Q.1 What is the primary cause of corona discharge on high‑voltage conductors?
Insulating material degradation
High electric field at conductor surface
Mechanical vibration of the conductor
Thermal expansion of the conductor
Explanation - Corona discharge occurs when the electric field at the surface of a conductor exceeds the breakdown strength of the surrounding air, ionizing the air molecules and producing a visible glow.
Correct answer is: High electric field at conductor surface
Q.2 Paschen's Law describes the relationship between which two parameters?
Voltage and temperature
Pressure and distance
Voltage and distance
Temperature and pressure
Explanation - Paschen's Law gives the breakdown voltage as a function of the product of gas pressure and electrode gap distance, essential for predicting corona inception.
Correct answer is: Voltage and distance
Q.3 Which of the following is NOT a typical effect of corona discharge?
Electrical loss in the system
Emission of ultraviolet radiation
Generation of ozone
Increase in conductor temperature
Explanation - Corona discharge causes electrical loss, UV radiation, and ozone generation but does not significantly raise the conductor temperature as the energy is dissipated in the surrounding air.
Correct answer is: Increase in conductor temperature
Q.4 What is the typical frequency range of radio frequency interference (RFI) caused by high‑voltage switching devices?
30 kHz – 300 kHz
300 kHz – 3 MHz
3 MHz – 30 MHz
30 MHz – 300 MHz
Explanation - Switching transients in high‑voltage equipment primarily generate RFI in the 3–30 MHz range, overlapping with many communication bands.
Correct answer is: 3 MHz – 30 MHz
Q.5 Which component is commonly used on high‑voltage cables to suppress corona discharge?
Coronally‑shielded sheath
Corona ring
Grounding conductor
Spiral cable core
Explanation - Corona rings, often toroidal or annular, are installed at high‑voltage points to distribute the electric field and reduce corona inception.
Correct answer is: Corona ring
Q.6 The corona inception voltage (CIV) for dry air at 1 atm is approximately:
10 kV/m
30 kV/m
70 kV/m
120 kV/m
Explanation - Dry air at standard conditions has a CIV of about 70 kV/m; humidity and temperature variations can significantly lower it.
Correct answer is: 70 kV/m
Q.7 Which of these gases has the lowest corona inception voltage?
Dry air
Nitrogen
Oxygen
Argon
Explanation - Nitrogen, being the main component of air, has a lower CIV than oxygen or argon, making it more prone to corona under the same electric field.
Correct answer is: Nitrogen
Q.8 What is a common symptom of excessive corona in power transmission lines?
Rapid sagging of conductors
Increase in line impedance
Blue‑white glow around conductors
Magnetic field distortion
Explanation - The blue‑white glow is the visible manifestation of ionized air and ozone generation due to corona.
Correct answer is: Blue‑white glow around conductors
Q.9 Which phenomenon can be considered a form of RFI originating from high‑voltage lines?
Capacitively‑coupled hum
Ground‑return voltage
Inductive coupling of harmonics
All of the above
Explanation - High‑voltage lines can radiate RFI through various coupling mechanisms, including capacitance, induction, and voltage drop along the line.
Correct answer is: All of the above
Q.10 Which type of insulation is most effective at suppressing corona under high humidity?
Solid polyethylene
Paper insulation
Oil‑filled paper
Aluminium foil
Explanation - Oil provides a high dielectric strength and reduces moisture penetration, lowering the likelihood of corona at high humidity.
Correct answer is: Oil‑filled paper
Q.11 Which design consideration reduces corona losses in a high‑voltage transformer?
Increasing the core size
Using a higher winding pitch
Reducing the dielectric constant of the core
Increasing the number of turns on the primary
Explanation - A larger winding pitch lowers the surface electric field intensity, thereby reducing corona inception and losses.
Correct answer is: Using a higher winding pitch
Q.12 What is the typical UV wavelength emitted by corona discharge?
200–300 nm
300–400 nm
400–500 nm
500–600 nm
Explanation - Corona discharge emits UV radiation predominantly in the 200–300 nm range, which can degrade polymer insulators.
Correct answer is: 200–300 nm
Q.13 Which factor has the greatest influence on corona inception voltage?
Conductor diameter
Air temperature
Humidity level
Conductor surface roughness
Explanation - Humidity significantly reduces the breakdown voltage of air by increasing conductivity, thus lowering the corona inception voltage.
Correct answer is: Humidity level
Q.14 How can RFI from high‑voltage lines be mitigated in nearby radio receivers?
Using ferrite chokes on input lines
Increasing the antenna gain
Shortening the receiver power supply
Adding a metal shield around the receiver
Explanation - Ferrite chokes suppress high‑frequency currents, reducing RFI coupling into the receiver’s signal path.
Correct answer is: Using ferrite chokes on input lines
Q.15 Which of the following best describes a corona ring's function?
It increases the mechanical strength of the conductor
It reduces the electric field concentration at sharp points
It acts as a thermal sink for the conductor
It provides a path for lightning strikes
Explanation - By distributing the electric field over a larger surface area, a corona ring lowers the likelihood of corona formation at sharp edges.
Correct answer is: It reduces the electric field concentration at sharp points
Q.16 What is the main mechanism by which high‑voltage switching causes RFI?
