make and break capabilities of the circuit breakers b.-4 From the economic point of view . machine A delivers power to machine B. Peak load operation c. Greater than one Ans. negative Ans. Much less than 1 b. Much lower b. c Peak load hydro power plants compared to base load thermal plants have plant capacity factor a. a machine infinite bus system only b. Ans. A 3phase fault occurs at the terminals of machine A. both to a machine-infinite bus and a two-machine system c. Initial acceleration of machine A is (a) positive (b) zero a. Near base load Ans. b. the effect of increased penalty factor between a generating plant and system load centre is to decrease the load on the generating plant to increase the load on the plant to hold the plant load constant. Ans.: (a) 1.: (b) In economic operation of a power system .: (b) Incremental heat . b. Reactive power in a single-phase a. a. c. the cost of generation is maximum minimum not affected Ans. a. a. b. The circuit breaker rating relevant to transient stability is rated voltage rated operating time rated breaking current Ans: c ECONOMIC OPERATION -OBJECTIVE TYPE QUESTIONS When generating units in a power plant are loaded with equal incremental costs. MW and MVar MW and MVA MWH and MVA Ans. 1. Voltage times current times the sine of the angle between the voltage & current . Ans.a. Voltage times the current in a circuit b. c. b. 1. b. c CIRCUIT -BREAKERS . a. c. c. 1. all four above (b) i and iii (c) i and iv.rate curves for thermal generating units are used to determine the fuel cost in $/hour values to which the units should be loaded to decrease the fuel costs to a minimum none of the above. Which of the following results when a resistance is placed across the contacts of a circuit breaker i successful and effective interruption of current ii undue power loss in the resistor iii effective fault power dissipation iv control of rate of rise of restriking voltage. Ans: (c) 1.c circuit is a product of a. a.OBJECTIVE TYPE QUESTIONS 1. Voltage times the current times the cosine of the angle between the voltage & current c. c. Shunt inductive reactors Ans.c 1. The stator current will be very high b. the stator current will be very small d. b. c.a 5. the back emf will be more than the supply voltage Ans.b SHORT-CIRCUIT ANALYSIS -OBJECTIVE TYPE QUESTIONS . Series capacitors c. d.Ans. Series inductive reactors b.8 lagging p. May exceed the sending end voltage c. Is always less than the sending end voltage b. c. The minimum armature current of he synchronous condenser corresponds to 0. Increasing the speed of the machine Ans.c 5. Var compensation can be provided by installing a. Increasing the field current b.d 5. leading Vars are provided by a. Is always equal to the sending end voltage Ans. the receiving end voltage a. If a synchronous motor(properly synchronized to the supply) is running on no load with negligible loss then a.8 pf leading unity pf Ans. a.b 3.f zero pf lagging 0. b. On a long high voltage transmission line under heavy load conditions. the stator current will be zero c.b 4. Vars are characterized by the fact that they always flow From points of low voltage to points of high voltage From points of high voltage to points of low voltage Between two points having the same voltage Ans. When synchronous condensers are used to provide vars. a. In a lightly loaded transmission line of such a length that the capacitive reactance is appreciable. Decreasing the field current c. 1.5. transient reactance c. and zero sequence networks at the fault point are connected in parallel Ans: (b) 3. negative and zero sequence impedances of a transmission line are 0.short -circuit currents are greatly out of phase with load currents . looking from star side is infinite and looking from delta side is zero Ans: (a) 2.0. The positive. looking from star side is zero and looking from delta side is infinite b. system has symmetrical fault and the network is otherwise unbalanced c. The load currents in short-circuit calculations are neglected because i.7 pu.1 pu respectively. the negative sequence current flowing through the transformer will have a phase shift of a. Zm =0.6 pu Ans: (a) 3. The zero sequence impedances of an ideal star-delta connected transformer (stargrounded) a. (a) the positive and negative sequence networks at the fault point are connected in series (b) the positive and negative sequence networks at the fault point are connected in parallel (c) the positive. 