EE REFRESHER 1

1. Find the current in a conductor through which 2.5x1020 free electrons pass in 8 seconds.A. 3 A C. 2 AB. 5 A D. 7 A

2. Calculate the resistance of a hard – drawn copper wire having a radius of 0.125 in and a length equal to 10 ft.A. 1.6592 mΩ C. 1.704 mΩB. 2.6342 mΩ D. 2.220 mΩ

3. A 6 Ω resistor is connected in series to a parallel connection of a 30 Ω resistor and a variable resistor R. What must be the value of R such that the power taken by the 6 Ω resistor will be equal to the power taken by R?A. 14.98 Ω C. 12.58 ΩB. 9.45 Ω D. 11.46 Ω

4. A resistor and an inductor are connected in parallel to a 120 V, 60 Hz source. If the total current and power in the circuit are respectively 17 A and 1800 W, find the value of L.A. 0.0398 H C. 0.0455 HB. 0.0284 H D. 0.0338 H

5. A voltage wave is given by e = 100 sin 314t. How long does it take this waveform to complete one-fourth cycle?A. 2 ms C. 8 msB. 5 ms D. 4 ms

6. A current of 5 A flows through a resistance in series with a choking coil when applied at 250 – V, 60 Hz. If the voltage across the resistance is 125 volts and across the coil is 200 volts, determine the inductance of the coil.A. 0.124 H C. 0.222 H B. 0.102 H D. 0.454 H

7. The equation of an alternating emf is e = 155sin(157t + 30°) V. What is value of t in seconds when e first reaches a maximum negative value?A. 0.027 sec C. 0.086 secB. 0.052 sec D. 0.061 sec

8. A unity power factor load of 1794 watts is connected in parallel with a load of 1656 watts operating at a lagging pf of 0.6. If the line voltage is 115 V, calculate the total current.A. 28.55 A C. 32.23 AB. 41.72 A D. 35.62 A

9. An impedance load consisting of 12 ohms resistance and 16 ohms inductive reactance is connected across a 60 Hz, 100 V source. Find the capacitance of the condenser which may be paralleled with this load to bring the power factor to 0.8 lagging.A. 61.33 µF C. 53.45 µFB. 38.79 µF D. 46.42 µF

10. A single phase motor is rated 5 hp, 75% pf and 220 volts. What is the approximate size of the capacitor necessary to raise the power factor to about 95%?

A. 1.055 kVAR C. 2.063 kVARB. 2.521 kVAR D. 3.445 kVAR

11. If Van = 200∠40˚ volts, determine VAC. A. 200√3∠160˚ V C. 200√3∠-200˚ VB. 200√3∠-170˚ V D. 200√3∠10˚ V

12. A balanced three – phase connected load draws 20 kW at a power factor of 0.4. The frequency is 60 Hz. If the line voltage at the load terminals is 1,300 V, calculate the value of each capacitance for delta connection.A. 28.544 microfarad C. 30.776 microfaradB. 25.863 microfarad D. 22.523 microfarad

13. A balanced delta connected load, with impedance 10 -36.9° Ω, and a balanced Y – connected load ∠are supplied by the same three phase ABC system having Vca = 141.4 240° V. If the current in line A ∠is 40.44 133.41° A, what are the impedances of the∠ Y – connected load?A. 5cis-60° Ω C. 4cis-30° ΩB. 5cis-53.3° Ω D. 4cis-66.7° Ω

14. A factory is supplied by a three – phase, three – wire system with the following characteristics.

VAB = 230cis0° V IA = 110cis-36.87° AVBC = 230cis240° V IC = 125cis53.13° A

Determine the average power factor of the load.A. 0.878 lagging C. 0.851 laggingB. 0.922 lagging D. 0.934 lagging

15. Determine the operating power factor of a three phase balanced load if the readings of the two wattmeters properly connected to measure power is 3:1A. 0.866 C. 0.778 B. 0.756 D. 0.922

16. Given a balanced 3-wire, three phase system serving the following loads:

Vab = 200cis0° VZab = 10cis53.13° ΩVbc = 200cis240° V Zbc = 10 Ω Vca = 200cis120° V Zca = 10cis30° Ω

Determine the current on line b.A. 20.34 A C. 24.36 AB. 22.04 A D. 21.57 A

17. A load is supplied by a three phase, 3 wire system with the following characteristics:

Vab = 230cis0° V Ia = 110cis-36.87° AVbc = 230cis240° V Ic = 125cis53.13° A

Determine the power consumed by the load.A. 45.12 kW C. 48.78 kWB. 41.55 kW D. 47.98 kW