Thermal expansion of conductors
Rapid voltage changes generating high‑frequency harmonics
Mechanical vibrations of the power lines
Chemical reactions in the insulation
Explanation - Fast switching creates abrupt voltage steps that generate high‑frequency harmonics, which radiate as RFI.
Correct answer is: Rapid voltage changes generating high‑frequency harmonics
Q.17 Which frequency band is most vulnerable to interference from high‑voltage line corona?
HF (3–30 MHz)
VHF (30–300 MHz)
UHF (300 MHz–3 GHz)
Microwave (3–30 GHz)
Explanation - Corona discharge emits strongly in the HF band, overlapping with many radio services and causing interference.
Correct answer is: HF (3–30 MHz)
Q.18 Which environmental condition is least likely to increase corona losses?
High temperature
Low pressure
High humidity
Low humidity
Explanation - Low humidity increases air dielectric strength, reducing corona initiation; high humidity lowers it.
Correct answer is: Low humidity
Q.19 The term 'corona loss' refers to:
Loss of mechanical strength due to corona erosion
Electrical power loss due to corona discharge
Loss of voltage at the end of a transmission line
Loss of signal quality in radio communication
Explanation - Corona loss is the unwanted dissipation of electrical energy into the surrounding air during corona discharge.
Correct answer is: Electrical power loss due to corona discharge
Q.20 Which design technique lowers the corona inception voltage on a high‑voltage bus?
Increasing the conductor diameter
Adding a thin dielectric layer
Using a thicker copper alloy
Applying a magnetic shielding layer
Explanation - A larger diameter reduces the surface electric field for a given voltage, thereby increasing the corona inception voltage.
Correct answer is: Increasing the conductor diameter
Q.21 What is the primary health hazard associated with prolonged exposure to corona-generated ozone?
Skin irritation
Respiratory irritation
Eye damage
Headaches
Explanation - Ozone is a strong oxidant that irritates the respiratory tract, causing coughing, throat irritation, and breathing difficulties.
Correct answer is: Respiratory irritation
Q.22 Which of these methods is NOT commonly used to measure corona power loss?
High‑frequency current transformer (HFCT)
Thermal imaging camera
Voltage divider
Spectrum analyzer
Explanation - Voltage dividers measure voltage, not corona loss; corona loss is detected via HFCT, thermal imaging, or spectrum analysis.
Correct answer is: Voltage divider
Q.23 The term 'corona ring' was originally developed by:
James Clerk Maxwell
Alexander Graham Bell
Sir William Henry Bragg
Carl Friedrich Gauss
Explanation - Bell introduced the corona ring concept in the late 1800s to mitigate corona effects on telegraph lines.
Correct answer is: Alexander Graham Bell
Q.24 Which of the following is a typical symptom of RFI affecting radio receivers?
Blue‑white glow near the antenna
Humming or clicking noise in audio output
Visible corona on power lines
Increased line sag
Explanation - RFI can appear as audible noise in receivers, such as hum or clicks, due to unwanted high‑frequency components.
Correct answer is: Humming or clicking noise in audio output
Q.25 What is the main purpose of using a corona shield on high‑voltage substations?
Prevent lightning strikes
Reduce electromagnetic interference
Improve aesthetic appearance
Provide mechanical support
Explanation - Corona shields lower the electric field intensity, reducing corona-induced electromagnetic interference with nearby equipment.
Correct answer is: Reduce electromagnetic interference
Q.26 Which of the following materials has the highest dielectric strength in air?
Water
Dry air
Oxygen
Nitrogen
Explanation - Dry air possesses a dielectric strength of ~30 kV/cm; water has a much lower strength due to its conductivity.
Correct answer is: Dry air
Q.27 Which phenomenon is most likely to cause radio interference from high‑voltage transmission lines?
Capacitive coupling of low‑frequency hum
Inductive coupling of harmonics
Direct conduction through the ground
Thermal radiation
Explanation - Harmonic currents in high‑voltage lines induce high‑frequency voltage in nearby conductors, producing radio interference.
Correct answer is: Inductive coupling of harmonics
Q.28 Which parameter is NOT typically listed in corona ring specifications?
Outer diameter
Material hardness
Tolerances for surface finish
Electrical conductivity
Explanation - Corona rings are primarily designed for shape and material; their electrical conductivity is not critical as they are non‑conductive.
Correct answer is: Electrical conductivity
Q.29 Which of the following is a common method to reduce corona losses in power lines?
Installing additional grounding electrodes
Using lower voltage lines
Applying a thicker dielectric coating
Increasing the frequency of operation
Explanation - A thicker dielectric coating reduces surface field intensity, thereby lowering corona initiation and losses.
Correct answer is: Applying a thicker dielectric coating
Q.30 Which of the following best explains why corona discharge increases at lower pressures?
Air molecules are more closely spaced
Air molecules are less densely packed, requiring less energy to ionize
Higher pressure increases dielectric strength
Lower pressure increases the conductivity of air
Explanation - At lower pressure, fewer molecules mean a lower breakdown voltage; thus corona can initiate at lower electric fields.
Correct answer is: Air molecules are less densely packed, requiring less energy to ionize
Q.31 Which type of radiation is most dangerous to aircraft flying near high‑voltage lines?