30 deg.6 pu (c)Zs = 1 pu.5 and 1. Zm =0. Symmetrical component method of analysis is more useful when a.5 pu. b.2 pu (b) Zs = 0. -30deg c. The machine reactances used for computation of short circuit current ratings of a circuit breaker are a. Ans: (a) 2. negative. 120 deg. sub-transient reactance Ans: (c) 2. synchronous reactance b. looking from star side is zero and looking from delta side is also zero c.short-circuit currents are much lager than load currents ii. system has unsymmetrical fault and the network is unbalanced. The self (Zs) and mutual (Zm) impedances of the line will be given by (a) Zs = 0. system has unsymmetrical fault and the network is otherwise balanced b. If a positive sequence current passes through a transformer and its phase shift is 30 degrees. Zm =0. Ans: (b) 2. For a line to line fault analysis using symmetrical components. link operating b. Advantage of power system interconnection is a. (i) is wrong and (ii) is correct c.OBJECTIVE TYPE QUESTIONS 1. Fewer machines are required as reserve for operation at peak loads Ans. 0. 2 c. Ans: (c) 2. The positive sequence network of a sample power system is shown in Fig. d.21 Fig. Corona loss and radio and TV interference with D. the rating of one machine in the system b. 1 b. a 2. c system are less than in an a. c link of small capacity c.C. The interenal voltages of a 3-phase synchronous generator correspond to a.The correct alternative is a.1 c.C. Large systems may be interconnected with d.2 Ans: (c) 2. Negative sequence c. Large size circuit breakers are required because of large short-circuit currents b. Fault levels in an all a. 0. both (i) and (ii) are wrong b. The base value of a power system is chosen based upon a. Limitation on the critical length of underground cables for use in A. Machines of one system remain in step with machines of another system c. 3 Ans: (b) 2.C transmission by cables is used. The synchronous reactance of a modern large size turbogenerator in pu is nearest to a. 1.0 b. Which one of the following statements is not true? a. C no longer exists if D. c system with a D. The element Zcc of the bus impedance matrix Zbus will be a. transmission is less Ans. c 2. Zero sequence PER UNIT SYSTEM. Positive sequence b.2 and the primitive reactance of each element is marked in ohms. both (i) and (ii) are correct. the largest machine in the system . X(ohms)=X(%)*100*kV2 /kVA b. None of the above TOP old c. (A) Universal (C) DC shunt (B) synchronous (D) two-phase . A bank of three single-phase transformers is star-star connected and has a % reactance of 10%. 36. A transmission line has a pu reactance of 30 %. The speed-torque characteristics of a DC series motor are approximately similar to those of the _________motor. The percentage reactance can be converted into ohmic value with the following formula a. some average (rounded) values such that the pu machine ratings are not too large or too small. Ans: (c) 3. the pu reactance of the line will now be a.3% c. The same bank is then converted to satisfy rated star-delta connections. 24. 3 %10 c.8% Ans: (c) 4. If the working voltage is now increased to 110% of its original voltage ( the MVA rating of the line remaining the same). 33% b. 3 %10/ b. The per cent reactance of the transformer will now be a. 10 % Ans: (c) 4. X(ohms)=X(%)*kV2 /(1000*kVA) Ans. X(ohms)=X(%)*1000*kV2 /kVA c.c. (A) Series combination of RTh.c. In order to reduce the harmful effects of harmonics on the a. Indirect induction over (C) Coreless induction furnace (B) core type induction furnace (D) high frequency eddy current g. (A) inverse.C.c. (B) stepper motor (D) DC series motor (B) 1750 rpm (D) 1710 rpm Thevenin’s equivalent circuit consists of _________. .c. cannot 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. (B) Series combination of RTh. ETh and RL. i. tachometer is just a ________with one phase excited from the