(SEM VII) THEORY EXAMINATION 2024-25 HIGH VOLTAGE ENGINEERING

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=I0​eαd

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.