100+ High Voltage Fundamentals MCQs with Answers

High Voltage Engineering is an important area of electrical engineering focused on generating, measuring, controlling, testing, and safely handling high electrical voltages. It plays a critical role in power generation, transmission, distribution, substations, transformers, cables, switchgear, insulation systems, and other high-voltage equipment. A sound understanding of the subject requires knowledge of both fundamental electrical principles and the behavior of insulating materials under different electrical and environmental stresses.

This collection of 100 High Voltage Engineering multiple-choice questions provides a structured way to review these concepts. The questions cover a broad range of topics, including high-voltage generation and measurement, breakdown mechanisms in gases, liquids, and solids, corona, partial discharge, insulation coordination, impulse testing, surge protection, cables, bushings, GIS, grounding, and high-voltage safety. Along with direct conceptual questions, the set also includes application-oriented and tricky questions designed to test understanding rather than simple memorization.

Each question is accompanied by the correct answer, a short hint, and an explanation. This format makes the collection useful for students preparing for university examinations, competitive examinations, technical interviews, and for professionals who want to refresh their knowledge of high-voltage engineering.

1). The dielectric strength of an insulating material is defined as?

Maximum current it can carry

Maximum electric field it can withstand without breakdown

Minimum voltage required for operation

Energy stored per unit volume

2).The SI unit of electric field intensity is?

Coulomb

Volt

Volt/meter

Ohm-meter

3). Which factor generally increases the electric field concentration near an electrode?

Increasing its radius of curvature

Making the electrode surface smoother and larger

Decreasing its radius of curvature

Increasing the electrode spacing only

4). In a uniform electric field, the electric field intensity is approximately:

Zero everywhere

Constant throughout the gap

Maximum only at the cathode

Maximum only at the anode

5). The term "clearance" in insulation design generally refers to?

Distance along an insulating surface

Distance through the insulating medium or air

Thickness of conductor

Length of an earth conductor

6). Creepage distance is measured?

Through the insulation bulk

Along the surface of insulation

Through the conductor

Between two earth electrodes

7). Which condition generally causes greater electrical stress at a conductor surface?

Large-radius smooth conductor

Small-radius sharp conductor

Perfectly spherical large conductor

Large smooth plate

8). If the voltage across a 10 mm air gap is 100 kV, the average electric field is approximately?

1 kV/mm

5 kV/mm

10 kV/mm

100 kV/mm

9). Why are rounded electrodes preferred in high-voltage equipment?

They increase resistance

They reduce electric-field concentration

They increase corona intentionally

They eliminate capacitance

10). Insulation coordination primarily involves?

Selecting conductor size only

Matching insulation strength with expected overvoltages and protective devices

Selecting transformer oil only

Increasing system frequency

11). Which equipment is commonly used to generate high AC voltages for testing?

Test transformer

Current transformer

Induction motor

Shunt reactor

12). The main purpose of using a cascade transformer arrangement is to?

Reduce voltage

Obtain very high AC voltages

Generate high current at low voltage

Improve power factor

13). In a Cockcroft-Walton voltage multiplier, capacitors are primarily used for?

Cooling

Energy storage and voltage multiplication

Current measurement

Magnetic shielding

14). A Marx generator is primarily used for generating?

Low-frequency AC

High-current DC

High-voltage impulse

Constant low voltage

15). During charging of a conventional Marx generator, its capacitors are connected approximately?

In series

In parallel

Directly to ground

In delta

16). The main purpose of a rectifier in a high-voltage DC generator is to:

Convert DC into AC

Convert AC into DC

Increase frequency

Reduce insulation strength

17). A standard lightning impulse voltage waveform is commonly represented as?

50/60 Hz

1.2/50 μs

10/100 ms

100/200 μs only

18). Switching impulse voltages are mainly associated with:

Battery charging

Switching operations in power systems

Household appliances

Transformer oil filtration

19). In an impulse voltage waveform, the "front time" primarily describes?

Time taken to reach the specified peak

Total duration of the test

Time to cool the generator

Time between two tests

20). A high-voltage DC generator is particularly useful when?

Only low-voltage AC is required

DC insulation or equipment needs testing

Frequency must be increased

Mechanical power must be generated

21). A sphere gap can be used for measuring?

Temperature

High voltage

Frequency only

Insulation resistance only

22). One major advantage of a sphere gap is that it provides:

A direct mechanical indication of voltage

A relatively simple method of measuring peak voltage

Continuous current measurement

Automatic insulation repair

23). A capacitive voltage divider is especially suitable for measuring?

