EE August 15, 2021

Question 1

2. A washing machine is, in effect, an R-L circuit. If the machine takes 311 W and 4.5 A from a 155-V source when operating normally. Find its power factor. *
3. 75 lagging
4. 65 lagging
5. 60 lagging
6. 70 lagging

Answer 1

0.60 lagging

Question 2

4. Approximately how far away must an isolated positive point charge of 1 x 10^(–8) C be in order for it to produce an electric potential of 100 V? The charge is in free space with e = 8.85 x 10^(–12) C^2/N*m^2. *
5. 6 m
6. 2 m
7. 90 m
8. 3 m

Answer 2

0.90 m

Question 3

6. Three single-phase transformers rated 25 kVA each are connected in delta-delta to supply a balanced load of 75 kVA. One transformer is removed for repair, what is the kVA of each remaining transformer? *

57.7
50
43.3
34.3

Answer 3

43.3

Question 4

8. The per phase line loss in a 40 km long transmission line is NOT to exceed 60 kW while it is delivering 100 A per phase. If the resistivity of the conductor material is 1.72 x 10-8 ohm-meter, determine the required conductor diameter. *
9. 2071 cm
10. 1721 cm
11. 2083 cm
12. 2204 cm

Answer 4

1.2083 cm

Question 5

11.	The dc armature winding resistance between terminals of a 750 kVA, 4400 volt, three-phase alternator is 0.9 ohm. Calculate the copper loss in the winding at full-load. *
13,075 W
16,343 W
10,800 W
26,149 W

Answer 5

16,343 W

Question 6

19. A hermetic motor compressor has a rated load current of 25 A. What is the allowable rating for branch disconnecting means? *

31.25 A
28.75 A
30 A
37.5 A

Answer 6

28.75 A

Question 7

28. Three impedances Z₁ = 2.2 + j2.2 Ω, Z₂ = 10 + j10 Ω and Z₃ = −j5 Ω are connected in series. The voltage across Z₁ is 26.59 − j4.69 V. What is the total voltage? *

93 + j62.4 V
93 − j62.4 V
112 − j51 V

Answer 7

112 − j51 V

Question 8

39.	If the current in the armature of a dc series motor is reduced by 50%, the torque of the motor will be reduced by \_\_\_\_\_ % of the previous value. *
25
50
33
75

Answer 8

75

Question 9

40. Find the power factor of a balanced three-phase load in an ABC circuit in which one line voltage is Vac = 440∠−90° v- and one-line current to the load is Ib = 2∠−90° A. *
    0.5 lagging
    0.5 leading
    0 lagging
    0 leading

Answer 9

0 leading

Question 10

42. The following data were obtained when a short-circuit test was performed upon a 100-kVA 2,400/240-volt distribution transformer: Esc = 72 volts; Isc = 41.6 A, Psc = 1,180 watts. What is the equivalent reactance as referred to the secondary? *
43. 0173 Ω
44. 73 Ω
45. 59 Ω
46. 0159 Ω

Answer 10

0.0159 Ω

Question 11

45. What is the capacitance per kilometer of two parallel wires 7 mm in diameter placed 30 cm apart from each other in air? *

625 x 10⁻⁹ F/km

62. 5 x 10⁻⁹ F/km
63. 25 x 10⁻¹² F/km
64. 25 x 10⁻⁹ F/km

Answer 11

6.25 x 10⁻⁹ F/km

Question 12

Two generators G₁ and G₂ are rated 15 MVA, Z equals 0.10, 11 kV and 10 MVA, Z equals 0.10, 11 kV, respectively. The generators are connected to a transformer of 15 MVA, 11 per 66 kV and 6 percent impedance. Calculate the fault current in per unit when three-phase fault occurs on the high voltage side of the transformer. *

12. 5
13. 9
14. 2
15. 33

Answer 12

8.33

Question 13

A balanced three-phase three-wire system has a delta connected load with a 50 ohm resistor, a 5 microfarad capacitor and a 0.56 H inductor in series in each phase. If Van = 390 v rms with 30 deg angle and ω = 500 rad/sec, find the line current to phase c. *
8.308 − j3.462 A
−8.308 + j3.462 A
−7.152 − j5.464 A
−1.158 − j8.925

