EX-404 Power System-I - Dec 2024 Question Paper

Under each question, How to answer lists the points an answer should cover, outlined by CampusPrep from the syllabus. Check the details against your textbook.

1. 7 Marks
   aWhat are meant by renewable energy sources?
   How to answer

   • Definition of renewable energy sources
   • List of examples - solar, wind, hydro, biomass, geothermal
   • Characteristic of replenishability vs non-renewable
2. 7 Marks
   bDerive the expression for power developed due to wind. Discuss the advantages and disadvantages of horizontal and vertical axis wind mill.
   How to answer

   • Derivation of wind power $P = \frac{1}{2}\rho A V^3$
   • Steps with kinetic energy and mass flow rate
   • Advantages of horizontal and vertical axis wind mill
   • Disadvantages of horizontal and vertical axis wind mill
3. 7 Marks
   aClassify the types of loads and draw their characteristics and explain in detail.
   How to answer

   • Classification of loads - domestic, commercial, industrial, agricultural etc.
   • Load characteristics curves
   • Explanation of each type with load factor and demand
4. 7 Marks
   bA generating station has a connected load of 45 MW and a maximum demand of 20 MW; the units generated being $61.5 \times 10^6$ per annum. Calculate:

   1. i)The demand factor
   2. ii)Load factor
   How to answer

   • Formula for demand factor = maximum demand / connected load
   • Formula for load factor = average load / maximum demand
   • Calculation using $61.5 \times 10^6$ kWh per annum
   • Numerical values of demand factor and load factor
5. 7 Marks
   aDerive an expression for the inductance per phase for a 3-phase overhead transmission line when conductors are symmetrically placed and unsymmetrically spaced.
   How to answer

   • Flux linkages of conductor in 3-phase line
   • Expression for symmetrical spacing
   • Expression for unsymmetrical spacing with transposition
   • Final inductance per phase $L = 2 \times 10^{-7} \ln(D_m/D_s)$
6. 7 Marks
   bCalculate the inductance and capacitance of a 100 km long 3-phase, 50 Hz overhead transmission line consisting of 3 conductors, each of diameter 2 cm and spaced 2.5 m at the corners of an equilateral triangle.
   How to answer

   • Given diameter 2 cm and spacing 2.5 m equilateral
   • Formula for inductance $L = 2\times10^{-7}\ln(D/r')$ per m
   • Formula for capacitance $C = 2\pi\epsilon_0/\ln(D/r)$ per m
   • Multiply by 100 km length
7. 7 Marks
   aDistinguish between the advantages and disadvantages of underground cable over overhead lines.
   How to answer

   • Advantages of underground cable - appearance, safety, low faults
   • Disadvantages - high cost, difficult fault location
   • Comparison with overhead lines on cost, maintenance, voltage level
8. 7 Marks
   bThe maximum and minimum stresses in the dielectric of a single core cable are 40 kV/cm (r.m.s.) and 10 kV/cm (r.m.s.) respectively. If the conductor diameter is 1 cm, Find:

   1. i)Thickness of insulation
   2. ii)Operating voltage
   How to answer

   • Relation $g_{max}/g_{min} = D/d$ for single core cable
   • Use conductor diameter 1 cm to find insulation thickness
   • Formula for operating voltage $V = g_{max} r \ln(D/d)$
   • Numerical values
9. 7 Marks
   aDerive the expression for voltage regulation and transmission efficiency of medium transmission line.
   How to answer

   • ABCD constants for medium line nominal T and Pi
   • Definition of voltage regulation
   • Expression for transmission efficiency
   • Phasor diagram
10. 7 Marks
    bA 3-phase, 50-Hz overhead transmission line 100 km long has the following constants: Resistance/km/phase $= 0.1 \Omega$ Inductive reactance/km/phase $= 0.2 \Omega$ Capacitive susceptance/km/phase $= 0.04 \times 10^{-4}$ siemen. Determine: Use nominal T method.

    1. i)The sending end current
    2. ii)Sending end voltage
    3. iii)Sending end power factor
    4. iv)Transmission efficiency when supplying a balanced load of 10,000 kW at 66 kV, p.f. 0.8 lagging.
    How to answer

    • Calculate total R, X, Y for 100 km
    • Nominal T circuit analysis for sending end voltage and current
    • Calculation of sending end power factor
    • Efficiency = receiving power / sending power
11. 7 Marks
    aExplain with neat sketch, the different types of insulators.
    How to answer

    • Pin, suspension, strain, shackle insulators
    • Neat sketches of each type
    • Application voltage levels
    • Properties of insulator material
12. 7 Marks
    bIn a 33 kV overhead line, there are three units in the string of insulators. If the capacitance between each insulator pin and earth is 11% of self-capacitance of each insulator, Find :

    1. i)The distribution of voltage over 3 insulators
    2. ii)String efficiency
    How to answer

    • Ratio K = shunt capacitance / self capacitance = 0.11
    • Voltage distribution formula for 3 units
    • Calculation of voltages across each disc
    • String efficiency = total voltage / (n x voltage of top unit)
13. 5 Marks
    aWhat do you understand by grading of insulators? Explain.
    How to answer

    • Definition of grading of insulators
    • Need for uniform voltage distribution
    • Methods of grading
    • Explanation with example
14. 5 Marks
    bExplain:

    1. i)Radial System
    2. ii)Ring main system
    3. iii)Inter connected system
    How to answer

    • Radial system layout and features
    • Ring main system layout and features
    • Interconnected system layout and features
    • Comparison of reliability
15. 4 Marks
    cExplain about the improvement of string efficiency by grading of units and guard ring.
    How to answer

    • Concept of grading of units with different capacitances
    • Use of guard ring for equalizing potential
    • Improvement in string efficiency
    • Diagram of guard ring arrangement
16. 5 Marks
    aWhy the transmission lines 3 phase 3 wire circuits while distribution lines are $3\varphi$, 4 wire circuits?
    How to answer

    • Need of 3-wire for transmission - balanced load no neutral
    • Need of 4-wire for distribution - single phase loads need neutral
    • Role of neutral in unbalanced distribution
    • Cost and safety considerations
17. 5 Marks
    bA 50 km long transmission line supplies a load of 5 MVA at 0.8 p.f. lagging at 33 kV. The efficiency of transmission is 90%. Calculate the volume of aluminium conductor required for the line when (i) single phase, 2-wire system is used (ii) 3-phase, 3-wire system is used. The specific resistance of aluminium is $2.85 \times 10^{-8} \Omega$m.
    How to answer

    • Given 5 MVA, 33 kV, 0.8 p.f., 90% efficiency, 50 km
    • Formula for volume of conductor for 1-phase 2-wire vs 3-phase 3-wire
    • Use specific resistance $2.85\times10^{-8} \Omega m$
    • Comparison of copper volumes
18. 4 Marks
    cDraw the single line diagram showing the location of all substation equipment's?
    How to answer

    • Single line diagram symbols for substation equipment
    • Location of transformer, breaker, isolator, CT, PT
    • Bus-bar arrangement
    • Neat labelled diagram