EX-702-C High Voltage Engineering - Jun 2025 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
   aDescribe the advantages of transmitting electrical power at high voltages.
   How to answer

   • Reduced current and I^2R losses for same power
   • Smaller conductor size, lower voltage drop and improved efficiency
   • Higher transmission capability and longer distances
   • Cost, insulation and corona trade-offs requiring HV technology
2. 7 Marks
   bExplain the HV technology, and mention the necessity of generating high DC voltage.
   How to answer

   • Meaning and scope of HV technology
   • Generation, transmission, testing and measurement aspects
   • Uses of high DC voltage in testing and HVDC
   • Necessity: insulation testing, research, HVDC transmission
3. 7 Marks
   aExplain the phenomenon of corona discharge and breakdown Mechanism in non-uniform fields.
   How to answer

   • Definition of corona and non-uniform field
   • Townsend/streamer processes leading to partial breakdown
   • Corona inception, visual and disruptive critical voltage
   • Transition from corona to complete breakdown
4. 7 Marks
   bExplain the breakdown mechanism of liquid dielectrics.
   How to answer

   • Nature of liquid dielectrics and impurities
   • Suspended particle, cavitation and stressed oil volume theories
   • Electronic and electro-convection breakdown
   • Factors: purity, temperature, pressure, electrode conditioning
5. 7 Marks
   aWhat do you understand by the intrinsic strength of solid dielectrics? Explain different mechanisms by which breakdown occurs in solid dielectrics in practice.
   How to answer

   • Definition of intrinsic strength as ideal material property
   • Electronic, thermal, electrochemical and tracking mechanisms
   • Practical breakdown: voids, surface, ageing effects
   • Comparison of intrinsic vs practical strength values
6. 7 Marks
   bExplain the cascaded connection of transformer for producing very high AC voltages.
   How to answer

   • Need for cascade to overcome single-unit voltage limit
   • Circuit arrangement with isolated tanks and series secondaries
   • Voltage distribution and balancing
   • Advantages and diagram of 2-3 stage cascade
7. 14 Marks
   Describe in brief :

   1. i)Tesla coil
   2. ii)Voltage doubler circuit
   3. iii)Generation of switching impulse voltage
   How to answer

   • Tesla coil: resonant high-frequency high voltage principle and circuit
   • Voltage doubler: Greinacher/Villard operation for DC doubling
   • Switching impulse generation: wave shape 250/2500 us and Marx/modified circuit
8. 7 Marks
   aWhat is the analysis of single stage impulse generator? Derive the expression for output impulse voltage.
   How to answer

   • Single-stage impulse generator circuit with charging and discharge elements
   • Laplace analysis of double-exponential wave
   • Derivation of $v(t)$ expression and front/tail time constants
   • Efficiency and wave-shape control
9. 7 Marks
   bExplain the Townsend's first and second ionization processes.
   How to answer

   • Townsend first coefficient alpha and electron avalanche
   • Second coefficient gamma: cathode secondary effects
   • Breakdown criterion $\gamma(e^{\alpha d}-1)=1$
   • Dependence on pressure, field and gas
10. 7 Marks
    aWith a neat sketch explain the Cockcroft - Walton voltage multiplier circuit for generation of high DC voltages.
    How to answer

    • Cockcroft-Walton multiplier ladder of capacitors and diodes
    • Charging operation on alternate half-cycles
    • Neat sketch with voltage build-up to n*Vm
    • Ripple, regulation and applications for high DC
11. 7 Marks
    bExplain the operation of electrostatic voltmeter with neat sketch.
    How to answer

    • Principle: electrostatic force proportional to V^2
    • Construction: fixed and moving electrodes, damping
    • Operation for AC/DC measurement
    • Neat sketch and use for high voltage
12. 7 Marks
    aDiscuss and compare the performance of resistance capacitance and mixed R-C potential dividers for measurement of impulse voltages.
    How to answer

    • Circuit of R, C and R-C damped dividers
    • Response to fast front: stray capacitance and inductance effects
    • Comparison of bandwidth, accuracy and loading
    • Choice for impulse voltage measurement
13. 7 Marks
    bDescribe the construction, principle of operation of a generating voltmeter and give its application and limitations.
    How to answer

    • Construction: rotating vaned rotor and stator electrodes
    • Principle: induced charge and commutated current proportional to V
    • Applications for HVDC and non-contact measurement
    • Limitations: speed stability, calibration, stray fields
14. 7 Marks
    aWrite short notes on the following.

    1. i)Testing of cable isolators
    2. ii)Testing of circuit breakers
    How to answer

    • Cable/isolator tests: power frequency, impulse and partial discharge
    • Circuit breaker tests: short-circuit, making/breaking, synthetic tests
    • Relevant standards and test circuits
    • Evaluation criteria
15. 7 Marks
    bDescribe in detail about Standard sphere gap measurements of HVAC and HVDC.
    How to answer

    • Sphere gap construction and standard diameters
    • Breakdown voltage vs gap distance tables for AC and DC
    • Procedure, corrections for temperature, humidity, polarity
    • Use as calibration and peak measurement