Q.1 What is dielectric breakdown?
A sudden increase in resistance of a material
A sudden decrease in resistance of a material
The permanent removal of electrons from a material
The permanent addition of electrons to a material
Explanation - Dielectric breakdown occurs when a material suddenly becomes conductive, allowing a large current to flow through it.
Correct answer is: A sudden decrease in resistance of a material
Q.2 Which of the following is NOT a factor that influences dielectric breakdown voltage?
Material purity
Temperature
Ambient pressure
Color of the material
Explanation - Dielectric breakdown depends on material properties, temperature, and pressure, but the color of the material is not relevant.
Correct answer is: Color of the material
Q.3 What is Paschen's law used for?
Calculating the magnetic field of a conductor
Predicting the breakdown voltage in gases
Determining the resistivity of metals
Estimating the capacitance of a capacitor
Explanation - Paschen's law provides a relationship between the breakdown voltage, pressure, and distance between electrodes in a gas.
Correct answer is: Predicting the breakdown voltage in gases
Q.4 The dielectric strength of a material is measured in:
Volts per meter (V/m)
Amperes per second (A/s)
Ohms (Ω)
Joules (J)
Explanation - Dielectric strength indicates how much electric field a material can withstand, expressed in volts per meter.
Correct answer is: Volts per meter (V/m)
Q.5 Which material typically has the highest dielectric strength?
Air
Vacuum
Glass
Water
Explanation - Vacuum has the highest dielectric strength (~3 MV/m) because it has no particles to initiate breakdown.
Correct answer is: Vacuum
Q.6 A corona discharge is:
A complete breakdown of a material
A localized ionization around a high‑field point
A permanent increase in dielectric strength
An insulating phenomenon in high‑pressure gas
Explanation - Corona discharge is a localized ionization that occurs around sharp points when the field exceeds a threshold but is below full breakdown.
Correct answer is: A localized ionization around a high‑field point
Q.7 Which of the following is a common method to improve dielectric strength in composites?
Increasing porosity
Adding conductive fillers
Adding insulating fillers
Decreasing the material’s density
Explanation - Adding insulating fillers can reduce defects and improve the breakdown strength of composites.
Correct answer is: Adding insulating fillers
Q.8 The breakdown voltage of a gas increases with:
Temperature
Pressure
Humidity
Conductivity
Explanation - Paschen's law shows that, for most gases, breakdown voltage increases with pressure up to a point.
Correct answer is: Pressure
Q.9 Which phenomenon explains why water has lower dielectric strength than dry air?
Higher conductivity
Presence of ions
Higher density
Larger molecular size
Explanation - Water contains ions that facilitate ionization, lowering its dielectric strength.
Correct answer is: Presence of ions
Q.10 The dielectric constant of a material is:
A measure of its magnetic permeability
A measure of its electrical conductivity
A measure of its ability to store electric energy
A measure of its thermal conductivity
Explanation - The dielectric constant indicates how much electric field energy a material can store per unit volume.
Correct answer is: A measure of its ability to store electric energy
Q.11 Which of the following best describes an insulator’s failure mode during dielectric breakdown?
It becomes a perfect conductor
It emits light without heat
Its resistance increases
It turns into a superconductor
Explanation - During breakdown, an insulator conducts current like a conductor, leading to a short circuit.
Correct answer is: It becomes a perfect conductor
Q.12 What role does humidity play in the dielectric strength of air?
Increases dielectric strength
Decreases dielectric strength
Has no effect
Creates a magnetic field
Explanation - Higher humidity reduces air’s dielectric strength because water vapor increases ionization probability.
Correct answer is: Decreases dielectric strength
Q.13 Which of the following is a typical application of high‑voltage dielectric testing?
Determining the tensile strength of steel
Measuring the capacitance of a capacitor
Testing the insulation quality of power cables
Testing the chemical composition of alloys
Explanation - High‑voltage dielectric testing ensures that insulation can withstand operating voltages.
Correct answer is: Testing the insulation quality of power cables
Q.14 What is the main advantage of using silicone oil for insulation?