Infrared
Visible light
Ultraviolet
X‑ray
Explanation - UV radiation from corona can cause eye irritation and damage to materials, posing risks for aircraft and maintenance personnel.
Correct answer is: Ultraviolet
Q.32 What is the typical frequency of the 'click' noise heard in radio receivers near high‑voltage lines?
50 Hz
60 Hz
500 Hz
5 kHz
Explanation - The click noise is often due to high‑frequency switching components generating harmonics around several kilohertz.
Correct answer is: 5 kHz
Q.33 Which of the following is a major consequence of corona on power transmission efficiency?
Increased line resistance
Reduced power factor
Decreased voltage drop
Higher transmission voltage
Explanation - Corona loss effectively adds a resistive component to the line, reducing the overall efficiency of power transmission.
Correct answer is: Increased line resistance
Q.34 Which type of transformer winding arrangement helps reduce corona loss?
Windings with tight spacing
Windings with large pitch
Windings with fewer turns
Windings with a laminated core
Explanation - Large pitch spacing reduces surface field intensity and thereby decreases corona inception probability.
Correct answer is: Windings with large pitch
Q.35 What is the primary reason that corona rings are often made from ceramic materials?
High thermal conductivity
Low electrical conductivity
High mechanical strength
Good dielectric properties
Explanation - Ceramic materials have excellent dielectric strength and can withstand high electric fields without conduction.
Correct answer is: Good dielectric properties
Q.36 Which of the following best describes a corona discharge's spectral emissions?
Broadband radio waves
Visible light with UV emission
Only infrared emission
Only acoustic emission
Explanation - Corona produces a characteristic blue‑white glow (visible) and emits ultraviolet radiation due to ionized air.
Correct answer is: Visible light with UV emission
Q.37 Which of these is a typical RFI mitigation technique used on high‑voltage substations?
Installing lightning rods
Adding ferrite cores to cable feedthroughs
Increasing the clearance between conductors
Using high‑temperature insulating materials
Explanation - Ferrite cores suppress high‑frequency currents in cable feedthroughs, reducing radiated RFI.
Correct answer is: Adding ferrite cores to cable feedthroughs
Q.38 Which phenomenon is responsible for the 'blue glow' seen at high‑voltage equipment?
Ozone combustion
Ionized nitrogen and oxygen
Heating of the air
Light scattering by dust particles
Explanation - The glow originates from excited nitrogen and oxygen molecules returning to ground state, emitting blue‑white light.
Correct answer is: Ionized nitrogen and oxygen
Q.39 The 'inception voltage' refers to:
Voltage at which a device ignites
Voltage at which a conductor starts to corrode
Voltage at which corona discharge begins
Voltage at which the power system is initiated
Explanation - Inception voltage is the threshold at which the electric field causes ionization of the surrounding gas, initiating corona.
Correct answer is: Voltage at which corona discharge begins
Q.40 Which of the following is NOT a typical symptom of RFI on a radio receiver?
Loss of signal clarity
Increased audio distortion
Physical damage to the antenna
Presence of a hum in the audio output
Explanation - RFI mainly degrades signal quality; it does not physically damage the antenna.
Correct answer is: Physical damage to the antenna
Q.41 Which of these is a key factor determining corona inception voltage in dry air at room temperature?
Conductor temperature
Air humidity
Atmospheric pressure
Both B and C
Explanation - Humidity and pressure affect air breakdown; lower humidity and pressure increase corona inception voltage.
Correct answer is: Both B and C
Q.42 Which type of high‑frequency filter is commonly used to protect radio receivers from RFI originating from power lines?
Low‑pass filter
Band‑stop filter
High‑pass filter
All of the above
Explanation - Band‑stop (notch) filters suppress specific interference frequencies while allowing desired signals to pass.
Correct answer is: Band‑stop filter
Q.43 Which of the following statements about ozone formation in corona discharge is FALSE?
Ozone is produced from molecular oxygen
Ozone levels increase with corona intensity
Ozone is harmless at all concentrations
Ozone can damage polymer insulators
Explanation - Ozone is a toxic gas at relatively low concentrations and can corrode insulators and pose health risks.
Correct answer is: Ozone is harmless at all concentrations
Q.44 What is the approximate ratio of corona power loss to total line loss at 400 kV in typical transmission lines?
1–2 %
5–7 %
10–12 %
20–25 %
Explanation - Corona loss is usually a small fraction (1–2 %) of total line loss in well‑designed 400 kV lines.
Correct answer is: 1–2 %
Q.45 Which of the following is a primary reason for installing a corona ring on a high‑voltage cable termination?
To increase the mechanical strength
To reduce the electric field at the termination
To improve the cable's thermal performance
To provide a lightning protection path
Explanation - Corona rings spread the electric field over a larger surface, preventing localized corona initiation.
Correct answer is: To reduce the electric field at the termination
Q.46 Which of these components is most likely to generate RFI due to high‑frequency switching?
Power factor correction capacitor
Silicon controlled rectifier (SCR)
Inductively coupled coil
Metallic bus bar
Explanation - SCRs switch rapidly, producing high‑frequency harmonics that can radiate as RFI.
Correct answer is: Silicon controlled rectifier (SCR)
Q.47 Which type of dielectric material is most effective at reducing corona when used as a coating on high‑voltage conductors?