Answer 13

−7.152 − j5.464 A

Question 14

A 3ϕ transmission line has two aluminum conductors in bundle. The self GMD of each conductor is 8.90 mm and the distance between the conductors and phases is 40 cm and 9 m, respectively. What is the inductance of the line per phase? *
1 μH/m
2 μH/m
3 μH/m
4 μH/m

Answer 14

1 μH/m

Question 15

A three-phase transformer is rated 25 MVA, 69/13.2 kV. It has a series Z = 7%. What is the new per unit impedance if the system study requires 100 MVA base and 67 kV base? *

7. 4%
8. 7%
9. 8 %
10. 9%

Answer 15

29.7%

Question 16

. A hydroelectric generating station is supplied from a reservoir of capacity 5 × 10⁶ cubic meters at a head of 200 meters. Find the total energy available in KWHR if the overall efficiency is 75%. *

2. 725 × 10⁶ kwhr
3. 044 × 10⁶ kwhr
4. 450 × 10⁶ kwhr
5. 088 × 10⁶ kwhr

Answer 16

2.044 × 10⁶ kwhr

Question 17

A 50-kVA, 7,620/240 v, single-phase transformer has rated core loss of 350 watts and rated full-load copper loss of 800 watts. The transformer is 50% loaded for 12 hours at 0.8 p.f. lagging. The rest of the day, it is disconnected from the source. Calculate the all-day efficiency of the transformer. *

97. 32%
98. 32%
99. 32%
100. 32%

Answer 17

97.32%

Question 18

Two identical coupled coils have an equivalent inductance of 40 mH when connected in series aiding and 17.5 mH in series opposing. What is the value of the mutual inductance? *

0. 5625 mH
1. 625 mH
2. 5 mH
3. 25 mH

Answer 18

5.625 mH

Question 19

Two small charged objects attract each other with a force F when separated by a distance d. If the charge on each object is reduced to one-fourth of its original value and the distance between them is reduced to d/2 the force becomes: *
F/16
F/8
F/4
F/2

Answer 19

F/4

Question 20

A nichrome wire is 1 m long and 1 × 10⁻⁶ m² in cross-sectional area. When connected to a potential difference of 2 V, a current of 4 A exists in the wire. The resistivity of this nichrome is: *
1 × 10⁻⁷ Ω·m
2 × 10⁻⁷ Ω·m
4 × 10⁻⁷ Ω·m
5 × 10⁻⁷ Ω·m

Answer 20

5 × 10⁻⁷ Ω·m

Question 21

Two long straight wires are parallel and carry current in the same direction. The currents are 8.0 and 12 A and the wires are separated by 0.40 cm. The magnetic field in tesla at a point midway between the wires is: *
0
12 × 10⁻⁴
8.0 × 10⁻⁴
4.0 × 10⁻⁴

Answer 21

4.0 × 10⁻⁴

Question 22

. A process equipment contains 100 gallons of water at 25°C. It is required to bring it to boiling in 10 minutes. The heat loss is estimated to be 5%. What is the kW rating of the heater? *
125 kW
50.5 kW
252 kW
207 kW

Answer 22

207 kW

Question 23

A 50 HP, 550 V shunt-wound motor draws a line current of 4.5 A at no-load. The shunt field full-load. *
88%
90%
91%
89%

Answer 23

90%

Question 24

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

0. 820 lagging
1. 804 lagging
2. 834 lagging
3. 813 lagging

Answer 24

0.813 lagging

Question 25

A 6-pole, 3-phase, 60 cycle alternator has 12 slots per pole and four conductors per slot. The winding is 5/6 pitch. There are 2,500,000 Maxwells entering the armature from each North Pole, and this flux is sinusoidally distributed along the air gap. The armature coils are all-connected in series. The winding is wye connected. Determine the open circuit emf of the alternator. * 532. 1 V 504. 2 V 572. 4 V 512. 4 V

Answer 25

512.4 V

Question 26

``` A 200 kVA transformer has an iron loss of 1 kW and full-load Cu loss of 2 kW. Its load kVA corresponding to maximum efficiency is _____ kVA. * 100 50 200 141.4 ```

Answer 26

141.4

Question 27

``` . A certain power plant has a reserve capacity above the peak load of 10 MW. The annual factors are load factor = 59%, capacity factor = 41% and use factor = 46%. Determine hours per year not in service. * 937 hours 965 hours 924 hours 952 hours ```

Answer 27

952 hours