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EEN 520 – 1EEF EE INTEGRATION COURSE 2 PRELIMINARY EXAMINATION INSTRUCTION: Select the correct answer for each of the following questions. Mark only one answer for each item by shading the box corresponding to the letter of your choice on the answer sheet provided. STRICTLY NO ERASURES ALLOWED. MULT...

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EEN 520 – 1EEF EE INTEGRATION COURSE 2 PRELIMINARY EXAMINATION INSTRUCTION: Select the correct answer for each of the following questions. Mark only one answer for each item by shading the box corresponding to the letter of your choice on the answer sheet provided. STRICTLY NO ERASURES ALLOWED. MULTIPLE CHOICE: 1. An inductance of 8 mH is in series with the parallel combination of 3 mH and 6 mH. What is the equivalent inductance? A. 4 mH B. 6 mH C. 8 mH D. 10 mH 2. The value of mutual inductance in terms of self inductance of the two coils L1 and L2 is proportional to A. L1 L2

B. L1 / L2

C.

D.

3. When one coil of a magnetically coupled pair has a current of 5 A, the resulting fluxes ø 11 and ø12 are 0.4 and 0.8 mWb, respectively. If the turns are N1 = 500 and N2 = 1500, find M. A. 120 mH B. 20 mH C. 240 mH D. 40 mH 4. Ohm’s law is applicable in all DC and AC circuits provided that this parameter does not change. Which one? A. Voltage B. Current C. Resistance D. Temperature 5. An inductance of 40 mH is connected in series with 300 Ω resistance. At t = 0, the energy stored is 0.96 microjoule. Find the current at t = 0. A. 0.44 x 10-3 A B. 0.22 x 10-3 A C. 13.86 x 10-3 A D. 6.93 x 10-3 A 6. Calculate the distance from a normally placed screen a 30 candela lamp be placed in order that the illumination be 5 lux. A. 2.45 m B. 4.45 m C. 5.25 m D. 3.77 m 7. A 50-kVA single-phase transformer has on full-load a copper loss of 560 W and iron loss of 500 W. Calculate the efficiency at 25% of full-load for a power factor of 0.8 lagging. A. 93.9% B. 94.9% C. 95.9% D. 96.9% 8. A three-phase induction motor is taking 40 kW, the slip being 4%, the stator losses amount to 800 watts, calculate the total power developed. A. 39.200 kW B. 40.800 kW C. 37.632 kW D. 36.732 kW 9. An air gap 1.1 mm long and 40 sq. cm in cross-section exists in a magnetic circuit. Determine the mmf required to create a flux of 10 x 10-4 Wb in the air gap.

