EE Refresher

Electrical Engineering Department Refresher Exam EE Subject Name:__________________________________ Direction: Solve the following problem and select the best answer. 1. It is desired to measure the insulation resistance between the motor winding and the motor frame, frame, a 300-volt 30,000 ohm voltmeter voltmeter in making the measurement. The voltmeter connected across the source reads 230 volts and when connected in series with the insulation reads 5 volts. Find the insulation resistance?  A. 1.5 mega-ohms. C. 1.25 mega-ohms. B. 1.35 mega-o hms . D. 2.0 mega-ohms. 2. A wire has a resistance of 1.0 ohm per 1000 ft at diameter of 0.1 inch. Determine the the resistance of a 200 ft long conductor conductor if the diameter is 40 mils.  A. 2.5 C. 1.25 B. 25 D. 12.5 3. Two coils in a network are positioned such such that there is 80% coupling between them. If the inductance inductance of one coil is 12 mH and the other is 6 mH, find the mutual inductance.  A. 6.8 mH C. 4.8 mH B. 8.6 mH D. 8.2 mH 4. A capacitor is charged at 100,000 micro-coulomb in 2 seconds. seconds. What is the current in mA?  A. 0.5 C. 5 B. 0.005 D. 50 5. A coil of 50 ohm resistance and of 150 mH inductance is connected is is parallel with a 50 micro-farad capacitor. The source voltage voltage is 100 sin (ώ ( ώt +30deg). What is the equation of the line current?  A. 1.91 sin (ώ (ώt + 52.5deg) B. 1.82 sin ( ώt – 62deg)  – 62deg) C. 1.25 sin (ώ ( ώt + 75.5deg) D. 1.32 sin (ώ (ώt –75.5deg)  –75.5deg) 6. Two current, 5+j2 and 3-j2 enter a junction. What is the out going current?  A. 2+j4A C. 2A B. 8A D. 8-j4A 7. A single phase induction induction motor motor is rated 5hp, 75% power factor and 220 volts. What approximate size of capacitor is necessary to raise the power factor to about 95%?  A. 3 kvar C. 2.5 kvar B. 2 kvar  D. 3.5 kvar 8. A load of 10,000 KVA, KVA, 85% power factor lagging lagging is connected to a 13,200 volt line. line. How much reactive power is needed to correct the power factor to 97% lagging?  A. 5,156 KVAR KVAR C. 3,138 KVAR B. 2,547 KVAR D. 4,753 KVAR 9. What capacitance must must be placed in series series with an inductance inductance of 0.05 H so that that at 100 Hz, the impedance impedance becomes equal to the the ohmic resistance?  A. 50 uF C. 35.5 uF B. 70.7 uF D. 87 uF 10. One leg of a radio tuned circuit has a capacitance capacitance of one times ten ten to the minus nine farad. It is turned at 200 KHz, KHz, what is the inductance of the other leg in henry?  A. 6.33 x 10 -7 C. 20 x 10-3 B. 8.25 x 10 -5 D. 120 x 10-3 11. A balanced balanced delta connected load of 4 – j3  – j3 ohms/phase is fed by a 380 V, 3-phase system. Find the reactive power. power.  A. 52 kVARS C. 69 kVARS B. 29 kVARS D. 87 kVARS 12. A balanced three phase wye connected source has using negative phase phase sequence, Vca = 398 Vrms with 90 degrees angle. Determine Van.  A. 230 + j 0 V C. 115 115 –  – j199  j199 V B. -115 – -115 – j199  j199 V D. – D. – j230  j230 V 13. A balanced 3-phase wye connected source has using ABC phase sequence, Van Van = 230 Vrms with 30 degrees angle. Determine Determine Vbc  A. 190.5 + j330 V C. -190.5 – -190.5 – j330  j330 V B. 190.5 – 190.5 – j330  j330 V D. – D. – j381  j381 V 14. A 240 V (line to neutral) three-phase three-phase source is connected to three 10 ohm resistance loads with both source and load in the Yconfiguration. Determine the current in each phase  A. 22 A C. 24 A B. 20 A D. 28 A 15. In a balanced three-phase system, the wye-connected impedances connected are 10 ohms with with 30 degrees angle. If Vbc is equal to 416 V with 240 degrees angle, determine Icn. Assume the phase sequence is a bc.  A. 12 + j20.8 A C. 12 – 12 – j20.8  j20.8 A B. 20.8 – 20.8 – j12 A D. 20.8 + j12 A 16. A 10 kva, 440/110 440/110 volts 60 Hz 2-winding transformer is used as an autotransformer What is the kva rating if it is used as 550/110 volts autotransformer?  A. 40 C. 12.5 B. 25 D. 50 17. A 100 kva, 2300/230 volts volts 60 Hz 2-winding transformer is used as an autotransformer having a single winding to to step up the voltage of a 2300 volts line by 10%. If the transformer has 3.3% impedance as 2-winding transformer, find the % impedance as autotransformer.