carrier frequency. (A) Synchronous condensers (C) Shunt filters (B) shunt capacitors (D) static compensators h. If the number of poles is now reduced to 4 with the frequency remaining constant. ETh. operated universal motor (D) hybrid stepper motor. The torque.04 is________Hz (A) 8 (C) 6 (B) 4 (D) 2 e. cannot f. transmission system ______are provided. The synchronous speed for a 3 phase 6-pole induction motor is 1200 rpm. The rotor frequency for a 3 phase 1000 RPM 6 pole induction motor with a slip of 0. operated universal motor has a ______characteristic and it______ be started under no-load condition. side of a high voltage D. (A) 1690 rpm (C) 1500 rpm a. (A) Two-phase a. servomotor (B) two-phase induction motor (C) a.d. can (C) inverse.c. can (D) nearly inverse. The torque-speed characteristics of an a. (A) (B) nearly inverse.c. the rotor speed with a slip of 5% will be _________. in a _____________is proportional to the square of the armature current (A) DC shunt motor (C) 2-phase servomotor j. An a. (C) Lagging. In a 3-phase synchronous motor (A) the speed of stator MMF is always more than that of rotor MMF. (D) 8. (B) does not change. 3-phase induction motor has a full load speed of 1440 r. (C) the speed of stator MMF is synchronous speed while that of rotor MMF is zero.m. the capacitor is connected (A) in series with main winding. (B) 6. (C) a 3-phase winding on stator and a single-phase winding on rotor. (B) Same. MCQ For Electrical Eng. (B) in series with auxiliary winding. ETh. b. The size of the feeder is determined primarily by . (D) a single-phase winding on stator and a commutator winding on rotor. (C) decreases. (C) 12. g. (A) In an R – L –C circuit. Leading. the volume of conductor (A) increases. As the voltage of transmission increases.(C) Parallel combination of RTh. A synchro has (A) a 3-phase winding on rotor and a single-phase winding on stator. h. d. f. (C) in series with both the windings. In a capacitor start single-phase induction motor. (D) rotor and stator MMF are stationary with respect to each other. (B) the speed of stator MMF is always less than that of rotor MMF. (D) Depends upon the value of Land C. (D) Parallel combination of RTh. the phase of the current with respect to the circuit voltage will be_________. (D) in parallel with auxiliary winding.-5 c. The number of poles of the motor are (A) 4. ETh and RL. (D) increases proportionately. A 50 Hz. (B) a 3-phase winding on stator and a commutator winding on rotor. e.p. m. (C) more than 4. An alternator is delivering rated current at rated voltage and 0. The resulting approximate variation in speed (A) (A) Both (C) and are doubled. relative to the rotor structure is (A) (A) 1500 r. a. c. (B) capacitor start and capacitor run motor.5% or more than 4. the required excitation will be (A) less. (C) (C) more or less.p. The speed of the rotor m. the voltage across the feeder.m. (A) split-phase motor.p.m. (C) 25 r. the percent variation of voltage in the feeder. (D) 75 r.1 the current it is required to carry. 4 pole. When the motor is delivering rated output.m. If it is required to deliver rated current at rated voltage and 0. is halved.5%.05.80 power-factor lagging load the voltage regulation will be (A) 4. (2x8) b. A balanced three-phase.(A) (B) (C) (D) Q. A ceiling fan uses (A) (B) (C) (D) f. (B) 1425 r. is doubled while (B) is halved. the distance of transmission. At full-load and 0.5% at full-load and unity power-factor. (B) more. (D) capacitor start motor.5%.f. d. In a dc shunt motor the terminal voltage is halved while the torque is kept constant. Choose the correct or best alternative in the following: a.m.8 powerfactor lagging case. A two-winding single phase transformer has a voltage regulation of 4. (D) and armature current is constant and is constant but will be is doubled. (C) universal motor.5%.8 power-factor leading. b.5%. the slip is found to be 0. e. (B) less than 4. A stepper motor is . 50 Hz voltage is applied to a 3 phase.p. (D) the same.p. induction motor. (D) 4. Speed of a motor is given by ___________. (B) back lash. (C) prevent the moisture from entering the cable. .