A. 2.1885 AT

B. 21.885 AT

C. 218.85 AT

D. 2188.5 AT

10. What is the copper loss at full-load of a transformer if its copper loss at 7/8 th full-load is 4900 W? A. 5600 W B. 3750 W C. 6400 W D. 375 W 11. If three transformers in Δ - Δ are delivering rated load and one transformer is removed, then overload on each of the remaining transformers is _____ percent. A. 66.6 B. 173.2 C. 57.7 D. 73.2 12. An impedance 4 – j3 ohms is connected in parallel with an ideal conductor L across a 110 V, 60 Hz mains. Determine L if the total voltage supplied to the circuit will be in phase with the total current drawn. A. 16.6 mH B. 19.2 mH C. 22.1 mH D. 26.8 mH 13. The three unbalanced currents are: I a = 10 cis(-30°), I b = 0, Ic = 10 cis 150°. Find the phase C positive sequence current. A. 5.77 A B. 5.77 cis 120° A C. 8.66 cis 120° A D. 5.77 cis 240° A 14. A coil of inductance 10 H and resistance 2 Ω is supplied at 20 V. Find the average emf induced when the circuit is opened if the current falls to zero in 0.5 sec. A. 20 V B. 10 V C. 100 V D. 200 V 15. A 200 V, three-phase source is connected to two equal impedances of 7.07 + j7.07 ohms in parallel and with both connected in wye configuration. What is the current per phase of the combination? A. -16.26 – j16.26 A B. 16.26 + j16.26 A C. 16.26 – j16.26 A D. -16.26 + j16.26 A 16. A dc machine has 8 poles and a rated current of 100 A. How much current will flow in each conductor at rated condition if the armature is simplex lap wound? A. 6.25 A B. 50 A C. 25 A D. 12.5 A 17. A 2-µF capacitor, with initial charge of 100 µC is connected across a 100 Ω resistor at t = 0. Calculate the time in which the transient voltage across the resistor drops from 40 to 10 volts. A. 27.7 ms B. 0.277 ms C. 2.77 ms D. 277 ms 18. A 400-volt 50 Hz star connected induction motor takes a line current of 50 amperes at a p.f. of 0.8 lagging. Three mesh connected capacitors are connected to raise the p.f. to 0.9. Find the value of each capacitor in microfarads. A. 146.7 B. 48.9 C. 16.3 D. 24.5 19. Two capacitors C1 and C2 are placed in series. If C1 = 100 µF, C2 = 50 µF, find the maximum energy stored when a 220 V dc supply is applied across the combination. A. 0.107 J B. 0.507 J C. 0.807 J D. 1.107 J 20. Two electrons in a vacuum experience a force of 2 x 10 -15 N. How far apart are the electrons? A. 2.84 x 10-12 m B. 3.4 x 10-7 m C. 9.6 x 10-7 m D. 5.68 x 10-12 m 21. It is desired to correct the 2400-kVA 0.65 lagging power factor load in a plant to unity by the installation of a synchronous condenser. Calculate the kVA rating of the latter.

A. 2400

B. 1825

C. 1560

D. 1960

22. For a 36-slot 4-pole three-phase full-pitch distributed winding, what is the percent reduction in the generated voltage? A. 4 B. 3 C. 6 D. 5 23. Three 10:1 transformers are connected Δ / Y for stepping up the 2300-volt three-phase source. Calculate the secondary line voltage. A. 23,000 V B. 69,000 V C. 46,000 V D. 40,000 V 24. What is the device function number of overvoltage relay? A. 59 B. 76 C. 27

D. 67

25. A short 3-ø line with an impedance of 6 + j8 Ω per line has sending and receiving end line voltages of 120 and 110 kV respectively for some receiving end load at a p.f. of 0.9 lagging. The active power at the receiving end is nearest to A. 100,200 kW B. 200,000 kW C. 120, 000 kW D. 110,200 kW 26. Two long straight conductors each carrying an electric current of 5 A, are kept parallel to each other at a separation of 2.5 cm. Calculate the magnitude of magnetic force experienced by 10 cm of a conductor. A. 2 x 10-3 N B. 2 x 10-4 N C. 2 x 10-5 N D. 2 x 10-6 N 27. A solenoid 500 cm long and 10 cm in diameter is wound with 1500 turns. Find the energy stored in the magnetic field when a current of 5 A flows. A. 0.045 J B. 0.055 J C. 0.046 J D. 0.072 J 28. The load of a certain transformer is reduced to 50%, the copper loss would become A. 0.25 times B. 0.50 times C. 2 times D. same as before 29. At a slip of 4% the maximum possible speed of a 3ø, 60 Hz squirrel cage induction motor is A. 3600 rpm B. 3456 rpm C. 3200 rpm D. 3000 rpm 30. An electric heater develops a power of 1 kW when run on 230 V supply. If the resistance wire of the heater has a diameter of 0.5 mm and a resistivity of 60 x 10 -8 -m, find the minimum length of the wire required. A. 11.3 m B. 13.3 m C. 15.3 m D. 17.3 m 31. Each conductor of a horizontally arranged two-conductor bundle line is ACSR, 1272 MCM Pheasant. The spacing between bundle centers is 8 m, 8 m and 16 m and between bundle conductors is 45 cm. Find the inductive reactance of the line in ohms per km per phase if GMR of each conductor is 0.0466 ft. A. 0.165 B. 0.265 C. 0.365 D. 0.465 32. A 4-pole lap-wound armature has 480 conductors and a flux per pole of 25 mWb. What is the emf generated, when running at 600 rpm? A. 240 V B. 120 V C. 60 V D. 30 V