 A. 0.3 C. 33 B. 0.003 D. 0.033 18. A 500 hp, 2400V, 3-phase motor of 90 percent factor and 95 percent efficiency is to be operated from a 13.8 kV utility service through a wye-delta connected transformers. Compute the secondary winding current in ampere of the transformer.  A. 157.3 C. 104.9 B. 125.6 D. 60.6 19. What is the possible synchronous speed in rpm of a 10 pole induction motor used on 60 cycle line?  A. 1200 C. 720 B. 1800 D. 3600 20. A three phase generator with full load current of 450 at 12,400 volts has 0.08 ohm, resistance and a synchronous reactance of 2.8 ohms, what is the regulation in percent at 75 percent pow 21. er factor lagging?  A 12.8 C. 14.3 B. 18.9 D. 21.5 22. A 500 kva single phase transformer with 5% reactance is to share a load of 750 kva at 80% pf lagging with a 333 kva single phase transformer with 4% reactance. Calculate the kva delivered by each transformer.  A. 375 each C. 333 & 417 B. 350 & 400 D. 340 & 410 23. What is the slip in percent of a 6 pole synchronous motor running 1170 rpm?  A. 2.5% C. 2% B. 3 % D. 0 24. What is the slip in percent of an induction motor running 427 rpm?  A. 2.5% C. 2% B. 3 % D. 5% 25. An AC generator 1500 kva capacity has a full load efficiency of 91% at 100% power factor and 86% at 80% power factor lagging current. What engine drive in HP is required if the genset is to supply entirely motor loads?  A. 3125 C. 1870 B. 2525 D. 2210 26. Three 333 kva transformers are delta connected, one connection has been cut, what is the maximum kva that can be supplied by the remaining transformers?  A. 333 C. 677 B. 577 D. 423 27. A short circuit test was performed on a 15 kva, 2400/240 volts transformer yields the following results: Short circuit current = 6.25  Amp, short circuit voltage=131 volts and short circuit power=214 watts. Determine the %VR at full load 80% power factor lagging  A. 4.35% C. 4.5% B. 4.8% D. 5.2% 28. A 250 kVA 20000/240 volts single phase transformer operates at: Full-load ,0.8 p.f. lagging for 11 hours; Half load at unity pf for 8 hours; 25% load at 95% pf leading for the rest of the day The core loss is 1800 Watts and full load copper loss is 2500 Watts. What is the all –day efficiency?  A. 97.9% C. 96.2% B. 98.5% D. 98.7% 29. What should be the turn ratio of a three phase transformer to transform 10 MVA from 230 kv to 4160 volts if the transformer is connected wye-delta?  A. 31.92 C. 55.29 B. 95.76 D. 21.39 30. A single circuit, three phase 60 Hz transmission line consist of three conductors each of 250 mils in diameter arranged in triangular formation 5m, 5m and 8 m apart. Find the inductive reactance per km.  A. 0.5858 ohm C. 0.8686 ohm B. 0.6868 ohm D. 0.8585 ohm 31. What is the standard device number for overvoltage relay?  A. 46 C. 64 B. 27 D. 59 32. A single phase 10 km transmission line has 16.65 mH total inductance. If the distance between the conductor is 1.0 m, What is the GMR of conductor?  A. 1.662 cm C. 1.864 cm B. 1.558 cm D. 1.238 cm 33. Two generator 50 MVA, 4 kV X g1=25% are connected in parallel and are connected to a transformer 100 MVA 4.2 kV delta / 115kV wye grounded with Xt1=10%. What is the available short circuit MVA at the transformer secondary?  A. 286 C. 356 B. 578 D. 435 34. What is the standard device number for Directional Power Relay?  A. 37 C. 32 B. 40 D. 27 35. A short 3-phase transmission line has an impedance of 8+j11 ohm per phase. The sending end voltage is 120 kV when supplying a balanced load at 110 kV, 0.9 power fac tor lagging. What is the Receiving end power in MW.  A. 110MW C. 43.2MW B. 142MW D. 81.6MW 36. A three phase, 13 kv transmission line delivers 8 MVA of load. The per phase impedance of the line is (0.01+j0.05) pu referred to a 13 kv, 8 MVA base. What is the voltage drop across the line?  A. 886 volts C. 769 volts B. 663 volts D. 595 volts 37. The per phase constants of a 345 kv, three phase, 150 km long transmission line has a resistance of 0.1 ohm per km, inductance