High dielectric strength
Low cost
Easy to evaporate
High conductivity
Explanation - Silicone oil offers a high dielectric strength and excellent cooling properties.
Correct answer is: High dielectric strength
Q.15 When a dielectric material breaks down, what is the typical time scale of the discharge?
Seconds
Milliseconds
Nanoseconds
Years
Explanation - Dielectric breakdown is a very fast event, typically occurring on the nanosecond scale.
Correct answer is: Nanoseconds
Q.16 Which gas has the lowest breakdown voltage in air?
Oxygen
Nitrogen
Argon
Hydrogen
Explanation - Hydrogen has a relatively low breakdown voltage compared to other common gases.
Correct answer is: Hydrogen
Q.17 Which of these is a common test for dielectric strength?
Pull test
Tensile test
Dielectric withstand test
Hardness test
Explanation - The dielectric withstand test applies increasing voltage until breakdown occurs.
Correct answer is: Dielectric withstand test
Q.18 Which of the following phenomena is NOT related to dielectric breakdown?
Corona discharge
Sparking
Thermal conduction
Arc formation
Explanation - Dielectric breakdown is related to electrical phenomena, not thermal conduction directly.
Correct answer is: Thermal conduction
Q.19 What is the typical dielectric strength of a standard air gap at sea level?
3 kV/mm
30 kV/mm
300 kV/mm
3000 kV/mm
Explanation - Air has a dielectric strength of about 30 kV/mm at standard conditions.
Correct answer is: 30 kV/mm
Q.20 Which of the following is a direct consequence of dielectric breakdown?
Increased resistance
Formation of a conductive path
Cooling of the material
Increase in dielectric constant
Explanation - Dielectric breakdown creates a path for current, effectively turning the insulator into a conductor.
Correct answer is: Formation of a conductive path
Q.21 Which property of a material is most critical in predicting its dielectric strength?
Melting point
Band gap
Molecular weight
Color
Explanation - A larger band gap generally correlates with higher dielectric strength.
Correct answer is: Band gap
Q.22 How does temperature affect dielectric strength of polymers?
It always increases
It always decreases
It has no effect
It depends on the polymer
Explanation - Some polymers are temperature stable while others lose strength when heated.
Correct answer is: It depends on the polymer
Q.23 What is the typical unit used to express the dielectric strength of liquids?
V/m
kV/mm
Pa
W/m²
Explanation - Dielectric strength of liquids is normally given in volts per meter.
Correct answer is: V/m
Q.24 Which of the following materials is NOT commonly used as insulation in high‑voltage equipment?
Bakelite
Polyethylene
Copper
Glass
Explanation - Copper is a conductor, not an insulator.
Correct answer is: Copper
Q.25 What effect does increasing the electrode spacing have on the breakdown voltage in a gas?
Decreases the voltage
Increases the voltage
No effect
Causes immediate breakdown
Explanation - A larger gap requires a higher voltage to achieve the same electric field for breakdown.
Correct answer is: Increases the voltage
Q.26 Which of the following best explains why a corona discharge emits light?
Electron recombination
Molecular vibration
Chemical reaction
Magnetic field generation
Explanation - The excited electrons recombine with ions, emitting photons that produce visible light.
Correct answer is: Electron recombination
Q.27 What is the main reason for using a gas like SF₆ in high‑voltage switchgear?
It is inexpensive
It has high dielectric strength
It is a good conductor
It is a liquid at room temperature
Explanation - SF₆ provides excellent insulation and arc extinguishing properties.
Correct answer is: It has high dielectric strength
Q.28 Which test is performed to determine the time‑to‑failure of insulation under a constant voltage?
Short‑time withstand test
Time‑of‑life test
Partial discharge test
Thermal aging test
Explanation - The time‑of‑life test measures how long insulation can survive a sustained voltage.
Correct answer is: Time‑of‑life test
Q.29 Which of the following best describes the role of an electric field in dielectric breakdown?
It reduces resistance
It creates electron avalanches
It increases the material’s temperature
It prevents ionization
Explanation - A strong electric field accelerates electrons, leading to avalanches that cause breakdown.