33. Transmission voltage level of 1000 kV is categorized as A. Low Voltage B. High Voltage C. Extra High Voltage

D. Ultra High Voltage

34. A coil of inductance 8 mH, produces 80 µWb of magnetic flux. Of this total flux 60 µWb are linked to a second coil of inductance 2 mH. How much is the mutual inductance between the coils? A. 3 mH B. 4 mH C. 5 mH D. 2 mH 35. An electric heater takes 1.2 kWHR in 30 minutes at 120 V. What is the current input to the heater? A. 20 A B. 15 A C. 10 A D. 5 A 36. When the relative permeability of a material is slightly less than 1, it is called ________ material. A. non-magnetic B. paramagnetic C. ferromagnetic D. diamagnetic 37. The rms value of sinusoidal ac current is equal to its value at an angle of ___ degrees. A. 45 B. 30 C. 90 D. 60 38. A current of 20 A flows through two ammeters A and B joined in series. Across A, the potential difference is 0.2 V and across B, it is 0.3 V. Find how the same current will be divided between the two when they are joined in parallel. A. 10 A, 10 A B. 12 A, 8 A C. 14 A, 6 A D. 16 A, 4 A 39. An office, 17 m by 8 m wide, is lighted by 8 lamps and each lamp has a luminous intensity of 200 Cd. Allowing an absorption loss of 4000 lm for the reflectors, walls and ceiling, calculate the average illuminations on the working plane. A. 147.9 lm/m2 B. 132.6 lm/m2 C. 118.4 lm/m2 D. 112.8 lm/m2 40. Two wattmeters can be used to measure 3-phase power for a A. balanced and unbalanced load C. balanced load only B. unbalanced load only D. unity power factor only 41. Calculate the capacitance between two parallel plates each of which is 100 cm 2 and 2 mm apart in air. A. 0.443 pF B. 0.515 pF C. 0.452 pF D. 0.502 pF 42. A transformer has 4% resistance and 6% reactance drop. Find the voltage regulation at full-load unity power factor. A. 2% B. 3% C. 4% D. 5% 43. The current in a circuit is given by i = 50sinωt. If the frequency be 25 Hz, how long will it take for the current to rise to 25 amp? A. 0.02 sec B. 3.33 x 10-3 sec C. 0.05 sec D. 0.033 sec 44. A single-phase transformer when supplied from 220 V, 50 Hz has eddy current loss of 50 W. If the transformer is connected to a voltage of 330 V, 50 Hz, the eddy current loss will be A. 168.75 W B. 112.5 W C. 75 W D. 50 W

45. The resistance of the field coil of a motor is 200 Ω at 15 °C. After the motor worked for a few hours on full load, the resistance increases to 240 Ω. Calculate the temperature rise of the field coil assuming the temperature coefficient of resistance is 0.0042 per °C at 0 °C. A. 20.6 °C B. 30.6 °C C. 40.6 °C D. 50.6 °C 46. Surge impedance of transmission line is given by A.

B.

C.

D.