of 1.1 mH per km and capacitance of 0.02 uF per km. The line supplies a 180MW load at 0.9 power factor lagging.. Using nominal pi, calculate the B constant?  A. 68.86 cis 75.86o C. 67.69 cis 86.44o B. 63.98 cis 76.44o D. 65.95 cis75.55o 38. A 33 kv 3-phase generating station is to supply 10 MW load at 31 kv, 0.9 power factor lagging over a 3-phase transmission line 3 km long. For the efficiency of the line to be 96%, what must be the impedance of the line?  A. 3.24+j7.8 C. 3.24+j6.4 B. 3.24+j5.9 D. 3.24+j8.7 39. The capacitance between any two conductor with the third connected to the sheath of a three phase, 3-conductor cable is 0.2 µF per km. What is total capacitance to neutral for 10km line?  A. 2µF C. 4µF B. 5µF D. 6µF. 39. At a certain location in an electric system, the available fault MVA is 400 MVA. A 15 MVA, 34.5 kV/6.24kV, 2.5% impedance, wyewye grounded transformer is installed at that location. Determine the short circuit MVA at the secondary .  A. 195 MVA C. 90 MVA B. 150 MVA D. 240 MVA 40. There was a phase to phase fault at 13.8 kV system where the Thevenin’s equivalent impedance is 2.63% what is the magnitude of the fault current. Base MVA is 10 .  A. 15,900 amperes C. 7970 amperes B. 13,800 amper es D. 27,600 amperes 41. A 5 MVA, 13.8 kV / 480 V, 5% impedance transformer is tapped at 13.8 kV line where the Thevenin’s equivalent impedance is ½ ohm. Determine the fault current at the primary for a three-phase fault at the secondary.  A. 10,500 amperes C. 42000 amperes B. 3300 amperes D. 6050 amperes 42. The units of capacitance are  A. volts/coulomb C. ohms B. coulombs/volts D. henry/Wb 43. “The total electric flux through any closed surface surrounding charges is equal to the amount of charge enclosed”. The abo ve statement is associated with  A. Coulomb’s square law C. Maxwell’s first law B. Gauss’s law D. Maxwell’s second law 44. For which of the following parameter variation, the capacitance of the capacitor remains unaffected?  A. Distance between plates C. Nature of dielectric B. Area of the plates D. Thickness o f the plates 45. Voltage across capacitor at any time T during charging from a DC source of voltage V is given by  A.

C.

B.

D.

46. The breakdown voltage for paper capacitors is usually  A. 20 to 60 volts C. 2000 to 3000 volts B. 200 to 1600 volts D.more than 10000 volts 47. The direction of magnetic lines of force is  A. from South Pole to north pole B. from one end of the magnet to another C. from North Pole to south po le D. none of the above 48. The two conductors of a transmission line carry equal current I in opposite direction. The force on each conductor is  A. proportional to I B. proportional to distance between conductors C. proportional to D. inversely proportional to 49. A material which is slightly repelled by a magnetic field is known as  A. ferromagnetic material C.paramagnetic material B. diamagnetic material D. conducting material 50. The ratio of intensity of magnetization to the magnetization force is known as  A. flux density C.susceptibility B. relative permittivity D. none of the above 51. Paramagnetic materials have relative permeability  A. slightly < 1 C. slightl y > 1 B. equal to unity D. ≤ 1 52. The unit of magnetic flux is  A. henry C. weber  C. ampere-turn/weber D. ampere/meter 53. Permeability in a magnetic circuit corresponds to ___ in an electric circuit.  A. resistance C. resistivity B. conductivity D. conductance 54. The initial rate of rise of current through a coil of inductance 10 H when suddenly connected to a DC supply of 200 V is ___ A/s  A. 50 C. 20 B. 0.05 D. 500 55. The property of a material which opposes the creation of magnetic flux in it is known as  A. reluctivity C. permeance B. magneto motive force D. reluctance

56. Laminated cores, in electrical machines, are used to reduce  A. copper loss C. eddy current loss B. hysteresis loss D. all of the above 57. The direction of induced emf can be found by  A. Laplace’s law C. Fleming’s right hand rule B. Lenz’s law D. Kirchhoff’s voltage law 58. The co-efficient of self inductance for a coil is given as  A.

C.

B.

D.