Correct answer is: It creates electron avalanches
Q.30 In a composite dielectric, why is a low porosity desirable?
It increases weight
It reduces dielectric strength
It prevents void‑induced breakdown
It lowers the dielectric constant
Explanation - Voids act as local high‑field regions; low porosity reduces this risk.
Correct answer is: It prevents void‑induced breakdown
Q.31 Which of these is NOT a typical symptom of impending dielectric breakdown?
Partial discharges
Corona noise
Sudden heat spike
Gradual increase in resistance
Explanation - Breakdown usually shows a decrease, not an increase, in resistance.
Correct answer is: Gradual increase in resistance
Q.32 Which of the following is a key difference between AC and DC breakdown voltages?
AC breakdown is always higher
DC breakdown is always higher
They are always equal
AC breakdown depends on frequency
Explanation - DC requires a higher voltage to initiate breakdown because the field is steady.
Correct answer is: DC breakdown is always higher
Q.33 What is the typical dielectric strength of transformer oil?
50 kV/mm
30 kV/mm
10 kV/mm
5 kV/mm
Explanation - Transformer oil normally has a dielectric strength around 30 kV/mm.
Correct answer is: 30 kV/mm
Q.34 Which material has the lowest dielectric strength among the following?
Polypropylene
Polystyrene
Polytetrafluoroethylene (PTFE)
Teflon
Explanation - Polystyrene has a lower dielectric strength (~30 kV/mm) compared to PTFE.
Correct answer is: Polystyrene
Q.35 Which of the following is a primary cause of dielectric breakdown in high‑temperature environments?
Increased humidity
Thermal expansion
Mechanical stress
Chemical reactions
Explanation - Heat can cause expansion and micro‑cracks, lowering dielectric strength.
Correct answer is: Thermal expansion
Q.36 Which parameter is NOT part of Paschen's equation?
Pressure (p)
Gap distance (d)
Temperature (T)
Voltage (V)
Explanation - Paschen's equation includes pressure, gap distance, and voltage, but not temperature.
Correct answer is: Temperature (T)
Q.37 Which of the following is a safety measure to prevent accidental dielectric breakdown?
Increase voltage gradually
Use high‑conductivity wires
Add metal shunts across the gap
Ignore partial discharges
Explanation - Gradual voltage ramping allows for early detection of partial discharges.
Correct answer is: Increase voltage gradually
Q.38 What is the primary effect of adding a small amount of conductive filler to a dielectric?
Increases dielectric strength
Decreases dielectric strength
No effect
Makes the material magnetic
Explanation - Conductive fillers provide pathways for current, lowering the breakdown threshold.
Correct answer is: Decreases dielectric strength
Q.39 Which of these is a characteristic of a material that resists corona discharge?
Sharp edges
Smooth surfaces
High electrical conductivity
Large grain size
Explanation - Smooth surfaces reduce high‑field concentration that can lead to corona.
Correct answer is: Smooth surfaces
Q.40 Why does a vacuum have the highest dielectric strength?
No ionizable particles
High conductivity
Large atomic size
Low pressure only
Explanation - In a vacuum there are no particles to ionize, requiring the highest voltage for breakdown.
Correct answer is: No ionizable particles
Q.41 Which of the following best describes a 'partial discharge'?
A complete breakdown of a material
A localized discharge that does not bridge the entire dielectric
A high‑temperature event in conductors
A magnetic field anomaly
Explanation - Partial discharges occur within voids or defects but do not fully short the material.
Correct answer is: A localized discharge that does not bridge the entire dielectric
Q.42 Which of these is a common symptom of dielectric ageing?
Increase in capacitance
Decrease in dielectric loss
Improved conductivity
Decreased dielectric strength
Explanation - Ageing typically reduces the material’s ability to withstand high electric fields.
Correct answer is: Decreased dielectric strength
Q.43 What is the effect of a high electric field on a polymer chain?
It strengthens the chain
It causes chain scission
It makes the polymer superconductive
It turns the polymer into a metal
Explanation - High electric fields can break polymer chains, leading to breakdown.
Correct answer is: It causes chain scission
Q.44 Which of these is NOT a typical method to measure partial discharges?