47. A single-phase transmission line has a total resistance of 1.5 Ω and a loop reactance of 0.3 Ω. It delivers 2 MW at 11 kV at a power factor of 0.8 lagging. Calculate the line voltage at the sending end. A. 11.21 kV B. 11.11 kV C. 11.41 kV D. 11.31 kV 48. Three 40 Ω non-inductive resistances are connected in delta across 200-V, 3-phase lines. Calculate the power taken from the mains if one of the three resistors is disconnected. A. 500 W B. 1000 W C. 1500 W D. 2000 W 49. Power in a balanced three-phase system is measured by the two wattmeter method and it is found that the ratio of the two readings is 2:1. What is the power factor of the system? A. 0.5 B. 0.8 C. 0.866 D. 1 50. One advantage of secondary cell is that it A. can be recharged B. can be used for portable equipment

C. is compact, easy to carry D. cannot be recharged

51. Calculate the capacitance of a parallel plate capacitor having 20 cm x 20 cm square plates separated by a distance of 1 mm. Assume the dielectric medium to be air. A. 3.54 pF B. 35.4 pF C. 354 pF D. 3540 pF 52. Calculate the self-inductance of an air-cored solenoid, 40 cm long, having an area of cross-section 20 cm2 and 800 turns. A. 2.42 mH B. 4.02 mH C. 5.20 mH D. 6.40 mH 53. A three-phase induction motor having an input power of 30 kW is running at a slip of 4%. The stator loss is 1 kW and friction and windage loss is 1.5 kW. Determine the motor efficiency. A. 86.8% B. 87.8% C. 88.8% D. 89.8% 54. An unshaded lamp is 6 m above the table. It is lowered down by 2 m. By how much is the illumination on the table increased? A. 2 times B. 2.25 times C. 2.5 times D. 2.75 times 55. Find the capacitive susceptance of a single-phase line operating at 60 Hz. The conductor is Partridge with an outside diameter of 0.642 in and spacing is 20 ft between centers. A. 4.10 x 10-6 mho/mile to neutral C. 5.10 x 10-6 mho/mile to neutral

B. 4.90 x 10-6 mho/mile to neutral

D. 5.90 x 10-6 mho/mile to neutral

56. An inductor supplied with 100 V ac with a frequency of 10 kHz passes a current of 10 mA. The value of inductor is A. 1.7 mH B. 16 mH C. 1 mH D. 160 mH 57. Two inductors of 20 mH and 10 mH are connected in series carrying a current of 1 A. Find the stored energy. A. 15 mJ B. 20 mJ C. 30 mJ D. 60 mJ 58. Three capacitors are connected in parallel. C1 = 12 µF, C2 = 10 µF and C3 = 40 µF. What is the total capacitance? A. 45 µF B. 5 µF C. 10 µF D. 62 µF 59. For an ac motor, the frequency is 60 Hz and the speed is 300 rpm. What is the number of poles? A. 26 B. 24 C. 28 D. 30 60. Power in a three-phase delta system with balanced load is equal to A.

B.

C.

D. 61. What is the minimum number of wattmeters required to measure unbalanced power for a threephase system? A. 2 B. 4 C. 3 D. 1 62. The value of form factor for a pure sine wave is A. 1.414 B. 0.707

C. 0.637

D. 1.11

63. Find the horsepower rating of a motor running at 1500 rpm and developing a torque of 105 lb-ft. A. 22 B. 28 C. 30 D. 36 64. There are two wires A and B. If the resistance of B is R and the diameter of A is twice of B, the length and the nature of the material is the same, find the resistance of A. A. R/2 B. R/4 C. 4R D. 2R 65. A wire has a resistance of 1 Ω. If the length is increased four times and the area is doubled the original, find the new resistance of the wire. A. 5 Ω B. 2 Ω C. 1 Ω D. 0.5 Ω 66. Two 30 Ω resistances are connected in series. When an unknown resistance R is connected in parallel with one, the new total resistance is 40 Ω. What is the value of R? A. 5 Ω B. 15 Ω C. 20 Ω D. 25 Ω 67. A 10:1 single-phase transformer is rated 100 kVA, 2400/240 V. When the low voltage side of the transformer is maintained at 240 V, what is the secondary impedance? A. 0.676 Ω B. 0.776 Ω C. 0.576 Ω D. 0.876 Ω