Polyethylene terephthalate (PET)
Polyvinyl chloride (PVC)
Polyurethane
Polyethylene
Explanation - Polyethylene has high dielectric strength and low moisture absorption, making it ideal for corona suppression.
Correct answer is: Polyethylene
Q.48 What is a typical method for measuring the corona inception voltage on a test stand?
Measuring the UV output
Using a high‑voltage probe and a ramp
Recording the audible click sound
Measuring the ozone concentration
Explanation - A voltage ramp applied to the probe while monitoring corona onset provides the inception voltage.
Correct answer is: Using a high‑voltage probe and a ramp
Q.49 Which of the following is a characteristic of a corona ring's shape?
Flat disc
Spherical
Toroidal
Rectangular
Explanation - Toroidal or annular shapes distribute electric fields evenly, making them effective as corona rings.
Correct answer is: Toroidal
Q.50 The 'critical electric field' for corona in dry air is roughly:
1 kV/mm
10 kV/mm
30 kV/mm
70 kV/mm
Explanation - The critical field in dry air is about 70 kV per millimeter (70 kV/m for 1 mm).
Correct answer is: 70 kV/mm
Q.51 Which of the following is NOT a direct effect of corona on equipment?
Erosion of conductor surface
Generation of audible noise
Production of ozone
Increase in system reliability
Explanation - Corona generally degrades equipment and reliability, not improves it.
Correct answer is: Increase in system reliability
Q.52 What is the main advantage of using a 'graded corona ring' design?
Uniform field distribution
Reduced cost
Simplified installation
Enhanced mechanical strength
Explanation - Graded corona rings provide a gradual change in electric field, minimizing local high‑field spots.
Correct answer is: Uniform field distribution
Q.53 Which of the following best explains why corona can be more intense at night?
Temperature rises
Humidity is lower
Air becomes denser
Conductor heats up
Explanation - Lower humidity increases air dielectric strength, reducing corona, but at night, temperature drops and humidity can increase; thus corona can be more intense if humidity is high.
Correct answer is: Humidity is lower
Q.54 What is the primary source of electromagnetic interference (EMI) in high‑voltage circuits?
Thermal gradients
Switching transients
Mechanical stress
Corrosion products
Explanation - Rapid voltage and current changes generate high‑frequency EMI, which can interfere with nearby electronics.
Correct answer is: Switching transients
Q.55 Which of the following is a typical application for high‑frequency current transformers (HFCT) in corona measurement?
Measuring DC current
Detecting high‑frequency switching noise
Measuring voltage drop across a resistor
Determining line impedance
Explanation - HFCTs are used to capture high‑frequency components associated with corona and switching noise.
Correct answer is: Detecting high‑frequency switching noise
Q.56 Which of these is a typical symptom of ozone damage in polymer insulators?
Surface cracking
Color change to blue
Increased dielectric strength
Reduced thermal resistance
Explanation - Ozone can cause surface degradation, leading to cracking and reduced insulating performance.
Correct answer is: Surface cracking
Q.57 Which component is commonly used to provide a controlled discharge path in high‑voltage test setups?
Spark gap
Fuse
Thermal resistor
Capacitor bank
Explanation - Spark gaps provide a known, repeatable discharge path for measuring corona inception and arc behavior.
Correct answer is: Spark gap
Q.58 What is the effect of increasing the clearance between conductors on corona formation?
Increases corona initiation
Decreases corona initiation
No effect
Changes frequency of corona discharge
Explanation - Higher clearance reduces electric field concentration, raising corona inception voltage and reducing corona occurrence.
Correct answer is: Decreases corona initiation
Q.59 Which of the following best describes the term 'corona loss factor'?
Ratio of corona loss to line resistance
Ratio of corona loss to total line loss
Ratio of corona power to total power
Ratio of corona voltage to system voltage
Explanation - Corona loss factor is a dimensionless quantity indicating the fraction of total losses due to corona.
Correct answer is: Ratio of corona loss to total line loss
Q.60 Which of the following is a typical mitigation strategy for RFI in high‑voltage substation control rooms?
Installing thick concrete walls
Using shielded twisted‑pair cables
Increasing line voltage
Installing more transformers
Explanation - Shielded twisted‑pair cables reduce inductive and capacitive coupling of high‑frequency RFI.
Correct answer is: Using shielded twisted‑pair cables
Q.61 Which of the following best describes a 'corona discharge loop'?
A loop that stabilizes the electric field around a conductor
A loop formed by a corona ring and ground
A loop that directs ozone away from insulators
A loop that prevents lightning strikes
Explanation - A corona ring provides a controlled discharge path that forms a loop with the ground, preventing uncontrolled arcs.
Correct answer is: A loop formed by a corona ring and ground
Q.62 Which type of conductor surface finish is most effective at reducing corona initiation?
Polished
Roughened
Painted
Insulated
Explanation - Smooth surfaces reduce field enhancements due to microscopic protrusions, lowering corona inception.
Correct answer is: Polished
Q.63 Which phenomenon is a direct result of the high electric field at the tip of a conductor?
Lightning initiation
Corona discharge
Capacitive heating
Thermal expansion
Explanation - High electric field at a sharp tip causes ionization of surrounding air, leading to corona discharge.