Only temperature

AC and impulse voltages

Mechanical vibration

DC current only

24). The output of a resistive voltage divider is proportional to:

Input voltage

Input frequency only

Ambient temperature only

Electrode material only

25). An electrostatic voltmeter operates mainly based on:

Magnetic attraction

Electrostatic force

Thermal expansion

Chemical reaction

High Voltage Fundamentals MCQs for Exams

26). Which measuring arrangement is particularly important when measuring very fast impulse voltages?

Slow thermal meter

Properly designed voltage divider

Ordinary moving-coil meter

Incandescent lamp

27). Why is a high-voltage measuring divider usually connected to an oscilloscope or digital recorder?

To reduce atmospheric pressure

To observe the voltage waveform

To increase insulation thickness

To generate corona

28). Calibration of a high-voltage measuring system is necessary primarily to:

Increase its physical size

Establish measurement accuracy and traceability

Increase corona

Reduce conductor resistance

29). A capacitive divider may produce inaccurate results if?

Stray capacitances are ignored

The voltage is known

The electrodes are rounded

The measuring cable is properly compensated

30). The uncertainty in a high-voltage measurement can be affected by:

Divider ratio

Calibration

Environmental conditions

All of the above

31). Paschen's law relates breakdown voltage primarily to:

Temperature and current

Pressure and electrode separation

Frequency and resistance

Capacitance and inductance

32). An electron avalanche in a gas occurs when:

Electrons repeatedly cause ionizing collisions

Electrons stop moving

All ions become neutral

The gas becomes a perfect conductor instantly

33). Townsend's first ionization coefficient represents:

Ionization produced by electrons per unit distance

Current through an insulator

Heat produced by a conductor

Number of electrodes

34). The second Townsend ionization coefficient is associated mainly with?

Secondary electron emission from the cathode

Transformer cooling

Cable capacitance

Magnetic flux

35). Corona discharge is most likely to occur:

Only in a perfectly uniform field

Near regions of high electric-field concentration

Only inside solid insulation

Only at zero voltage

36). Which change generally reduces corona around a high-voltage conductor?

Decreasing conductor radius

Increasing conductor radius

Adding sharp edges

Increasing surface roughness

37). Corona on transmission lines can cause:

Radio interference

Audible noise

Power loss

All of the above

38). Which electrode arrangement tends to provide a more uniform electric field?

Point-to-plane

Sphere-to-plane

Parallel plates

Needle-to-needle

39). A negative point-to-plane corona is associated with:

Corona occurring around the high-field point electrode

No ionization

Complete absence of current

Breakdown of solid insulation only

40). Paschen's curve generally contains a minimum breakdown voltage at a particular:

A. Current value

Pressure-distance product

Temperature only

Electrode diameter only

41). Transformer oil is primarily used in transformers for:

Only mechanical lubrication

Insulation and heat transfer

Increasing frequency

Producing magnetic flux

42). Moisture contamination in transformer oil generally:

Increases dielectric strength

Reduces dielectric strength

Has no effect

Eliminates partial discharge

43). The breakdown voltage of insulating oil is commonly determined using:

A standard oil test cell

A tachometer

A watt-hour meter

A frequency counter only

44). Gas bubbles in liquid insulation are dangerous because:

They always have higher dielectric strength than liquid

They can create regions of enhanced electric stress

They reduce electric stress everywhere

They eliminate ionization

45). Filtering transformer oil primarily helps remove?

Dissolved magnetic flux

Solid contaminants and particles

Electrical voltage

Frequency components

46). Vacuum dehydration of transformer oil is mainly intended to remove?

Copper

Moisture

Nitrogen only

Magnetic flux

47). Dissolved Gas Analysis (DGA) of transformer oil is used mainly to:

Determine transformer color

Detect internal electrical and thermal faults

Measure transformer weight

Measure cable length

48). A high concentration of acetylene in transformer oil can be associated with:

Severe arcing

Normal cooling

Low humidity only

Mechanical lubrication

49). Which property is desirable in a liquid insulating material?

High electrical conductivity

High dielectric strength

High moisture content

High impurity concentration

50). One important reason for degassing insulating oil is to:

Increase the number of bubbles

Reduce gas-related discharge and breakdown risk

Increase conductivity

Increase moisture

High Voltage Fundamentals MCQs for Interviews

51). Which of the following is commonly used as a solid insulating material?

