High Voltage Engineering MCQs 2026

Townsend breakdown mechanism in gases describes

1. Aavalanche multiplication of electrons leading to ionization breakdown✓
2. Bonly liquid dielectric polarization✓
3. Conly solid lattice vibration✓
4. Donly magnetic saturation✓

Paschen law relates breakdown voltage in uniform field gaps to

1. Aonly temperature of conductor✓
2. Bonly humidity of oil alone✓
3. Conly cable length in km✓
4. Dproduct of pressure and gap distance (pd)✓

Streamer breakdown in long gaps at high pd is characterized by

1. Apurely uniform Townsend only at all gaps✓
2. Bno ionization whatsoever✓
3. Cbreakdown independent of electrode geometry✓
4. Dleader/streamer development bridging the gap rapidly✓

Dielectric breakdown in solids is often initiated by

1. Aperfect homogeneous lattice only always✓
2. Bzero electric field✓
3. Cimpurities, voids or thermal hot spots under high stress✓
4. Donly magnetic flux density✓

Liquid dielectric breakdown may involve

1. Aonly electron avalanche in vacuum always✓
2. Bbubble formation and electrohydrodynamic instability✓
3. Cno role of impurities✓
4. Dinfinite viscosity preventing motion✓

Impulse breakdown voltage of an insulator is typically

1. Aalways lower than DC breakdown✓
2. Bhigher than power-frequency breakdown for short duration stresses✓
3. Cequal to corona inception only✓
4. Dzero for lightning✓

Withstand voltage test on HV equipment verifies

1. Aonly contact resistance of terminals✓
2. Bonly nameplate MVA✓
3. Conly rotor inertia✓
4. Dinsulation can endure specified test voltage without failure✓

Creepage and clearance distances on insulators prevent

1. Aonly conductor heating✓
2. Bflashover along surfaces and through air✓
3. Conly skin effect✓
4. Donly transformer magnetizing current✓

Breakdown strength of air at atmospheric pressure in uniform field is approximately

1. A30 kV/cm order of magnitude✓
2. B1 V/cm✓
3. C1000 kV/cm always✓
4. Dindependent of gap✓

Vacuum breakdown at very small gaps can be worsened by

1. Aonly high humidity of air✓
2. Bonly oil viscosity✓
3. Conly cable capacitance✓
4. Dmicroparticles and field emission at electrode surfaces✓

Thermal breakdown in solid cable insulation occurs when

1. Adielectric losses cause heating exceeding heat removal capability✓
2. Bonly at zero voltage✓
3. Conly during DC corona✓
4. Donly in vacuum gaps✓

Electrode conditioning and humidity can

1. Anever affect results✓
2. Bfix Paschen minimum to zero✓
3. Csignificantly alter measured breakdown voltage in laboratory gaps✓
4. Deliminate need for standards✓

Corona discharge in HV systems is

1. Afull insulation puncture through solid dielectric✓
2. Bpartial ionization of air near conductors where local field exceeds ionization threshold✓
3. Conly DC motor commutation sparking✓
4. Donly transformer copper loss✓

Corona onset on a smooth conductor in air is related to

1. Asurface voltage gradient exceeding corona inception threshold✓
2. Bonly conductor length in km✓
3. Conly power factor of load✓
4. Donly frequency below 1 Hz only✓

Visual corona on HV lines is more noticeable

1. Aonly in dry desert at noon exclusively✓
2. Bonly inside oil-filled transformers visibly✓
3. Cduring wet or foggy conditions and at night✓
4. Donly at zero voltage✓

Corona power loss on transmission lines

1. Ais always zero on EHV lines✓
2. Bincreases with voltage above corona inception and with conductor surface conditions✓
3. Cdecreases as voltage rises without limit✓
4. Ddepends only on tower height✓

Bundled conductors on EHV lines reduce corona by

1. Aincreasing surface gradient✓
2. Bincreasing effective radius and lowering surface voltage gradient✓
3. Cremoving all electric field✓
4. Dusing only DC without any AC✓

Corona produces

1. Aonly useful heating of load✓
2. Bonly negative resistance in cables✓
3. Conly improved power factor always✓
4. Dozone, audible noise, light emission and power loss✓

Radio interference (RI) from corona on HV lines is mitigated by

1. Aincreasing sharp edges on conductors✓
2. Bremoving earth wire✓
3. Csmooth conductor surfaces, bundled conductors and optimized line design✓
4. Doperating at DC zero only✓

Positive and negative corona differ in that

1. Apositive corona is often more continuous while negative may be patchy (Trichel pulses)✓
2. Bthey are identical in all conditions✓
3. Conly negative exists in AC✓
4. Donly positive exists in vacuum✓

Corona ring (grading ring) on hardware reduces corona at

1. Atransformer core laminations only✓
2. Bconductor fittings, clamps and sharp edges✓
3. Cmotor rotor bars only✓
4. Dbattery terminals only✓

Fair weather corona loss estimation uses

1. Aonly transformer OC test data✓
2. Bonly cable Murray loop✓
3. Conly PID tuning constants✓
4. Dempirical formulas based on conductor size, voltage and weather✓

Under foul weather, corona and flashover risk

1. Adecreases to zero always✓
2. Bis unrelated to pollution✓
3. Cincreases due to water films and contamination on insulators✓
4. Deliminates need for creepage✓

DC corona on HVDC lines differs from AC because

1. ADC has no electric field✓
2. Bspace charge accumulates with one polarity affecting field distribution✓
3. CAC has no corona ever✓
4. DDC eliminates ionization✓

