EX-404 Power System-I - Jun 2022 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
   aExplain the Non-Conventional methods of Power generation.
   How to answer

   • Define non-conventional / renewable generation vs conventional
   • List types: solar, wind, biomass, geothermal, tidal, small hydro
   • Brief working principle of each
   • Merits, limitations and applications in power system
2. 7 Marks
   bA generating station has the following data: Installed Capacity$=300 \text{MW}$ ; Capacity factor $= 50\%$ ; Annual load factor $= 60\%$ ; Annual cost of fuel, oil etc $= \text{Rs. } 9 \times 10^{7}$ ; Capital cost $= \text{Rs. }10^{9}$; annual interest and depreciation $= 10\%$. Calculate

   1. i)the minimum reserve capacity of the station
   2. ii)the cost per KWh generated.
   How to answer

   • Compute average demand from capacity factor and installed capacity
   • Compute maximum demand from annual load factor
   • Reserve = installed - maximum demand
   • Compute annual energy generated and total annual cost to get Rs/kWh
3. 7 Marks
   aDerive the expression for Inductance of a single phase Two wire line.
   How to answer

   • Consider flux linkages of conductor A and B including internal flux
   • Use $L = \psi/I$ with $r' = 0.7788r$
   • Add loop inductance of both conductors
   • Final expression $L = (\mu_0/\pi)\ln(D/r')$ per loop length
4. 7 Marks
   bCalculate the Capacitance of a $100 \text{ km}$ long $3\text{-}\Phi, 50 \text{ Hz}$ overhead transmission line consisting of 3 conductors, each of diameter $2 \text{ cm}$ and spaced $2.5 \text{ m}$ at the corners of an equilateral triangle.
   How to answer

   • Calculate radius from diameter and spacing $D = 2.5$ m
   • Use $C_n = 2\pi\varepsilon_0 / \ln(D/r)$ per phase per metre
   • Multiply by line length 100 km for total capacitance
   • Obtain value in $\mu F$
5. 7 Marks
   aExplain the Skin effect in Transmission line conductors.
   How to answer

   • Define skin effect as non-uniform current distribution
   • Explain cause: internal flux linkages and inductive reactance
   • Discuss effects: increased effective resistance, reduced internal inductance
   • Factors affecting: frequency, diameter, material, stranding
6. 7 Marks
   bExplain the concept of GMR and GMD.
   How to answer

   • Define GMR as geometric mean of distances for inductance
   • Define GMD as geometric mean of spacing for inductance/capacitance
   • Give formulas for single and bundled conductors
   • Explain use in $L$ and $C$ calculations
7. 7 Marks
   aDefine regulation of a $3\text{-}\Phi$ short transmission system and develop an expression for approximate voltage regulation.
   How to answer

   • Define regulation as $(|V_s|-|V_r|)/|V_r|$ for short line
   • Draw phasor diagram of $V_s = V_r + IZ$
   • Derive approximate expression in terms of $R, X, \cos\phi$
   • Condition for zero/maximum regulation
8. 7 Marks
   bA balanced $3\text{-}\Phi$ load of $30 \text{ MW}$ is supplied at $132 \text{ KV}$, $50 \text{ Hz}$ and $0.85$ pf lagging by means of a transmission line. The series impedance of a single conductor is $(20+j52)$ ohms and the total phase-neutral admittance is $315 \times 10^{-6}$ siemens. Using Nominal T method, determine

   1. i)A,B,C and D Constants of the line
   2. ii)Sending end voltage.
   How to answer

   • Convert load to per-phase $V_r, I_r$ with pf angle
   • Form nominal-T ABCD constants with $Z, Y$
   • Compute $A,B,C,D$ values
   • Compute sending-end voltage $V_s = AV_r + BI_r$ magnitude and line value
9. 7 Marks
   aWhat is a Power Circle diagram of a transmission line? Explain how it can be constructed and what useful information can be obtained from it.
   How to answer

   • Define receiving and sending power circle diagrams
   • Steps for construction using ABCD constants
   • Show constant $P, Q$ circles with centre and radius
   • List uses: max power, regulation, VAR requirements
10. 7 Marks
    bExplain briefly about the methods of Voltage Control.
    How to answer

    • Need for voltage control in power system
    • Methods: excitation control, tap-changing transformers, auto-transformers
    • Methods: series/shunt capacitors, synchronous condensers, STATCOM
    • Brief merits of each method
11. 7 Marks
    aWhat are the various types of line supports? Discuss suitability of each wire with reference to system voltage and span.
    How to answer

    • List supports: wooden, steel, RCC, lattice steel towers
    • Discuss span, voltage range and mechanical strength
    • Suitability for LV, 33kV, 132kV and EHV lines
    • Cost and maintenance comparison
12. 7 Marks
    bDerive an expression for Sag due to weight of the conductor, when the supports are at the same level.
    How to answer

    • Consider conductor suspended between equal level supports
    • Use parabolic approximation of catenary
    • Equate moments to get tension and dip relation
    • Final sag $S = wL^2/8T$
13. 7 Marks
    aDefine String efficiency. Explain the methods of improving String efficiency.
    How to answer

    • Define string efficiency = voltage across string / n x voltage of lowest unit
    • Causes of unequal distribution: shunt capacitance
    • Methods: grading, guard ring, longer cross-arm
    • Formulae and improvement limits
14. 7 Marks
    bWrite short notes on different types of insulators used for overhead lines.
    How to answer

    • List types: pin, suspension, strain, shackle, post insulators
    • Construction and voltage application of each
    • Merits/demerits for overhead lines
    • Selection criteria
15. 7 Marks
    aExplain the Single bus bar system with Sectionalization and what are its merits and demerits.
    How to answer

    • Draw single bus with sectionalizing switch/breaker
    • Operation under normal and fault conditions
    • Merits: low cost, sectional continuity, maintenance
    • Demerits: outage on bus fault, limited flexibility
16. 7 Marks
    bMake a list of the main equipments in a Substation and explain each in brief.
    How to answer

    • List: transformer, circuit breaker, isolator, CT/PT, lightning arrester
    • List: bus-bar, relays, earthing, control equipment
    • Brief function of each in substation
    • Importance for protection and operation