59. The self inductances of two coils are 8 mH and 18 mH. If the co-efficient of coupling is 0.5, the mutual inductance of the coil is  A. 4 mH C. 5 mH B. 6 mH D. 12 Mh 60. A 500 turns solenoid develops an average induced voltage of 60 V. Over what time interval must a flux change of 0.06 Wb occur to produce such a voltage?  A. 0.01 s C. 0.1 s B. 0.5 s D. 5 s 61. A conductor carries 125 amperes of current under 60° to a magnetic field of 1.1 tesla. The force on the conductor will be nearly  A. 68.75 N/m C. 120 N/m B. 240 N/m D. 480 N/m 62. “The mass of an ion liberated at an electrode is directly proportional to the quantity of electricity”. The above statement is associated with  A. Newton’s law B. Faraday’s law o f electromagnetic induction C. Faraday’s law of electrolysis D. Gauss’s law 63. The specific gravity of electrolyte is measured by  A. manometer C. a chemical gauge B. hydrometer  D. psychrometer 64. The capacity of a lead-acid cell is measured in  A. amperes C. ampere-hour s B. watts D. watt-hours 65. Five 2 V cells are connected in parallel. The output voltage is  A. 10 V C. 1.5 V B. 1.75V D. 2 V 66. The storage battery generally used in electric power station is  A. nickel-cadmium battery C. lead-acid b attery B. zinc-carbon battery D. none of the above 67. An AC current is given by I = 200 sin 100  A.

C.

B.

D.

. It will achieve a value of 100 A after ___ second.

68. The peak value of a sine wave is 200 V. Its average value is  A. 127. 4 V C. 141.4 V B. 282.8 V D. 200 V 69. The power consumed in a circuit element will be least when the phase difference between the current and voltage is  A. 180° C. 90° B. 60° D. 0° 70. The rms value and mean value is the same in the case of  A. triangular wave C. sine wave C. square wave D. half wave rectifier sine wave 71. For a frequency of 200 Hz, the time period will be  A. 0.05 s C. 0.005 s B. 0.0005 s D. 0.5 s 72. Lamination of core are generally made of  A. cast iron C. carbon B. silicon steel D. stainless steel 73. The commutator segments are connected to the armature conductors by means of  A. co pp er l ug s C. resistance wires B. insulation pads D. brazing 74. For a DC generator when the number of poles and the number of armature conductors is fixed, then which winding will give the higher emf?  A. lap winding C. Either of (a) and (b) above B. wave winding D. depends on the design 75. Iron losses in a DC machine are independent of variation in  A. speed C. load B. voltage D. speed and voltage 76. Brushes of DC machines are made of  A. car bo n C. soft copper B. hard copper D. all of above

77. No-load speed of which of the following motor will be highest?  A. shunt motor C. cumulative compound motor B. series motor  D. differential compound motor 78. If a DC motor is to be selected for conveyors, which motor would be preferred?  A. Seri es motor  C. differentially compound motor B. Shunt motor D. Cumulative compound motor 79. Small DC motors up to 5 H.P. usually have  A. 2 po les C. 4 poles B. 6 poles D. 8 poles 80. The mechanical power developed by a shunt motor will be maximum when the ratio of back emf to applied voltage is  A. 4.0 C. 2.0 B. 1.0 D. 0.5 81. The speed of a motor falls from 1100 rpm at no-load to 1050 rpm at rated load. The speed regulation of the motor is  A. 4.54% C. 4.76% B. 6.77% D. 8.84% 82. The no-load current drawn by transformer is usually what per cent of the full-load current?  A. 0.2 to 0.5 percent C. 12 to 15 percent B. 2 to 5 percent D. 20 to 30 percent 83. The dielectric strength of transformer oil is expected to be  A. 1 kV C. 33 kV B. 100 kV D. 330 Kv 84. Which of the following is not a part of transformer installation?  A. conservator C. breather B. Buchholz relay D. exciter 85. A common method of cooling a power transformer is  A. natural air cooling C. oil cooling B. air blast cooling D. any of the above 86. The maximum efficiency of a distribution transformer is  A. at no load C. at 50% full load B. at 80% full load D. at full load 87. The frequency of the voltage generated in large alternators  A. 50 Hz C. in kilo cycles B. 60 Hz d. in mega cycles 88. The number of poles in turbo-alternators is usually  A. 2 C. 12 B. 4 D. 50 89. In huge alternators, the moving part is  A. Stator C. Armature B. Poles D. Rotor 90. Harmonic component of generated E.M.F. Will be more in  A. Short pitch coil C. Full pitch coil B. Long pitch coil D. none of above coils 100. The dark and bright lamp method is used for  A. Transfer of load C. Synchronizing B. Balancing of load D. Phase sequence