Correct answer is: Corona discharge
Q.64 Which of the following is NOT a common measurement unit for corona loss?
Watts
Decibels
Amperes
Volts
Explanation - Decibels measure logarithmic ratios of power or voltage, not direct corona loss values.
Correct answer is: Decibels
Q.65 Which factor is most significant in determining the 'inception angle' of a corona ring?
Ring material
Ring radius
Ambient temperature
Humidity
Explanation - Ring radius directly influences the electric field distribution and thus the inception angle.
Correct answer is: Ring radius
Q.66 What is the typical magnitude of RFI voltage observed on a telephone line near a high‑voltage line?
Below 0.1 V
0.1–1 V
1–10 V
Above 10 V
Explanation - RFI on telephone lines typically appears as low‑level voltages in the 0.1–1 V range.
Correct answer is: 0.1–1 V
Q.67 Which of the following is a typical effect of corona on the environment?
Decreases air pollution
Increases ozone concentration
Reduces greenhouse gases
Improves air quality
Explanation - Corona discharges produce ozone, contributing to air pollution if not controlled.
Correct answer is: Increases ozone concentration
Q.68 Which type of connector is often used in high‑voltage testing equipment to avoid corona formation?
Ball‑and‑socket connector
Screw‑type connector
Spade‑connector
Soldered joint
Explanation - Ball‑and‑socket connectors provide a smooth contact surface that reduces field concentration.
Correct answer is: Ball‑and‑socket connector
Q.69 Which of the following is a primary consideration when designing a high‑voltage transformer to minimize corona?
Use of thick copper windings
Increasing the air gap
Optimizing winding pitch
Using a steel core
Explanation - Larger winding pitch reduces surface electric fields, lowering corona inception.
Correct answer is: Optimizing winding pitch
Q.70 Which of the following is a typical sign of corona interference in a radio communications system?
Blue‑white glow near antennas
Audio hiss or clicking noise
Loss of power supply
Physical corrosion of components
Explanation - Corona-related RFI often manifests as audible noise in radio receivers.
Correct answer is: Audio hiss or clicking noise
Q.71 Which of the following is a typical method to reduce corona loss in a high‑voltage cable?
Installing a thicker copper sheath
Adding a corona ring around the cable
Increasing the cable temperature
Using a lower dielectric material
Explanation - Corona rings spread the electric field over a larger area, mitigating corona loss.
Correct answer is: Adding a corona ring around the cable
Q.72 Which of the following best explains the 'blue‑white glow' around high‑voltage conductors?
Incandescence from heating
Emission from ionized nitrogen and oxygen
Reflection of ambient light
Fluorescence of the conductor coating
Explanation - The glow arises from excited air molecules emitting light as they return to lower energy states.
Correct answer is: Emission from ionized nitrogen and oxygen
Q.73 Which of these is NOT typically used as a corona suppressant material?
Ceramic
Glass
Wood
Polyethylene
Explanation - Wood has lower dielectric strength and higher moisture absorption, making it unsuitable for corona suppression.
Correct answer is: Wood
Q.74 What is the typical effect of high humidity on corona inception voltage?
It increases the voltage
It decreases the voltage
It has no effect
It reverses the polarity
Explanation - Higher humidity reduces air breakdown strength, leading to a lower corona inception voltage.
Correct answer is: It decreases the voltage
Q.75 Which of the following is a common design parameter for a corona ring?
Diameter
Thickness
Material composition
All of the above
Explanation - Corona ring design involves diameter, thickness, and material to meet dielectric and field requirements.
Correct answer is: All of the above
Q.76 Which of these is a typical source of RFI in a high‑voltage substation?
Motor drives
Lightning strikes
Static discharge
All of the above
Explanation - All listed sources can produce RFI due to rapid voltage or current changes.
Correct answer is: All of the above
Q.77 What is a common diagnostic tool for measuring corona loss in a transmission line?
High‑frequency current transformer (HFCT)
Thermographic camera
Ozone meter
All of the above
Explanation - Each instrument detects different aspects of corona: HFCT captures high‑frequency currents, thermographic imaging shows heating, and ozone meters measure chemical byproducts.
Correct answer is: All of the above
Q.78 Which of the following best explains the 'inception angle' of a corona ring?
The angle at which the ring begins to conduct electricity
The angular range over which corona initiates around the ring
The angle between the ring and the ground
The angle of the ring’s cross‑section
Explanation - Inception angle refers to the portion of the ring circumference where corona starts to form.
Correct answer is: The angular range over which corona initiates around the ring
Q.79 Which of these is a typical symptom of high‑frequency noise in a radio receiver?
Loss of power supply
Interference in audio output
Physical damage to the speaker
Increased signal latency
Explanation - High‑frequency noise often appears as static or hiss in audio signals.
Correct answer is: Interference in audio output
Q.80 Which of the following is a common method to reduce RFI from a high‑voltage transformer?
Adding a magnetic shield
Shortening the transformer leads
Using a higher voltage transformer
Increasing the transformer size
Explanation - Magnetic shields reduce inductive coupling of high‑frequency currents, decreasing RFI.
Correct answer is: Adding a magnetic shield
Q.81 Which phenomenon causes 'click' noise on a radio receiver when near a high‑voltage line?