68. What is the counterpart of magnetic flux in an electric circuit? A. voltage B. current C. resistance

D. conductance

69. In a parallel circuit the potential difference across the resistance A. varies C. is sometimes constant B. is different from the applied voltage D. is always constant 70. The rms value of a sinusoidal wave is equal to _______ of maximum value. A. 0.637 B. 0.707 C. 0.506 D. 1.414 71. When one coil of a magnetically coupled pair has a current of 5 A, the resulting fluxes ø 11 and ø12 are 0.4 and 0.8 mWb, respectively. If the turns are N1 = 500 and N2 = 1500, find L2. A. 530 mH B. 540 mH C. 1060 mH D. 1080 mH 72. In two-wattmeter method, the readings of the wattmeters will be identical when A. load in one of the phases is zero C. power factor is 0.5 B. power factor is unity D. neutral is earthed 73. Two electrons have a force of 3.46 x 10 6 N. What is the distance between them? A. 8.1 x 10-7 m B. 1.8 x 10-7 m C. 8.1 x 10-18 m D. 1.8 x 10-18 m 74. A wire 36 inches long is carrying a current of 1200 A. Find the flux density in gauss at a point 12 inches from the wire. A. 2.40 B. 7.87 C. 6.31 D. 5.52 75. Four resistances of 10, 20, 30 and 40 ohms are connected in parallel. What is the equivalent resistance? A. 100 Ω B. 9.6 Ω C. 3.6 Ω D. 4.8 Ω 76. A 120 V dc motor draws 225 A from the supply at a distance of 350 m using two copper conductors of diameter 0.5 inch and resistivity 10.4 ohm-cmil/ft. Find the voltage of the supply. A. 126 V B. 133 V C. 138 V D. 142 V 77. A balanced delta connected load impedance of 15 + j18 Ω per phase is connected across a 230 V, three-phase source. Find the total power consumed. A. 10,580 W B. 1445 W C. 4336 W D. 3527 W 78. 34.5 kV to 69 kV is classified as A. low voltage B. medium voltage

C. high voltage

D. extra high voltage

79. A circuit has a resonant frequency of 4000 rad/sec and bandwidth of 100 rad/sec. If the resistance is 5 ohms, find the value of L and C. A. 50 mH, 1.25 µF B. 1.25 mH, 50 µF C. 5 mH, 12.5 µF D. 12.5 mH, 5 µF

80. A 10 HP, 230 V, 60 Hz three-phase motor has an efficiency of 90% and pf of 0.85 lagging. What is the capacitance per phase in microfarads to be connected in parallel with the motor to correct the power factor to unity? A. 285 µF B. 155 µF C. 25.8 µF D. 15.5 µF 81. Three impedances are in parallel. The currents drawn by the impedances are I a = 10 A, I b = 12 A and I c = 15 A, respectively. If I a is the reference, Ib leads Ia by 30°, and I c leads Ia by 45°, what is the total current? A. 10∠0° + 12∠30° - 15∠45° C. 10∠0° - 12∠30° + 15∠45° B. 10∠0° - 12∠30° - 15∠45° D. 10∠0° + 12∠30° + 15∠45° 82. An aluminum cable has 10 identical strands, a length of 1500 m and a diameter of 2.50 mm each. What is the resistance of the cable? (Resistivity of Al = 17 Ω-CM/ft) A. 5.63 Ω B. 0.563 Ω C. 8.63 Ω D. 0.863 Ω 83. A 40-m metallic conductor of cross-sectional area 1 mm 2 has a resistance of 12 Ω. Calculate the conductivity of the metal. A. 3.33 MS/m B. 0.333 MS/m C. 6.67 MS/m D. 0.667 MS/m 84. The voltage across a 50-µF capacitor rises at a constant rate of 10 V/ms. Calculate the current through the capacitor. A. 2 mA B. 5 mA C. 50 mA D. 500 mA 85. Express the current phasor 25∠-30° as instantaneous current. A. 17.68sin(ωt-30°) B. 35.35sin(ωt+30°) C. 35.35sin(ωt-30°)