Epoxy resin

Copper

Aluminium

Silver

52). Electrical treeing refers to:

A mechanical crack in a conductor

Branch-like degradation channels in solid insulation

Cooling channels in transformers

A grounding arrangement

53). Thermal breakdown of a dielectric can occur when:

Heat generation exceeds heat dissipation

Temperature is always zero

Electric field is absent

The dielectric has no losses

54). Intrinsic breakdown of a solid dielectric is primarily associated with:

Very high electric fields

Mechanical vibration only

Atmospheric humidity only

Low voltage operation

55). A void inside solid insulation is undesirable because:

It always increases dielectric strength

It can initiate partial discharge

It eliminates electric stress

It acts as a perfect conductor

56). Surface tracking refers to:

A conducting path developing along an insulating surface

Current flowing only through copper

Magnetic flux movement

Mechanical movement of a cable

57). Cracks in solid insulation can be dangerous because they:

Improve field uniformity

Concentrate electric stress and permit discharge

Eliminate capacitance

Always increase mechanical strength

58). Thermal aging of solid insulation generally causes:

Permanent improvement of insulation

Gradual deterioration of insulation properties

Zero dielectric loss

Increased mechanical strength indefinitely

59). The dielectric constant of a material affects its:

Electrical field distribution and capacitance

Mechanical color only

Weight only

Melting point only

60). Which construction technique can reduce the risk of internal void-related partial discharge?

Deliberately introducing air pockets

Proper vacuum casting and impregnation

Increasing contamination

Leaving cracks untreated

61). Partial discharge is best described as:

A. Complete breakdown across the entire insulation

Localized electrical discharge that does not completely bridge the insulation

Mechanical failure of a conductor

Normal load current

62). Partial discharge inception voltage (PDIV) is:

Voltage at which PD first becomes detectable under specified conditions

Voltage at which the transformer explodes

Minimum supply frequency

Voltage at which the conductor melts

63). Partial discharge extinction voltage refers to:

The voltage at which all power is generated

The voltage below which PD ceases during a controlled voltage reduction

The highest operating voltage

The voltage used to charge a battery

64). PRPD patterns are commonly plotted against:

Phase angle and discharge magnitude

Temperature and pressure only

Resistance and inductance only

Cable length and diameter only

65). Which defect is a common source of internal partial discharge?

Void in solid insulation

Perfectly homogeneous insulation

Large rounded conductor

Clean oil without bubbles

66). Corona can be considered a form of:

Partial discharge

Mechanical discharge

Thermal expansion

Magnetic saturation

67). The major concern with persistent partial discharge is:

It improves insulation

It can progressively deteriorate insulation

It reduces electric stress everywhere

It increases mechanical strength

68). PD testing is particularly useful for:

Condition assessment of insulation

Measuring transformer weight

Measuring conductor diameter

Determining room temperature only

69). Electrical noise during a PD measurement can:

Improve accuracy

Mask actual PD signals

Increase insulation strength

Prevent all breakdowns

70). A significant decrease in PD inception voltage over time may indicate?

Possible insulation deterioration

Improved insulation

Lower conductor resistance only

Increased mechanical strength

71). The primary objective of insulation coordination is to:

Maximize equipment size

Select insulation levels appropriate to expected overvoltages

Eliminate all transformers

Increase system frequency

72). BIL in high-voltage equipment commonly stands for:

Basic Insulation Level

Basic Inductive Load

Breakdown Insulation Loss

Battery Isolation Limit

73). A surge arrester is normally connected?

In series with the load

Between the energized conductor and earth

Only across a resistor

Inside the neutral conductor only

74). Modern metal-oxide surge arresters commonly use:

Zinc oxide

Copper oxide only

Aluminium wire

Carbon steel

75). A surge arrester should generally be installed close to the equipment it protects because:

Lead inductance can increase the voltage reaching the equipment

It increases equipment temperature

It reduces the conductor diameter

It increases transformer oil viscosity

High Voltage Fundamentals MCQs for Quiz

76). The primary purpose of a shield wire on an overhead transmission line is to:

Carry normal load current

Intercept lightning strokes

Increase conductor resistance

Control frequency

77). A protective margin in insulation coordination is included mainly to:

Account for uncertainties and variations

Increase system losses intentionally

Reduce conductor size

Eliminate all switching operations

78). Grading rings on high-voltage insulators are primarily used to:

Increase mechanical vibration

Control electric-field distribution

Increase conductor resistance

Reduce system frequency

79). Lightning overvoltages are generally characterized by:

Very slow voltage variation over hours

Rapid transient voltage changes

Constant DC voltage

Zero frequency

80). The main function of a surge arrester during an overvoltage is to:

Increase the overvoltage

Limit the voltage by conducting surge current to earth

Disconnect every load permanently

Generate a switching impulse

81). A withstand test is performed primarily to determine whether insulation:

Can withstand a specified test voltage without unacceptable failure

Has the correct color

Has sufficient mechanical weight

Produces maximum corona

82). A power-frequency withstand test normally uses:

High-frequency RF voltage

AC at the specified power frequency

DC only

Microwave radiation

83). An impulse test is especially useful for evaluating insulation against:

Lightning and switching transients

Constant temperature

Mechanical vibration only

Normal DC operation only

84). Insulation resistance is commonly measured using a:

Megohmmeter

Tachometer

Ammeter only

Frequency meter only

85). The dielectric loss angle is associated with:

Energy loss in a dielectric

Mechanical vibration

Conductor diameter

Transformer turns ratio only

86). For an ideal lossless dielectric, the dissipation factor tan δ is:

Zero

One

Ten

Infinite

87). Very-low-frequency testing is commonly associated with:

Testing certain power cables

Measuring room temperature

Testing batteries only

Measuring magnetic flux

88). During a high-voltage withstand test, an unexpected insulation failure generally indicates:

The insulation successfully passed

Insulation breakdown occurred

Measurement is automatically correct

The test voltage was zero

89). Before conducting a high-voltage test, the test area should primarily be:

Open to everyone

Properly isolated, barricaded, and controlled

Filled with water

Connected to multiple unplanned sources

90). After a high-voltage DC test, the test object should be:

Immediately touched

Discharged and properly grounded

Left floating indefinitely

Connected to a higher voltage source

91). Step potential is the voltage difference between:

Two points on the ground separated by approximately one step

Phase and neutral only

Two transformer windings

Two battery terminals

92). Touch potential refers to the voltage between:

Two phase conductors

A grounded object and the point where a person stands

Two battery cells

Two turns of a transformer

93). The primary purpose of a substation grounding grid is to:

Increase fault voltage

Provide a low-impedance path for fault current and control ground potential gradients

Increase transformer losses

Increase system frequency

94). A cable bushing is primarily used to:

Allow a conductor to pass through a grounded enclosure while maintaining insulation

Increase cable resistance

Measure frequency

Generate lightning impulses

95). The metallic screen of a high-voltage cable can be used primarily to:

Control the electric field and provide a path for fault current

Increase corona intentionally

Increase insulation defects

Eliminate capacitance completely

96). Stress grading at a cable termination is used mainly to:

Concentrate electric field at one point

Reduce electric-field concentration near the termination

Increase mechanical noise

Eliminate conductor current

97). GIS stands for:

Gas-Insulated Switchgear

Grounded Internal System

General Insulation Standard

Gas-Induced Supply

98). One major advantage of GIS compared with conventional air-insulated switchgear is:

Much larger land requirement

Compact physical size

Complete absence of insulation

Higher exposure to environmental contamination

99). A major environmental concern associated with SF₆ is its:

Very high electrical conductivity

High global warming potential

Extremely low molecular weight

Ability to burn easily

100). The primary function of a high-voltage circuit breaker is to:

Increase fault current

Interrupt current under normal and/or fault conditions as designed

Increase system voltage permanently

Store electrical energy indefinitely

A strong understanding of High Voltage Engineering requires more than remembering definitions and standard terminology. Engineers must be able to recognize how electric fields, insulation characteristics, transient overvoltages, discharge phenomena, testing methods, and grounding practices interact in practical power systems. The 100 MCQs in this collection provide an opportunity to examine these concepts from different perspectives and identify areas that require further study.
The inclusion of hints and explanations is particularly useful for learning from incorrect answers. Instead of simply identifying the right option, learners can understand the principle behind it and relate the concept to actual high-voltage equipment and operating conditions. The tricky and application-oriented questions also encourage careful interpretation of the problem, which is essential when dealing with high-voltage systems where small design or operational errors can have serious consequences.
As high-voltage technology continues to evolve, particularly with developments in modern power networks, advanced insulation systems, renewable-energy integration, and compact switchgear, a strong foundation in these principles remains essential. Regular practice with questions such as these can help strengthen conceptual understanding and build the confidence needed to approach more advanced topics in High Voltage Engineering.