Capacitive coupling of the line's AC voltage
Rapid discharge of corona
Thermal expansion of the cable
Mechanical vibration of the antenna
Explanation - Corona discharge can produce audible clicks when it discharges abruptly in the radio receiver's circuitry.
Correct answer is: Rapid discharge of corona
Q.82 Which of the following is an indication of corona damage on an insulator?
Smooth surface
Surface pitting
Color change to white
Uniform thickness
Explanation - Corona erosion creates microscopic pits and cracks on the insulator surface.
Correct answer is: Surface pitting
Q.83 Which of the following best describes the relationship between corona loss and line voltage?
Coronal loss decreases with increasing voltage
Coronal loss is independent of voltage
Coronal loss increases with increasing voltage
Coronal loss is only affected by current
Explanation - Higher voltage raises the electric field intensity, promoting corona formation and increasing loss.
Correct answer is: Coronal loss increases with increasing voltage
Q.84 Which of these is a typical RFI mitigation technique for low‑frequency communication systems?
Installing a ground plane
Adding a ferrite bead to the power line
Using a high‑voltage transformer
Increasing the power supply voltage
Explanation - Ferrite beads suppress high‑frequency noise that can couple into low‑frequency communication lines.
Correct answer is: Adding a ferrite bead to the power line
Q.85 Which of the following is NOT a direct result of ozone production in corona discharge?
Corrosion of metal parts
Degradation of polymer insulation
Improved air quality
Health hazards to humans
Explanation - Ozone is a pollutant that degrades materials and poses health risks; it does not improve air quality.
Correct answer is: Improved air quality
Q.86 Which of the following best explains why corona can be more intense at lower temperatures?
Lower temperature increases air density, raising dielectric strength
Lower temperature decreases air density, reducing dielectric strength
Temperature has no effect on corona
Corona is only affected by humidity
Explanation - Cooler air is less dense, lowering the breakdown voltage and making corona more likely.
Correct answer is: Lower temperature decreases air density, reducing dielectric strength
Q.87 Which of these is a typical measurement for corona discharge in a test system?
UV intensity
Ozone concentration
Acoustic emission
All of the above
Explanation - UV, ozone, and acoustic signals all provide information about corona discharge characteristics.
Correct answer is: All of the above
Q.88 Which of the following best explains why a high‑voltage line can interfere with a radio transmitter?
Through magnetic coupling
Through capacitive coupling
Through both magnetic and capacitive coupling
Both A and B
Explanation - High‑voltage lines can couple interference via both magnetic (inductive) and electric (capacitive) means.
Correct answer is: Both A and B
Q.89 What is the typical effect of corona on the surface temperature of a conductor?
It significantly raises the temperature
It slightly raises the temperature
It lowers the temperature
It has no effect on temperature
Explanation - Corona produces a small amount of heat, raising the conductor temperature marginally.
Correct answer is: It slightly raises the temperature
Q.90 Which of the following is a typical method to mitigate corona in HV transformers?
Using a lower winding pitch
Applying a thicker dielectric layer
Shortening the secondary winding
Increasing the core permeability
Explanation - Reducing winding pitch (i.e., increasing spacing between turns) lowers the surface field, reducing corona.
Correct answer is: Using a lower winding pitch
Q.91 Which of these is NOT a typical symptom of corona in a high‑voltage line?
Blue‑white glow
Ozone odor
High‑frequency noise
Continuous audible humming
Explanation - Corona usually produces intermittent or click noise, not continuous humming.
Correct answer is: Continuous audible humming
Q.92 Which of the following best describes the effect of a corona ring on electric field distribution?
It concentrates the field
It eliminates the field
It distributes the field over a larger area
It reflects the field
Explanation - Corona rings spread the electric field, reducing peak values that cause corona.
Correct answer is: It distributes the field over a larger area
Q.93 Which of these is a typical application of high‑frequency current transformers in HV systems?
Detecting AC losses
Measuring DC current
Measuring high‑frequency noise
Measuring line voltage
Explanation - HFCTs capture high‑frequency components such as corona noise in HV systems.
Correct answer is: Measuring high‑frequency noise
Q.94 What is the typical effect of increasing the size of a corona ring?
It increases corona inception voltage
It decreases corona inception voltage
It has no effect
It increases mechanical strength only
Explanation - A larger corona ring reduces peak surface fields, raising the voltage needed to start corona.
Correct answer is: It increases corona inception voltage
Q.95 Which of the following is a primary cause of radio interference from high‑voltage transmission lines?
Capacitive coupling of lightning strikes
Thermal noise in conductors
Magnetic coupling of harmonics
Mechanical vibrations of the cable
Explanation - High‑frequency harmonics generated by switching cause magnetic coupling interference.
Correct answer is: Magnetic coupling of harmonics
Q.96 Which of the following best describes the purpose of a high‑frequency filter in a radio receiver?
To increase the bandwidth
To eliminate unwanted high‑frequency signals
To boost the signal amplitude
To convert AC to DC
Explanation - High‑frequency filters remove interfering signals outside the desired frequency band.
Correct answer is: To eliminate unwanted high‑frequency signals
Q.97 Which of these is a typical effect of ozone on polymer insulators?