18. A 240 – V three phase system supplies a 100 kW, 0.6 lagging balanced load. Determine the capacitance in each phase of a wye – connected capacitor bank in order to adjust the power factor to 0.95 lagging.A. 4.63 F C. 5.3 FB. 11.10 mF D. 100.47 mF

19. In a balanced star-connected system, the line voltages are __ ahead of their respective phase voltages.A. 30° C. 120°B. 60° D. 45°

20. A three – phase motor takes 10 kVA at 0.6 power factor lagging from a source of 220 V. It is in parallel with a balanced delta connected load having 16 ohm resistance and –j12 reactance in series with each phase. Find the total kVAR of the combination.A. 8.43 C. 3.64 B. 12.35 D. 15.33

21. A 3-phase 50-HP, 440 V 60-Hz induction motor operates on full load with an efficiency of 80% and a power factor of 0.85 lagging. It is required to raise the full load power factor 0.95 lagging by using capacitor bank connected in delta. What will be the capacitance per phase in microfarads?A. 61.98 µF C. 53.48 µFB. 52.58 µF D. 63.63 µF

22. Consider two point charges of +q and +4q which are separated by a distance of 3 meters. At what point (from +q) on the line joining the two charges, is the electric field equal to zero?A. 1 m C. 3 mB. 2 m D. 2.5 m

23. Charge one of +4 µC is located at (2, 0, 0). Charge two of -5 µC is located at (0, 0, 2). What is the force between them?A. 0.0823 N C. 0.0225 NB. 0.067 N D. 0.055 N

24. The energy stored in a 3.6 µF capacitor with an applied voltage of 15 volts isA. 0.634 mJ C. 0.405 mJ B. 0.3 mJ D. 0.556 mJ

25. The wing span of a metal airplane is 36 m. If the plane is flying at 400 kph, determine the emf induced between the wingtips. Assume that the vertical component of the earth’s magnetic field is 40 µT.A. 0.20 V C. 0.18 VB. 0.57 V D. 0.16 V

26. A conductor of 150 cm moves at an angle of 30° to a uniform magnetic field of strength 0.8 Tesla with a velocity of 30 m/s. Determine the induced emf.A. 20 V C. 36 VB. 18 V D. 30 V

27. A short shunt compound generator has a full load current of 60 A. If the series field resistance is 0.04 Ω and the diverter carries 24 A, calculate the diverter resistance. A. 0.06 Ω C. 0.01 ΩB. 0.04 Ω D. 0.02 Ω

28. A 4-pole wave wound dc generator has 50 slots and 24 conductors per slot. The flux per pole is 10 mWb. Determine the induced emf in the armature, if it is rotating at a speed of 600 rpm.A. 240 V C. 120 VB. 200 V D. 180 V

29. A 10 kW long shunt compound generator has a load voltage of 230 V. The shunt field has 800 turns per pole and the series field has 8 ½ turns per pole. The shunt field and series field resistances are 80 Ω and 0.07 Ω, respectively. To make the generator flat compounded, the series field must produce 225 ampere – turns. Calculate the diverter resistance to accomplish this change.A. 0.033 Ω C. 0.069 ΩB. 0.093 Ω D. 0.054 Ω

30. A 150 hp, 600 V, 205 A, shunt motor is running at 1700 rpm full load. The resistance of the shunt field circuit is 240 Ω and the total armature circuit resistance is 0.15 Ω. Calculate the speed regulation of the motor.A. 5.08% C. 5.28%B. 5.18% D. 5.38%

31. A 90-slot stator has a 3-phase, six pole winding. Each coil spans from slot 1 to slot 14. Calculate the armature –winding distribution factor.A. 0.978 C. 0.936B. 0.957 D. 0.927

32. From the previous problem, calculate the winding factor.A. 0.867 C. 0.936B. 0.957 D. 0.978

33. A 3 phase wye connected 1000 kVA, 2300 V alternator is short circuited & operated at rated speed to produce rated current. With the short circuit removed and the same excitation, the voltage between terminals is 1300 V. The effective armature resistance between terminals is 2 ohms. Determine the per cent regulation at a power factor of 0.8 lagging.A. 54.4 % C. 50.37 % B. 57.34 % D. 56.69 %

34. Calculate the pitch factor for an alternator winding with 72 slots, 6-poles, and coil span of 1 to 10.A. 0.8934 C. 0.9239 B. 0.9428 D. 0.9750

35. Two alternators operating in parallel supply the following loads: A =400 kW, unity pf; B=1000 kW, 0.707 lagging pf; C= 600 kW, 0.90 leading pf. One machine supplies 800 kW at 0.866 lagging power factor. What is the power factor of the other machine?A. 0.983 lagging C. 0.979 laggingB. 0.971 lagging D. 0.908 lagging