Ultrasonic sensors
Current probes
Temperature sensors
Electrostatic sensors
Explanation - Partial discharges are measured by acoustic or electrical sensors, not directly by temperature.
Correct answer is: Temperature sensors
Q.45 Which parameter is most directly proportional to dielectric strength in solid dielectrics?
Temperature
Band gap
Conductivity
Thickness
Explanation - A larger band gap usually means the material can withstand higher fields before breakdown.
Correct answer is: Band gap
Q.46 The term 'spark gap' refers to:
A device that generates high voltage
A small air gap used as a switch
A type of corona discharge
A measurement of dielectric constant
Explanation - A spark gap is an air gap that conducts when the field exceeds the breakdown threshold.
Correct answer is: A small air gap used as a switch
Q.47 Which of the following is true about dielectric breakdown in liquids?
It occurs instantaneously at low voltages
It is unaffected by temperature
It typically forms a visible spark
It is a purely mechanical phenomenon
Explanation - Breakdown in liquids often manifests as a visible spark due to ionization.
Correct answer is: It typically forms a visible spark
Q.48 What is the typical dielectric strength of a high‑purity PTFE material?
40 kV/mm
30 kV/mm
20 kV/mm
10 kV/mm
Explanation - PTFE has a dielectric strength around 40 kV/mm in high‑purity form.
Correct answer is: 40 kV/mm
Q.49 Which of the following best describes the 'electrostrictive' effect?
A change in shape due to temperature
A change in shape due to magnetic field
A change in shape due to electric field
A change in shape due to pressure
Explanation - Electrostriction is the mechanical deformation of a dielectric under an electric field.
Correct answer is: A change in shape due to electric field
Q.50 Which of these gases is known for its excellent arc quenching properties?
Air
Nitrogen
SF₆
Helium
Explanation - SF₆ is widely used in high‑voltage switchgear for its arc suppression capability.
Correct answer is: SF₆
Q.51 Which of these is a likely cause of dielectric breakdown in a solid insulating material?
High humidity
Mechanical vibration
Presence of voids
Low temperature
Explanation - Voids can concentrate the electric field, promoting breakdown.
Correct answer is: Presence of voids
Q.52 What does the term 'dielectric loss tangent' describe?
The ratio of stored to dissipated energy
The maximum voltage a dielectric can withstand
The physical thickness of a dielectric
The frequency at which breakdown occurs
Explanation - The loss tangent indicates how much energy is lost as heat in the dielectric.
Correct answer is: The ratio of stored to dissipated energy
Q.53 Which of the following is NOT a typical high‑voltage test for insulation integrity?
High‑voltage withstand test
Partial discharge test
Thermogravimetric analysis
Dielectric loss measurement
Explanation - Thermogravimetric analysis measures mass change with temperature, not electrical integrity.
Correct answer is: Thermogravimetric analysis
Q.54 A material with high dielectric strength is often used as:
Conductor
Insulator
Magnet
Resistor
Explanation - High dielectric strength indicates resistance to electric breakdown, a key property for insulators.
Correct answer is: Insulator
Q.55 Which of these is a major risk when a high‑voltage device experiences dielectric breakdown?
Increased mechanical strength
Overheating and fire
Lower operating voltage
Improved insulation
Explanation - Breakdown creates a short circuit that can cause overheating and potentially ignite a fire.
Correct answer is: Overheating and fire
Q.56 What does a 'voltage gradient' refer to in the context of dielectric breakdown?
Voltage difference per unit distance
Rate of voltage change over time
Difference in voltage across a resistor
Difference in voltage between two points in a circuit
Explanation - Voltage gradient is the electric field strength, which is crucial in breakdown analysis.
Correct answer is: Voltage difference per unit distance
Q.57 Which of the following materials typically exhibits the lowest dielectric loss at high frequencies?
Glass
Polyethylene
Polyvinyl chloride (PVC)
Polypropylene
Explanation - Polypropylene has a very low dielectric loss at high frequencies, making it ideal for high‑frequency applications.
Correct answer is: Polypropylene
Q.58 Which phenomenon is responsible for the sudden flashover in a high‑voltage switchgear?