(A) (A) a dc motor. Choose the correct or best alternative in the following: c. e. (D) (C) 60f/p. The sheath is used in cable to (A) provide strength to the cable. (D) 60 p/f. g. (D) a two phase motor. (C) slip. (B) a single-phase ac motor. c.1 The drive motor used in a mixer-grinder is a (A) dc motor. (A) regulation. b. (A) (C) d. (E) (F) (G) (2x8) (A) (B) (C) average demand / maximum demand. Q. A series RLC circuit will have unity power factor if operated at a frequency of __________. . (D) lag. (D) universal motor. a. (C) input/output. (D) avoid chances of rust on strands. (A) output/(output + losses). (B) provide proper insulation. (B) 120 p/f. (D) . (C) a multi-phase motor. . (A) 120 f/p. The difference between synchronous speed and the actual speed of an induction motor is known as ___________. h. The efficiency of a transformer is given as __________. Load factor is defined as _________. (B) (output + losses)/output. average demand / installed capacity. maximum demand / average demand. (B) induction motor. d. (C) synchronous motor. (B) . (D) (output + losses)/input. . (B) . (C) increase the current available. Slip rings for an induction motors are made of (A) Aluminium. (B) unity. (D) hysteresis motor Choose the correct or best alternative in the following: a. The “Superposition theorem” is essentially based on the concept of (A) duality. (C) lagging. (C) shaded pole motor.1 (A) capacitor motor. d. Like a resonant R-L-C circuit. (2x8) (B) linearity. (D) reduce the time required to fully charge them after use. f. The motor which has the least noise is the ________. (B) universal motor. b. (B) (A) has a power factor of unity. Cells are connected in parallel in order to (A) increase the voltage available. c.(H) (D) maximum demand / installed capacity. g. Which of the following motors has a high starting torque? ac series motor. (C) draws maximum current. Which of the following generating stations has the minimum running cost? (A) f. (B) offers minimum impedance. a parallel resonance circuit also _________. The power factor of a purely resistive circuit is (A) zero. (C) thermal power station. (D) . (D) diesel power plant. (D) Cobalt steel. e. (C) . (D) leading. (B) dc series motor. (C) reciprocity. h. (D) non-linearity. (A) hydro-electric station. (B) nuclear power station. The power taken by a 3-phase load is given by the expression (A) . (B) reduce cost of wiring. (C) Phosphor bronze. (B) Carbon. (D) magnifies current. Q. (D) synchronous motor. A step-up transformer increases (A) voltage. (D) air-gap flux.06 MHz (D) None of the aove g. Electrostatic type instruments are primarily used as : (A) Ammeter (C) Voltmeter (B) Watt meter (D) Ohmmeter d. Frequency can be measured by using: (A) Maxwell’s bridge (C) Hay’s bridge (B) Schering’s bridge (D) Wien’s bridge e. The bandwidth is : 225 MHz (C) 10 KHz (B) 1. g. (B) speed. (C) power. h. (A) Primary electrons (B) Secondary emission electrons (C) Both primary and secondary (D) None of the above emission electrons The Q factor of a coil at the resonant frequency of an RLC series circuit is 150. . An aquadag is used in a CRO to collect: (A) f. a. (C) magnetising current. (B) current. The effect of increasing the length of the air gap in an induction motor will be to increase (A) power factor. A set of readings has wide range and therefore it has: (A) Low precision (C) Low accuracy b. (D) frequency. (B) High precision (D) High accuracy Thermocouple instruments can be used for a frequency range: (A) up to 100 Hz (C) up to 1 Hz (B) up to 5000 Hz (D) 50 MHz and above c. Piezo electric transducers are: (A) Passive transducers (B) Active transducers.(C) induction motor. An 8 bit converter is used for a d. i. h.(C) Inverse transducers. If a transducer has an output impedance of (A) a constant current source (C) a constant impedance. When two batteries are connected in parallel.-6 (B) 78 mV (D) None of the above 1. 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.2 mV MCQ For Electrical Eng. 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. range of 0-10 V.m. 