D. 25sin(ωt-30°)

86. A 7.5-HP, 500 V three-phase induction motor is developing its full-load output at 960 rpm. The starting torque is equal to the full-load torque. What will be the starting torque if the supply voltage falls to 400 volts? A. 35.62 N-m B. 32.34 N-m C. 28.27 N-m D. 38.82 N-m 87. A light bulb having a tungsten filament, draws 0.5 A at 110 V. The cold resistance of the filament is 20 Ω at 20 °C. At this temperature the temperature coefficient of resistance for tungsten is 0.005 °C-1. Determine the operating temperature of the bulb. A. 1980 °C B. 2080 °C C. 2120 °C D. 2020 °C 88. A single-circuit three-phase line operated at 60 Hz is arranged in a triangular configuration with distances of 20 ft, 20 ft and 38 ft between conductors. The conductors are ACSR Drake with GMR of 0.0373 ft. Find the inductive reactance per mile per phase. A. 0.478 Ω B. 0.578 Ω C. 0.788 Ω D. 0.678 Ω 89. A 120-V shunt motor has an armature equivalent of 0.5 Ω and a field resistance of 60 Ω. At full-load, the motor takes 10 A and the speed is 1000 rpm. At what speed must this motor may be driven as a generator to deliver 10 A to an external load at 120 V? A. 1158 rpm B. 1086 rpm C. 1262 rpm D. 1045 rpm 90. The terminal voltage of a Y-connected load consisting of three equal impedances of 20 ∠30° Ω is

4.4 kV line to line. The impedance in each of the three lines connecting the load to a bus at a substation is ZL = 1.4∠75° Ω. Find the line to line voltage at the substation bus. A. 4.52 kV B. 4.62 kV C. 4.48 kV D. 4.58 kV

91. The reactance of a generator designated X” is given as 0.25 per unit based on the generator’s nameplate rating of 18 kV, 500 MVA. The base for calculations is 20 kV, 100 MVA. Find X” on the new base. A. 0.0405 pu B. 0.0504 pu C. 0.0450 pu D. 0.0540 pu 92. If the voltage is doubled, the ampacity of a conductor A. increases B. decreases C. doubles

D. remains the same

93. A three-phase alternator has 6 slots per pole per phase. Determine the distribution factor. A. 0.977 B. 0.956 C. 0.963 D. 0.948 94. As the load is increased the speed of a dc shunt motor will A. remain constant C. increase proportionately B. increase slightly D. reduce slightly 95. A 50 HP, 440 V, 3-phase, 60 Hz, 6-pole squirrel cage induction motor is operating at full-load and 0.8 power factor. The full-load efficiency is 85% and the percentage slip is 5%. Determine the full-load torque. A. 214.55 N-m B. 206.72 N-m C. 312.47 N-m D. 323.24 N-m 96. A 170-mile, 230-kV, 60 Hz, three-phase single-circuit transmission line uses a triangular arrangement with 20 ft, 20 ft and 36 ft spacing, respectively. If the line conductors have a GMR of 0.0217 ft, determine the capacitive susceptance to neutral per mile. A. 4.81 x 10-6 mho per mile C. 7.92 x 10-6 mho per mile -6 B. 12.74 x 10 mho per mile D. 2.47 x 10-6 mho per mile 97. A series RLC circuit has R = 100 ohms, L = 100 µH and C = 100 pF. What is the frequency in MHz at unity power factor? A. 1.59 B. 1.36 C. 15.9 D. 13.6 98. An impedance draws a current of i = 10cos(ωt-30°) A from a supply with voltage e = 220sinωt V. What is the impedance in ohms? A. 11 + j19.05 B. 11 - j19.05 C. 19.05 + j11 D. 19.05 - j11 99. A balanced wye-connected load with resistance of 8 ohms per phase and no reactance is supplied by a 240 V, 3-phase source. Find the real power of the load in watts. A. 6400 B. 720...