Corona discharge
Arcing
Thermal expansion
Magnetic induction
Explanation - Arcing occurs when the electric field exceeds the breakdown strength, forming a conductive path.
Correct answer is: Arcing
Q.59 In a dielectric material, what does a high 'relative permittivity' imply?
It stores more electric energy
It conducts electricity easily
It has a low breakdown voltage
It is magnetic
Explanation - Relative permittivity (dielectric constant) indicates how much energy a material can store.
Correct answer is: It stores more electric energy
Q.60 Which of the following is a typical sign of a developing dielectric breakdown in a transformer?
Increasing oil viscosity
Decreasing core temperature
Increasing partial discharge count
Improving insulation resistance
Explanation - Higher partial discharge activity often signals insulation degradation.
Correct answer is: Increasing partial discharge count
Q.61 Which of these factors does NOT influence the dielectric breakdown of a vacuum gap?
Electric field strength
Electrode geometry
Ambient temperature
Presence of dust particles
Explanation - In a perfect vacuum, temperature has minimal effect on breakdown; field strength, geometry, and dust matter more.
Correct answer is: Ambient temperature
Q.62 Which of the following best explains why adding a small amount of conductive filler reduces dielectric strength?
It creates a stronger electric field
It introduces more defect sites
It increases the band gap
It reduces the material’s density
Explanation - Conductive fillers provide pathways for charge flow, facilitating breakdown.
Correct answer is: It introduces more defect sites
Q.63 In high‑voltage engineering, which test is performed at the operating voltage of equipment?
Short‑time withstand test
Time‑of‑life test
Partial discharge test
Dielectric loss measurement
Explanation - The time‑of‑life test applies the actual operating voltage to assess longevity.
Correct answer is: Time‑of‑life test
Q.64 Which of these is a common characteristic of an ideal dielectric?
Infinite electrical conductivity
Zero dielectric constant
Zero dielectric loss
Infinite dielectric strength
Explanation - An ideal dielectric would store energy without loss.
Correct answer is: Zero dielectric loss
Q.65 What is the main purpose of using a corona shield in high‑voltage equipment?
To increase voltage
To reduce ionization at sharp points
To decrease insulation thickness
To enhance magnetic fields
Explanation - Corona shields smooth out sharp edges, preventing localized ionization.
Correct answer is: To reduce ionization at sharp points
Q.66 Which of the following is the most likely cause of dielectric failure in an oil‑filled transformer?
Overheating
Insufficient voltage
Low humidity
High mechanical vibration
Explanation - Excess heat accelerates aging and reduces the dielectric strength of transformer oil.
Correct answer is: Overheating
Q.67 What does the 'breakdown field' of a material represent?
Maximum electric field it can withstand
Minimum electric field required for conduction
Electric field at which it becomes superconductive
Field that induces magnetic flux
Explanation - The breakdown field is the threshold electric field at which the material fails.
Correct answer is: Maximum electric field it can withstand
Q.68 Which of the following materials is commonly used as insulation in high‑voltage cables?
Copper
Aluminum
Polyethylene
Steel
Explanation - Polyethylene is widely used due to its good insulation properties and low cost.
Correct answer is: Polyethylene
Q.69 Which of these is a major contributor to the breakdown voltage of a gas?
Atomic weight of the gas
Ionization energy of the gas molecules
Color of the gas
Magnetic susceptibility
Explanation - Higher ionization energy requires more electric field to create free carriers.
Correct answer is: Ionization energy of the gas molecules
Q.70 Why is it important to maintain a clean surface on high‑voltage electrodes?
To increase the surface area
To reduce the local electric field
To prevent corrosion only
To increase mechanical strength
Explanation - Contaminants can create high‑field spots leading to breakdown.
Correct answer is: To reduce the local electric field
Q.71 Which of the following is a typical consequence of dielectric ageing?
Improved thermal conductivity
Reduced dielectric loss
Increased dielectric strength
Formation of micro‑cracks
Explanation - Ageing often leads to micro‑cracks that lower the breakdown threshold.
