KEE073 – HIGH VOLTAGE ENGINEERING
Complete Solved Question Paper
SECTION A
(Attempt all questions – 2 × 10 = 20 marks)
Q1(a) Paschen’s Law
Paschen’s Law states that the breakdown voltage in a gas depends on the product of gas pressure (p) and electrode gap distance (d).
Significance:
Helps in designing insulation systems and predicting breakdown voltage.
Q1(b) Townsend’s Criterion for Breakdown
Electrical breakdown occurs when:
γ(eαd−1)=1\gamma \left(e^{\alpha d} - 1\right) = 1γ(eαd−1)=1
where α is Townsend’s first ionization coefficient and γ is secondary ionization coefficient.
Q1(c) Generation of high DC voltages
High DC voltages are generated using: Rectifier circuits
Voltage multiplier circuits (Cockcroft–Walton) Electrostatic generators (Van de Graaff)
Q1(d) Principle of impulse generator
Impulse generator works on charging capacitors in parallel and discharging them in series to obtain high impulse voltage.
Q1(e) Measurement of high DC voltage
Resistance potential divider Electrostatic voltmeter
Sphere gap (indirect method)
Q1(f) Limitations of CRO
Limited voltage handling capacity Bandwidth limitation
Requires attenuation Sensitive to electromagnetic interference
Q1(g) Natural causes of overvoltages
Lightning strokes Switching operations
Insulation failure Ferro-resonance
Q1(h) Insulation coordination
Insulation coordination ensures proper selection of insulation levels so that equipment withstands overvoltages without failure.
Q1(i) Partial discharge
Partial discharge is a localized electrical discharge that does not completely bridge insulation.
Significance:
Indicates insulation degradation and aging.
Q1(j) Measurement of dielectric constant
Schering bridge Capacitance measurement method
Resonance method
SECTION B
(Attempt any three – 10 × 3 = 30 marks)
Q2(a) Townsend’s current growth equation
The current growth is given by: I=I0eαdI = I_0 e^{\alpha d}I=I0eαd
Significance:
Explains avalanche multiplication Basis of gaseous breakdown theory
Q2(b) Generation of high DC voltage
Methods:
Rectifier with smoothing filter Voltage multiplier circuits
Van de Graaff generator Used in HV testing laboratories.
Q2(c) Measurement techniques for high DC voltage
Potential divider Electrostatic voltmeter
Generating voltmeter Ensure accuracy and safety in measurement.
Q2(d) Lightning overvoltage & mitigation
Effects: Insulation failure
Equipment damage
Mitigation: Surge arresters
Shield wires Proper grounding
Q2(e) Measurement of dielectric constant & loss factor
Schering bridge Resonant circuits
Frequency variation methods Used for insulation assessment.
SECTION C
Q3(a) Streamer theory of breakdown
Initiated by ionization Formation of streamer channels
Rapid breakdown in gases Occurs at high electric fields and long gaps.
Q3(b) Breakdown in liquids
Pure liquids: Electronic breakdown
High dielectric strength
Commercial liquids: Impurity based breakdown
Bubble formation Lower strength
Q4(a) Generation of high AC voltages
Cascade transformers Resonant transformers
Tesla coil Used for AC insulation testing.
Q4(b) Impulse voltage generation
Generated using Marx impulse generator.
Factors affecting: Charging voltage
Capacitance Wave shaping resistors
Q5(a) Measurement of AC & impulse voltages
Sphere gap Potential divider
CRO with attenuators
Q5(b) CRO in HV measurement
Used to: Measure impulse shape
Record waveforms Measure rise time and peak value
Q6(a) Insulation coordination principles
Selection of insulation level Use of protective devices
Proper grounding Economic optimization
Q6(b) Effects of switching surges
Overvoltage stress Equipment damage
Insulation aging
Q7(a) Partial discharge measurement
Importance: Detect insulation defects
Predict failure Improve reliability
Methods include electrical and acoustic detection.
Q7(b) Transformer testing
Routine tests Type tests
Impulse tests Partial discharge tests
Ensures reliability and safety.
