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<=KNEC Diploma in Electrical and Electronics Engineering Module II: Electrical Power Generation, Transmission and Protection past paper July 2019
A three phase, 30 MVA, 12 kV alternator has internal reactance of 6% and negligible resistance. Calculate the external percentage reactance to be connected in series with the alternator so that a steady current on short-circuit does not exceed six times the full load current
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Questions List:
1. State two disadvantages and one advantage of diesel power station over geothermal power station.
2. Kenya expects to start generating electricity from nuclear power by the year Explain three factors considered when selecting the site for a nuclear power station.
3. Draw a labelled diagram showing the various penstock protective devices as used in hydro-electric power plant.
4. A diesel power station has fuel consumption of 0.26 kg per kwh. The calorific value of fuel used is 12,000 KCal/kg. Determine the overall efficiency of generation of power
5. With reference to power generation, differentiate between fixed and running costs
6. State four advantages of interconnected grid system in power supply systems
7. Explain the effect of diversity factor on cost of generation of electric power
8. A power generating station has a maximum demand of 40 MW, load factor of 55% and plant capacity factor of 40%. Determine the: (i) daily energy produced; ii)reserve capacity of the plant.
9. Name three types of faults that occur in underground cables
10. With aid of a diagram, describe how to locate ground fault using the varley loop test
11. Data for a 20 kV, 50 Hz, and single core lead sheathed paper insulated cable is as follows: Conductor diameter 30 mm . Internal diameter of lead sheath 60 mm . Conductor length 1.8 km . Insulation permittivity is 3 . Dielectric loss angle 0.0017 radians Determine the: (i) capacitance; (ii) total dielectric loss; (iii) Maximum stress
12. Name three line supports used in overhead transmission lines
13. With the aid of a diagram, show that the expression for inductance L of a single phase overhead line is given by: Where: d = spacing between conductors r = radius of the conductor l = length of the transmission line
14. State three equipment used for improving power factor
15. A sub-station power transformer supplies 400 kW at 0.6 power factor lagging. (I) Sketch the phasor diagram and (II) Calculate the KVAr rating of loss-free static capacitors required to raise the power factor to 0.95 lagging.
16. State four types of electrical short circuits in three phase four wire electrical power systems.
17. State three advantages of sulphur hexafluoride gas circuit breakers over air blast circuit breakers
18. Draw a diagram showing the parts of a high rapturing capacity fuse
19. A three phase, 30 MVA, 12 kV alternator has internal reactance of 6% and negligible resistance. Calculate the external percentage reactance to be connected in series with the alternator so that a steady current on short-circuit does not exceed six times the full load current
20. Explain the function of the following elements in an excitation system: i) Regulator. ii) exciter (iii) power system stabilizer.
21. State three factors that affect cable rating
22. A two-core copper cable supplies current to a 220 V single phase load of 10 kW at 0.8 power factor lagging. The cable is 0.06 km long and the conductor resistance is 0.032Ω . The resistivity of copper is 17.5 μΩ mm. Determine the: (i) cross-sectional area of each conductor; (ii) voltage drop in the cable.
23. Draw the wiring diagram for a final circuit serving three lights each controlled by a single pole switch
24. State six types of building structures
25. Define the following terms as used in illumination and state the units in each case: (i) luminous flux ii)illuminance.
26. With aid of a diagram, describe the operation of low pressure sodium vapour lamp
27. Define Division O area with reference to hazardous areas
28. An electrical workshop measuring 25 m x 12 m is to be illuminated by 150 watt lamps. Illumination required is 60 lúx and lamp efficiency is 16.25 lm/W. If the depreciation factor is 1.3 and utilization factor is 0.5, calculate the number of lamps to be used.
29. Explain three ways of preventing corrosion in electrical installations
30. With aid of a diagram, describe the operation of cathodic impressed current
31. Describe the following parts of a lighting protection system: (I) earth termination; (II) earth electrode.
32. Outline three effects of lightning strokes
1. State two disadvantages and one advantage of diesel power station over geothermal power station.
2. Kenya expects to start generating electricity from nuclear power by the year Explain three factors considered when selecting the site for a nuclear power station.
3. Draw a labelled diagram showing the various penstock protective devices as used in hydro-electric power plant.
4. A diesel power station has fuel consumption of 0.26 kg per kwh. The calorific value of fuel used is 12,000 KCal/kg. Determine the overall efficiency of generation of power
5. With reference to power generation, differentiate between fixed and running costs
6. State four advantages of interconnected grid system in power supply systems
7. Explain the effect of diversity factor on cost of generation of electric power
8. A power generating station has a maximum demand of 40 MW, load factor of 55% and plant capacity factor of 40%. Determine the: (i) daily energy produced; ii)reserve capacity of the plant.
9. Name three types of faults that occur in underground cables
10. With aid of a diagram, describe how to locate ground fault using the varley loop test
11. Data for a 20 kV, 50 Hz, and single core lead sheathed paper insulated cable is as follows: Conductor diameter 30 mm . Internal diameter of lead sheath 60 mm . Conductor length 1.8 km . Insulation permittivity is 3 . Dielectric loss angle 0.0017 radians Determine the: (i) capacitance; (ii) total dielectric loss; (iii) Maximum stress
12. Name three line supports used in overhead transmission lines
13. With the aid of a diagram, show that the expression for inductance L of a single phase overhead line is given by: Where: d = spacing between conductors r = radius of the conductor l = length of the transmission line
14. State three equipment used for improving power factor
15. A sub-station power transformer supplies 400 kW at 0.6 power factor lagging. (I) Sketch the phasor diagram and (II) Calculate the KVAr rating of loss-free static capacitors required to raise the power factor to 0.95 lagging.
16. State four types of electrical short circuits in three phase four wire electrical power systems.
17. State three advantages of sulphur hexafluoride gas circuit breakers over air blast circuit breakers
18. Draw a diagram showing the parts of a high rapturing capacity fuse
19. A three phase, 30 MVA, 12 kV alternator has internal reactance of 6% and negligible resistance. Calculate the external percentage reactance to be connected in series with the alternator so that a steady current on short-circuit does not exceed six times the full load current
20. Explain the function of the following elements in an excitation system: i) Regulator. ii) exciter (iii) power system stabilizer.
21. State three factors that affect cable rating
22. A two-core copper cable supplies current to a 220 V single phase load of 10 kW at 0.8 power factor lagging. The cable is 0.06 km long and the conductor resistance is 0.032Ω . The resistivity of copper is 17.5 μΩ mm. Determine the: (i) cross-sectional area of each conductor; (ii) voltage drop in the cable.
23. Draw the wiring diagram for a final circuit serving three lights each controlled by a single pole switch
24. State six types of building structures
25. Define the following terms as used in illumination and state the units in each case: (i) luminous flux ii)illuminance.
26. With aid of a diagram, describe the operation of low pressure sodium vapour lamp
27. Define Division O area with reference to hazardous areas
28. An electrical workshop measuring 25 m x 12 m is to be illuminated by 150 watt lamps. Illumination required is 60 lúx and lamp efficiency is 16.25 lm/W. If the depreciation factor is 1.3 and utilization factor is 0.5, calculate the number of lamps to be used.
29. Explain three ways of preventing corrosion in electrical installations
30. With aid of a diagram, describe the operation of cathodic impressed current
31. Describe the following parts of a lighting protection system: (I) earth termination; (II) earth electrode.
32. Outline three effects of lightning strokes