Correct answer is: Formation of micro‑cracks
Q.72 In a high‑voltage test, what is the primary purpose of a 'surge arrester'?
To increase the voltage rating
To protect against lightning surges
To reduce current in normal operation
To increase capacitance
Explanation - Surge arresters clamp the voltage during surges to prevent dielectric breakdown.
Correct answer is: To protect against lightning surges
Q.73 Which of the following is NOT a typical property measured during a dielectric analysis?
Dielectric strength
Permittivity
Conductivity
Magnetic permeability
Explanation - Dielectric analysis focuses on electric properties, not magnetic.
Correct answer is: Magnetic permeability
Q.74 Which of these gases is known for its high dielectric strength and is used as a coolant in high‑voltage equipment?
SF₆
CO₂
O₂
N₂
Explanation - SF₆ offers high dielectric strength and is commonly used in switchgear.
Correct answer is: SF₆
Q.75 What effect does an increase in electrode spacing have on the dielectric strength of a gas?
It decreases the dielectric strength
It increases the dielectric strength
It has no effect
It causes immediate breakdown
Explanation - A larger gap requires a higher voltage to reach the same electric field.
Correct answer is: It increases the dielectric strength
Q.76 Which of these is a typical cause of partial discharge in high‑voltage equipment?
Uniform material distribution
Presence of voids or defects
High purity of insulating material
Low operating temperatures
Explanation - Voids act as local high‑field zones where partial discharge can occur.
Correct answer is: Presence of voids or defects
Q.77 Which of these factors is most important for ensuring a high dielectric strength in a polymer?
Molecular weight
Purity
Color
Density
Explanation - Impurities can lower the dielectric strength by creating paths for ionization.
Correct answer is: Purity
Q.78 The 'critical electric field' is a term used to describe:
The field at which a material starts to conduct
The field at which a material becomes magnetic
The field at which a material melts
The field at which a material expands
Explanation - The critical electric field is the threshold for breakdown.
Correct answer is: The field at which a material starts to conduct
Q.79 Which of these is a typical method for detecting early dielectric breakdown?
Visual inspection
Thermal imaging
Partial discharge monitoring
Mechanical testing
Explanation - Partial discharge monitoring is used to detect early signs of breakdown.
Correct answer is: Partial discharge monitoring
Q.80 What is the primary factor that limits the dielectric strength of water?
High temperature
Presence of ions
High density
Low purity
Explanation - Ions lower the breakdown threshold of water.
Correct answer is: Presence of ions
Q.81 Which of the following is true about the dielectric constant of vacuum?
It is 0
It is 1
It is 10
It is 1000
Explanation - The dielectric constant of vacuum is defined as 1.
Correct answer is: It is 1
Q.82 Which of the following is a typical consequence of dielectric breakdown in a gas?
Increased insulation resistance
Decreased ionization
Formation of an arc
Reduction in temperature
Explanation - Breakdown in a gas often creates an arc that conducts current.
Correct answer is: Formation of an arc
Q.83 Which of these best describes the 'arc' in high‑voltage engineering?
A sudden increase in resistance
A sudden decrease in voltage
A short‑circuit current path
A magnetic field phenomenon
Explanation - An arc is a conductive path that forms when breakdown occurs.
Correct answer is: A short‑circuit current path
Q.84 Which of the following is an advantage of using silicone oil in high‑voltage insulation?
Low dielectric strength
High thermal conductivity
High dielectric strength and good cooling
High electrical conductivity
Explanation - Silicone oil provides excellent insulation and cooling properties.
Correct answer is: High dielectric strength and good cooling
Q.85 In a solid dielectric, what is typically the main mechanism of breakdown?
Magnetic field penetration
Thermal conduction
Electron avalanche
Mechanical failure
Explanation - High fields accelerate electrons, creating avalanches that lead to breakdown.
Correct answer is: Electron avalanche
Q.86 Which of these is a key parameter in Paschen's law for gas breakdown?
Gas composition
Electrode geometry
Pressure × Distance
Temperature
Explanation - Paschen's law relates breakdown voltage to the product of pressure and gap distance.