Corona inception voltage can be raised by

1. Apolishing conductor surface and increasing conductor diameter✓
2. Badding sharp points to conductors✓
3. Creducing clearance to ground✓
4. Dusing thinner single small conductor at same voltage✓

Insulation coordination ensures

1. Aequipment insulation levels are matched to expected overvoltages and protective devices✓
2. Bzero need for surge arresters✓
3. Cidentical BIL for all equipment regardless of role✓
4. Donly mechanical strength of towers✓

Basic Insulation Level (BIL) of equipment refers to

1. Acontinuous RMS voltage only✓
2. Bshort-circuit MVA only✓
3. Cspecified impulse withstand voltage capability✓
4. Dno-load current only✓

Metal-oxide surge arrester (MOA) protects equipment by

1. Aincreasing fault current intentionally✓
2. Bopening series breakers only✓
3. Cclamping overvoltages and diverting surge current to earth✓
4. Draising BIL of transformers permanently✓

Protective margin in insulation coordination is

1. Aalways zero by definition✓
2. Bdifference between equipment withstand and protective level of arrester✓
3. Cequal to line length only✓
4. Dsame as power factor✓

Switching surge is significant for insulation coordination on

1. Aonly 11 kV distribution✓
2. BEHV and UHV systems above about 300 kV✓
3. Conly DC control circuits✓
4. Donly motor starter panels✓

CFO (critical flashover) voltage of an insulator string is used in

1. Astatistical insulation coordination studies✓
2. Bonly DC resistance measurement✓
3. Conly motor slip calculation✓
4. Donly cable ampacity tables✓

Temporary overvoltage (TOV) following fault or load rejection can

1. Astress arrester and insulation if not coordinated✓
2. Bnever occur on transmission lines✓
3. Conly affect LV fuses✓
4. Deliminate Ferranti rise✓

Shielding angle and earth wire design on transmission lines improve

1. Aonly corona loss without shielding effect✓
2. Bonly cable charging current✓
3. Clightning protection by reducing strikes to phase conductors✓
4. Donly transformer impedance✓

Standard lightning impulse test wave shape is commonly

1. ADC ramp only✓
2. B50 Hz sine only✓
3. Csquare wave of 1 ms only✓
4. D1.2/50 μs voltage wave✓

Pollution level of an installation site affects

1. Arequired creepage distance of outdoor insulators✓
2. Bonly conductor ampacity✓
3. Conly rotor resistance✓
4. Donly battery capacity✓

Coordination between arrester rating and transformer insulation considers

1. Amaximum continuous operating voltage and temporary overvoltages✓
2. Bonly no-load loss✓
3. Conly motor starting current✓
4. Donly cable burial depth✓

Silhouette factor and specific creepage distance (SCD) are used to select

1. Aonly underground cable size✓
2. Binsulator profiles for polluted environments✓
3. Conly VFD carrier frequency✓
4. Donly train pantograph pressure✓

High-voltage AC test transformers are used to

1. Aonly measure earth resistance✓
2. Bonly start induction motors✓
3. Cproduce test voltages for dielectric withstand and partial discharge tests✓
4. Donly regulate turbine governors✓

Partial discharge (PD) measurement detects

1. Aonly copper losses in windings✓
2. Bonly rotor speed deviation✓
3. Clocalized dielectric stress that may precede insulation failure✓
4. Donly solar irradiance✓

Tan delta (dielectric loss angle) test on insulation indicates

1. Aonly conductor cross-section✓
2. Bdielectric quality and moisture or ageing✓
3. Conly gearbox ratio✓
4. Donly wind cut-in speed✓

Impulse generator Marx circuit produces

1. Aonly DC ripple free voltage✓
2. Bhigh lightning or switching impulse voltages for testing✓
3. Conly 50 Hz unregulated supply✓
4. Donly biogas pressure✓

Sphere gap is used in HV laboratories to

1. Ameasure only current transformer ratio✓
2. Bcalibrate only watt-hour meters✓
3. Cmeasure peak voltage by calibrated breakdown spacing✓
4. Dtest only soil pH✓

SF6 gas in HV switchgear and GIS provides

1. Alower dielectric strength than air at same pressure✓
2. Bonly lubrication of contacts✓
3. Conly cooling of solar panels✓
4. Dhigh dielectric strength and arc quenching capability✓

Vacuum interrupter in HV breakers extinguishes arc by

1. Aoil blast only✓
2. Bair at atmospheric pressure only✓
3. Cwater jet only✓
4. Drapid reduction of plasma in high vacuum with metal vapour condensation✓

Capacitance voltage divider (CVD) is used for

1. Ameasuring high voltages by ratio of capacitors✓
2. Bstarting synchronous motors only✓
3. Cbiogas methane measurement only✓
4. Dyaw control of wind turbines only✓

Field intensity on an HV bushing is controlled by

1. Asingle uniform paper layer only✓
2. Bremoving all capacitive grading✓
3. Cusing only air gaps internally✓
4. Dgraded insulation and condenser layers✓

Routine tests on HV transformers include

1. Aonly blade pitch angle✓
2. Bonly train braking distance✓
3. Cmeasurement of ratio, polarity, winding resistance and insulation resistance✓
4. Donly MPPT algorithm code✓

Type tests on HV equipment demonstrate

1. Aonly paint colour compliance✓
2. Bonly nameplate font size✓
3. Conly shipping weight✓
4. Ddesign meets standard requirements including dielectric and thermal limits✓

Earthing of HV test areas and labs is critical to

1. Aincrease corona on purpose✓
2. Beliminate all insulation✓
3. Cmeasure only solar Voc✓
4. Dpersonnel safety and correct fault current paths during tests✓