Increases dielectric strength
Causes surface cracking
Reduces thermal conductivity
Improves mechanical strength
Explanation - Ozone attacks the polymer chains, leading to surface degradation and cracking.
Correct answer is: Causes surface cracking
Q.98 Which of the following is a typical method to reduce corona loss in high‑voltage lines?
Using thicker conductors
Increasing the distance between conductors
Installing corona rings
All of the above
Explanation - All listed methods reduce corona initiation by lowering the electric field intensity or increasing dielectric strength.
Correct answer is: All of the above
Q.99 What is the main function of a ferrite choke in RFI mitigation?
To block low‑frequency currents
To attenuate high‑frequency currents
To increase current flow
To dissipate heat
Explanation - Ferrite chokes present high impedance to high‑frequency currents, reducing RFI coupling.
Correct answer is: To attenuate high‑frequency currents
Q.100 Which of these is a typical indicator of high corona loss in a transmission line?
Rapid line sagging
High audible noise
Increased line voltage
Decrease in line resistance
Explanation - Corona generates audible noise, a clear indicator of significant corona loss.
Correct answer is: High audible noise
Q.101 What is the effect of a sharp conductor edge on corona initiation?
It reduces corona initiation
It has no effect
It enhances corona initiation
It changes the corona color
Explanation - Sharp edges concentrate the electric field, lowering the breakdown voltage and promoting corona.
Correct answer is: It enhances corona initiation
Q.102 Which of these is NOT typically considered in the design of a corona suppression system?
Material dielectric strength
Surface roughness
Conductor temperature
Ambient humidity
Explanation - While temperature affects insulation, corona suppression design focuses on dielectric and geometric parameters, not conductor temperature.
Correct answer is: Conductor temperature
Q.103 What is the typical range of voltage rise during a corona discharge event?
Less than 1 V
1–5 V
5–20 V
Above 20 V
Explanation - Corona discharges can produce rapid voltage spikes in the 5–20 V range, disturbing sensitive electronics.
Correct answer is: 5–20 V
Q.104 Which of the following best describes the primary mechanism of RFI generation in high‑voltage lines?
Mechanical vibration of conductors
Capacitive coupling of high‑frequency currents
Thermal expansion of the ground
Magnetostatic induction only
Explanation - High‑frequency currents in the line induce voltage in nearby conductors via capacitive coupling.
Correct answer is: Capacitive coupling of high‑frequency currents
Q.105 Which of these is a typical RFI mitigation method for power electronics?
Using a transformer with low leakage inductance
Applying a high‑frequency filter to the output
Installing a high‑temperature insulator
Using a larger copper conductor
Explanation - High‑frequency filters suppress switching noise that could otherwise radiate as RFI.
Correct answer is: Applying a high‑frequency filter to the output
Q.106 What is the typical color of corona discharge glow in humid conditions?
Blue‑white
Red‑orange
Green
Yellow
Explanation - Even in humid conditions, corona glow remains blue‑white due to the excitation of nitrogen and oxygen.
Correct answer is: Blue‑white
Q.107 Which of the following is a direct measurement technique for corona loss in high‑voltage lines?
Measuring the UV spectrum
Measuring the current waveform with a HFCT
Measuring the temperature rise of the conductor
Measuring the ozone concentration
Explanation - HFCTs capture high‑frequency current components associated with corona, allowing loss estimation.
Correct answer is: Measuring the current waveform with a HFCT
Q.108 Which of the following best describes the effect of humidity on corona inception voltage?
Increases the inception voltage
Decreases the inception voltage
No effect
Reverses polarity
Explanation - Higher humidity lowers the dielectric strength of air, reducing the corona inception voltage.
Correct answer is: Decreases the inception voltage
Q.109 Which of these is a typical RFI symptom in a cellular base station near a HV line?
Signal distortion
Improved battery life
Higher data rates
No impact
Explanation - RFI can distort the base station’s signal, leading to degraded performance.
Correct answer is: Signal distortion
Q.110 What is the primary reason that corona rings are often made from ceramic materials?
High thermal conductivity
Low dielectric loss
High dielectric strength
Low cost
Explanation - Ceramics have high dielectric strength, enabling them to withstand high electric fields without conduction.
Correct answer is: High dielectric strength
Q.111 Which of the following is a typical method to reduce corona in high‑voltage conductors?
Increasing the conductor diameter
Adding a thin metallic coating
Installing a corona ring
All of the above
Explanation - All methods reduce the local electric field, thereby mitigating corona formation.
Correct answer is: All of the above
Q.112 Which of the following best explains why high‑frequency noise can interfere with radio receivers?
It adds a DC offset
It creates a noise floor that masks signals
It improves signal clarity
It reduces the antenna size
Explanation - High‑frequency noise increases the receiver’s noise floor, reducing signal‑to‑noise ratio.
Correct answer is: It creates a noise floor that masks signals
Q.113 Which of these is a typical indicator of corona on a high‑voltage transmission line?
Blue‑white glow
Strong metallic smell
Visible spark gaps
Continuous hum
Explanation - The visible blue‑white glow is the classic sign of corona discharge.
Correct answer is: Blue‑white glow
Q.114 Which of these is a primary concern when installing high‑voltage conductors near residential areas?