Correct answer is: Pressure × Distance
Q.87 Which of the following materials has the highest dielectric strength among common polymers?
Polyethylene
Polypropylene
Polyvinyl chloride (PVC)
Polytetrafluoroethylene (PTFE)
Explanation - PTFE can withstand the highest electric fields among common polymers.
Correct answer is: Polytetrafluoroethylene (PTFE)
Q.88 Which of these is a typical effect of high humidity on air dielectric strength?
Increase in dielectric strength
Decrease in dielectric strength
No change
Complete loss of dielectric constant
Explanation - Higher humidity lowers air’s dielectric strength.
Correct answer is: Decrease in dielectric strength
Q.89 What is the main purpose of a 'breakdown voltage' test?
To measure electrical conductivity
To determine the maximum voltage a material can withstand
To evaluate thermal conductivity
To assess magnetic permeability
Explanation - Breakdown voltage tests find the voltage at which a material fails electrically.
Correct answer is: To determine the maximum voltage a material can withstand
Q.90 Which of the following best describes an 'insulation defect'?
A region with higher dielectric constant
A void or micro‑crack causing local field enhancement
A uniform material without any voids
A region with zero conductivity
Explanation - Insulation defects act as hot spots for breakdown initiation.
Correct answer is: A void or micro‑crack causing local field enhancement
Q.91 Which of the following materials is used as insulation in high‑voltage capacitors due to its high dielectric strength?
Polyethylene
Glass
Aluminum
Copper
Explanation - Glass provides high dielectric strength for capacitor insulation.
Correct answer is: Glass
Q.92 In high‑voltage engineering, what is the primary function of a 'residual voltage tester'?
To measure the dielectric loss
To check the residual voltage after power removal
To test the magnetic field
To measure the temperature rise
Explanation - Residual voltage testers ensure no dangerous voltage remains after isolation.
Correct answer is: To check the residual voltage after power removal
Q.93 Which of the following is NOT a typical application of a spark gap?
Voltage regulation
Switching device
Insulation material
Voltage limiter
Explanation - A spark gap is a switching device, not an insulator.
Correct answer is: Insulation material
Q.94 Which of these is the primary cause of dielectric breakdown in a solid polymer under high temperature?
Increased conductivity of the polymer
Decrease in dielectric constant
Formation of micro‑cracks
Decrease in thermal conductivity
Explanation - Heat can cause micro‑cracks, which lower the breakdown voltage.
Correct answer is: Formation of micro‑cracks
Q.95 Which of these properties is most critical for a high‑voltage insulating material?
Electrical conductivity
Thermal conductivity
Dielectric strength
Magnetic permeability
Explanation - Dielectric strength is the primary metric for insulation performance.
Correct answer is: Dielectric strength
Q.96 What is the main reason for using a 'silicone elastomer' in high‑voltage insulators?
It has high electrical conductivity
It has a low dielectric constant
It offers high dielectric strength and mechanical flexibility
It is magnetic
Explanation - Silicone elastomers are used for their electrical and mechanical properties.
Correct answer is: It offers high dielectric strength and mechanical flexibility
Q.97 Which of these phenomena is described by the 'electrostriction' effect?
Mechanical deformation due to electric field
Thermal expansion due to current
Magnetic field induced by voltage
Dielectric constant variation with temperature
Explanation - Electrostriction refers to deformation of a material under an electric field.
Correct answer is: Mechanical deformation due to electric field
Q.98 Which of the following best describes a 'high‑voltage arc suppression device'?
A device that increases voltage
A device that clamps voltage during a surge
A device that reduces dielectric strength
A device that increases magnetic field
Explanation - Arc suppression devices limit the voltage to protect insulation.
Correct answer is: A device that clamps voltage during a surge
Q.99 In the context of dielectric breakdown, what does the term 'arc flash' refer to?
A sudden increase in resistance
A high‑energy discharge that can cause injury
A low‑voltage spark
A magnetic field anomaly
Explanation - Arc flash is a dangerous, high‑energy event resulting from a large current surge.
Correct answer is: A high‑energy discharge that can cause injury
Q.100 Which of these is an example of a 'high‑voltage insulator' in power distribution systems?