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.c. it behaves as : . (D) (B) and (C). it should be ensured that (a) they have same e. Find the weight of LSB (A) 39 mV (C) 39.f (b) they have same make (c) they have same ampere-hour capacity (d) they have identical internal resistance . and a load resistance of (B) a constant voltage source (D) none of the above For a radio receiver. 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. Equipment earthing is provided for (a) Safety of human being (b) Safety of equipments (c) Safety of starters and cables (d) None . 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. Which of the following information available on name plate of a motor? (a) HP rating (b) RPM (c) Frame model (d) All the above 7.4. Two types of earthings are provided: (a) Equipment earthing and (b) Neutral point earthing. p. (d) none of the above. (d) None. . (b) motor will draw high current. 11. (d) the hysteresis loss increases. of the motor. (c) for better cooling of the transformer. 12. (b) the eddy current loss increases. (c) there will be vibrations on driver and driven unit. (c) the hysteresis loss decreases. If the thickness of laminations is increased. If alignment is not proper.8. (a) double (b) one and half (c) three (d) six 10. then (a) the eddy current loss decreases. Conservator is used (a) to take up the expansion of oil due to temperature rise. The synchronous speed of a motor with 6 poles and operating at 50 Hz frequency is ___. (a) fuses will blow. (b) to act as oil storage. 9. The three phase squirrel cage induction motor takes approximately its full load current _______ times the h. m.p. 50 Hz. . (d) none of the above. 14. 8-pole squirrel cage induction motor will run at a speed (a) < 750 r. (c) both (a) and (b).p. The numbers of slip rings of a single-phase and three-phase converters are respectively (a) 1 and 3.m.p.m. motor starters are used (a) to increase the starting torque. (d) > 1500 r. If three 10µF capacitors are connected in parallel. 15.p. but < 1500 r. but < 1000 r.C. (c) > 1000 r. (b) > 750 r.m.m. A 3-phase. D.m.p.(a) 1500 (b) 1000 (c) 3000 (d) 750 13. (b) to limit the starting current. the net capacitance is (a) 10/3µF (b) 30µF (c) 3/10µF (d) 60µF 16.p. (d) None 19. (d) 1 and 6. (c) Protecting from short-circuit.v. 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 . winding and the bushing. 20. Use of ELCB is advisable for (a) human safety. (c) 1 Farad. Buchholz relay is placed (a) in between the conservation and the breather. (d) 10 Farad. (d) in between the l. (c) in between the h. same reactance as an inductor of 1 H at 50 Hz? (a) 10 micro-Farad. 18. What value of capacitance will give approx. winding and the bushing. (b) Ease to reset when trips. (b) 1 micro-Farad. (c) 2 and 6.v. 17.(b) 2 and 3. (b) in between the tank and the conservator. turn (c) Tesla (d) Coulomb 23. 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. 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 .C 22.B. Unit of magnetic flux is (a) Weber (b) Ampere . If the neutral wire breaks. the lamp likely to fuse first will be (a) 200W (b) 100W (c) 40 W (d) All lamps 24. Lamps of 40 W.21. 100 W and 200 W are connected in different phases of a 3 — phase 4 — wire supply. (b) the stator winding is connected to supply and the rotor winding is short-circuited. normally (a) the rotor winding is connected to supply and the stator winding is short-circuited.25.. (a) shunt (b) cumulative compound (c) differential compound (d) series 28.. (d) the stator winding is connected to supply and the rotor winding is open-circuited.. ………. 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.. The colour of good Transformer oil is (a) Pale Yellow (b) Black (c) White (d) None .. For induction motors. (c) both the stator and the rotor windings are connected to supply.motor will run at the highest speed.. When load is removed. 27. 29. 34. 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 voltmeter will read (a) Zero . 31. Wi = 15 KW and Wcu = 25 KW at full load. when R1 = R2 = R3 = R4 = R5 are low value resistors and the resistor R3 becomes open circuited. In a transformer. As shown in the figure. 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. 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. (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.