36. A wye – connected, 1000 kVA, 11 kV synchronous motor has a synchronous impedance of (3.5 + j40) ohms. When fully loaded at 0.80 lagging power factor, the induced emf between lines is nearest toA. 5899 V C. 9872 VB. 8985 V D. 1029 V

37. A single phase transformer has a net core area of 60 cm2. The primary having 400 turns is connected to a 550 – volt supply. What is the flux density in the core? The supply frequency is 60 Hz.A. 0.78 T C. 0.94 TB. 0.86 T D. 1.08 T

38. A 400 MVA, 240 kV/24 kV, three phase wye – delta transformer has an equivalent series impedance of 1.2 + j6 ohms per phase referred to the high voltage side. The transformer is supplying a three phase load of 400 MVA, 0.8 pf lagging at a terminal voltage of 24 kV (line to line) on its low voltage side. The primary is supplied from a feeder with an impedance of 0.6 + j1.2 ohms per phase. Determine the line to line voltage at the sending end of the feeder.A. 247.09 kV C. 244.687 kVB. 249.09 kV D. 243.221 kV

39. When “a” is the operator, a – a2 is equal to _____.A. 0 C. 1B. -1 D. j (sqrt of 3)

40. A load of 25 MW, 0.8 pf lagging is delivered by a three – phase supply having a resistance per phase per km equal to 0.5576. If the load voltage is 132 kV between lines and the losses in the transmission line is 7.5% of the load, calculate the distance over which the load can be delivered. A. 50 km C. 60 kmB. 55 km D. 65 km

41. In a three – phase transmission conductors are arranged at the corners of an equilaline, the teral triangle of each side 2.5 m. If the radius of each conductor is 0.8 cm, determine the inductance per phase per kilometre length of the line.A. 1.2 mH/km C. 2.4 mH/kmB. 3.5 mH/km D. 5.5 mH/km

42. Medium transmission lines are up to ____ km.A. 80 C. 240B. 200 D. 300

43. A 50 MVA, 33 kV/11 kV, three phase, wye – delta connected transformer has a 3 % impedance. What is the per cent impedance at 100 MVA base and 34.5 kV base?A. 5.02 % C. 5.49 % B. 6.92 % D. 6.24 %

44. Determine the three phase fault current in a power system that has a positive, negative, and zero sequence reactances of 0.5 pu, 0.5 pu, and 0.26 pu, respectively. kV and MVA bases are 115 and 100.A. 1004 A C. 8006 AB. 4001 A D. 6008 A

45. A 4x4 Z – bus matrix has the following per cent impedances corresponding to each element: Z11 = j0.11 pu, Z12 = j0.18 pu, Z13 = j0.12 pu, Z14 = j0.24 pu, Z21 = j0.21 pu, Z22 = j0.18 pu, Z23 = j0.16 pu, Z24 = j0.24 pu, Z31 = j0.43 pu, Z32 = j0.14 pu, Z33 = j0.3 pu, Z34 = j0.56 pu, Z41 = j0.72 pu, Z42 = j0.17 pu, Z43 = j0.13 pu, Z44 = j0.25 pu. Calculate the three – phase fault of the power system if the fault occurs on bus 4 of the system. Base MVA and Base kV are 200 and 13.8, respectively. A. 33.5 kA C. 29.2 kAB. 47.2 kA D. 51.8 kA

46. The positive, negative, and zero sequence reactances of a 20 MVA, 13.2 kV synchronous generator are 0.3 pu, 0.2 pu, and 0.1 pu., respectively. The generator is solidly grounded and is not loaded. If a double line to ground fault occurs at the generator terminals b and c, determine the line voltage Vab.A. 4.16 kV C. 6.72 kVB. 7.62 kV D. 5.35 kV

SITUATION: A synchronous generator rated at 20 MVA, 13.8 kV has the following subtransient reactances:

X1 = j0.25 puX2 = j0.35 puX0 = j0.10 pu

The machine has a bolted fault and the neutral is solidly grounded.

47. Determine the three – phase fault.A. 3586 A C. 5956 AB. 3347 A D. 2415 A

48. Calculate the single line to ground fault.A. 3586 A C. 5956 AB. 3347 A D. 2415 A

49. Calculate the line to line fault.A. 3586 A C. 5956 AB. 3347 A D. 2415 A

50. Determine the double line to ground fault.A. 3586 A C. 5956 A B. 3347 A D. 2415 A