Copper busbar
Polyethylene cable sheath
Steel tower
Aluminum conductor
Explanation - Polyethylene sheaths provide high‑voltage insulation for cables.
Correct answer is: Polyethylene cable sheath
Q.101 What is a 'dielectric film' commonly used for in electronic devices?
Conducting current
Insulating between circuit layers
Generating magnetic fields
Sensing temperature
Explanation - Dielectric films prevent electrical leakage between layers.
Correct answer is: Insulating between circuit layers
Q.102 Which of these materials is most prone to dielectric breakdown in humid environments?
Silicone
Glass
Polypropylene
PVC
Explanation - PVC’s dielectric strength can degrade more quickly in humid conditions.
Correct answer is: PVC
Q.103 Which of the following is a characteristic of 'soft dielectric' materials?
High dielectric strength
Low dielectric loss
High mechanical flexibility
Low thermal stability
Explanation - Soft dielectrics are flexible but usually have lower dielectric strength.
Correct answer is: High mechanical flexibility
Q.104 What is the primary safety consideration when operating equipment near the dielectric breakdown threshold?
Ensure a low humidity environment
Use the highest possible voltage
Maintain a safety margin below the breakdown voltage
Avoid using insulating materials
Explanation - A safety margin prevents accidental breakdown.
Correct answer is: Maintain a safety margin below the breakdown voltage
Q.105 Which of the following best explains the 'temperature coefficient of dielectric strength'?
It indicates how dielectric strength changes with temperature
It indicates how the dielectric constant changes with temperature
It indicates the thermal expansion rate
It indicates the magnetic susceptibility with temperature
Explanation - The temperature coefficient reflects how dielectric strength varies as temperature changes.
Correct answer is: It indicates how dielectric strength changes with temperature
Q.106 Which of the following is a common method to prevent dielectric breakdown in high‑voltage cables?
Increasing the cable diameter
Adding a conductive shield
Using high‑purity insulating material
Increasing the ambient temperature
Explanation - High purity reduces defects and improves dielectric strength.
Correct answer is: Using high‑purity insulating material
Q.107 Which of the following is the typical breakdown voltage of air at standard temperature and pressure?
3 kV/mm
30 kV/mm
300 kV/mm
3000 kV/mm
Explanation - Air typically has a dielectric strength around 30 kV/mm at STP.
Correct answer is: 30 kV/mm
Q.108 Which of these is a typical test for detecting partial discharges?
Resistance measurement
Acoustic emission detection
Magnetic flux measurement
Thermal imaging
Explanation - Partial discharges produce acoustic signals that can be detected.
Correct answer is: Acoustic emission detection
Q.109 Which of these materials is typically used for high‑voltage busbar insulation?
Aluminum
Copper
PVC
Steel
Explanation - PVC is often used to insulate busbars due to its dielectric properties.
Correct answer is: PVC
Q.110 Which of the following is a typical consequence of dielectric breakdown in a transformer?
Increase in insulation resistance
Reduction in core temperature
Failure of insulation and potential fire
Improvement of oil purity
Explanation - Breakdown leads to short circuits and possible fire hazards.
Correct answer is: Failure of insulation and potential fire
Q.111 What is the primary role of a 'fused barrier' in high‑voltage systems?
To increase voltage
To prevent over‑current
To reduce dielectric strength
To generate magnetic fields
Explanation - Fused barriers protect circuits from over‑current, limiting damage.
Correct answer is: To prevent over‑current
Q.112 Which of the following best describes a 'dielectric fluid' used in switchgear?
A conducting liquid
A non‑conducting liquid with high dielectric strength
A solid polymer
A gas
Explanation - Dielectric fluids like oil provide insulation and cooling.
Correct answer is: A non‑conducting liquid with high dielectric strength
Q.113 Which of these factors is NOT a major consideration in designing high‑voltage insulating systems?
Dielectric strength
Thermal management
Magnetic permeability
Mechanical robustness
Explanation - Dielectric design focuses on electrical and thermal aspects, not magnetic permeability.
Correct answer is: Magnetic permeability