Increased noise pollution
Reduced lightning protection
Higher risk of corona and RFI affecting radios
All of the above
Explanation - High‑voltage lines can produce corona and RFI, potentially disrupting household electronics and radios.
Correct answer is: Higher risk of corona and RFI affecting radios
Q.115 Which of the following is NOT typically considered in a corona ring design?
Material dielectric constant
Ring radius
Surface finish
Magnetic permeability
Explanation - Corona ring design focuses on dielectric properties, geometry, and surface finish; magnetic permeability is not relevant.
Correct answer is: Magnetic permeability
Q.116 Which of these is a common method to detect corona in power distribution systems?
Measuring audible hiss
Monitoring ozone concentration
Both A and B
Measuring line sag
Explanation - Corona produces both audible noise and ozone, both of which can be used as detection signals.
Correct answer is: Both A and B
Q.117 Which of the following best describes the relationship between corona loss and temperature?
Corona loss increases with increasing temperature
Corona loss decreases with increasing temperature
Corona loss is independent of temperature
Corona loss depends only on voltage
Explanation - Higher temperatures reduce air density, lowering the breakdown voltage and increasing corona loss.
Correct answer is: Corona loss increases with increasing temperature
Q.118 Which of these is a typical effect of corona on the dielectric material of an insulator?
Increases dielectric strength
Causes surface erosion
Improves thermal resistance
Reduces mechanical strength only
Explanation - Corona erosion removes material from the surface, weakening the dielectric.
Correct answer is: Causes surface erosion
Q.119 What is the main factor limiting the maximum voltage a corona ring can handle?
Mechanical strength
Dielectric strength of the surrounding air
Thermal conductivity
Magnetic permeability
Explanation - The ring’s ability to suppress corona is governed by the surrounding air’s dielectric limits.
Correct answer is: Dielectric strength of the surrounding air
Q.120 Which of the following is a typical RFI mitigation device used in high‑voltage substation control panels?
Ferrite beads
Shielded cables
Grounded chokes
All of the above
Explanation - All listed devices are used to suppress RFI in high‑voltage environments.
Correct answer is: All of the above
Q.121 Which of the following best describes the effect of a corona ring on the electric field gradient?
It increases the gradient
It decreases the gradient
It has no effect
It reverses the direction of the field
Explanation - A corona ring spreads the electric field, lowering its gradient and preventing localized high fields.
Correct answer is: It decreases the gradient
Q.122 What is the typical frequency range for radio interference caused by high‑voltage line harmonics?
50–60 Hz
200 Hz–1 kHz
10 kHz–100 kHz
1 MHz–100 MHz
Explanation - Harmonics from high‑voltage systems usually occupy the 10–100 kHz range.
Correct answer is: 10 kHz–100 kHz
Q.123 Which of the following is a common symptom of corona in high‑voltage cables?
Ozone smell
Blue‑white glow
High‑frequency noise
All of the above
Explanation - Corona discharge produces ozone, visible glow, and high‑frequency noise.
Correct answer is: All of the above
Q.124 Which of these is a typical application of a high‑frequency filter in a radio system?
To remove low‑frequency hum
To remove high‑frequency noise from RFI
To increase signal bandwidth
To amplify the signal
Explanation - High‑frequency filters are used to suppress unwanted high‑frequency interference.
Correct answer is: To remove high‑frequency noise from RFI
Q.125 Which of these is an effect of corona on the line impedance?
Increases line resistance
Decreases line resistance
Has no effect
Changes the line capacitance only
Explanation - Corona introduces a resistive component to the line, raising the overall resistance.
Correct answer is: Increases line resistance
Q.126 Which of these is a common method to reduce ozone generation in high‑voltage systems?
Operating at lower voltage
Using high humidity
Increasing conductor temperature
Adding corona rings
Explanation - Corona rings reduce corona, thereby lowering ozone production.
Correct answer is: Adding corona rings
Q.127 What is the effect of a higher air pressure on corona inception voltage?
It increases the voltage
It decreases the voltage
It has no effect
It causes corona to disappear
Explanation - Higher pressure increases air density, raising breakdown voltage and corona inception voltage.
Correct answer is: It increases the voltage
Q.128 Which of these is a typical indicator of high‑frequency interference on a TV receiver?
Static or snow on the screen
Improved picture quality
Higher contrast
No impact
Explanation - High‑frequency interference often appears as static or snow in the TV image.
Correct answer is: Static or snow on the screen
Q.129 What is the typical color of ozone produced by corona discharge?
Colorless
Blue‑white
Yellow
Green
Explanation - Ozone is a colorless gas; however, it is associated with the blue‑white glow from corona.
Correct answer is: Colorless
Q.130 Which of these is a common effect of corona on power line reliability?
Increases mechanical wear
Reduces voltage drop
Improves insulation life
None of the above
Explanation - Corona causes surface erosion, leading to mechanical degradation of conductors.
Correct answer is: Increases mechanical wear
Q.131 What is a typical measurement technique for detecting corona in power transmission lines?
Using a high‑frequency current transformer
Measuring ozone concentration
Observing UV light emission
All of the above
Explanation - All listed techniques are used to detect and quantify corona in power lines.
Correct answer is: All of the above
Q.132 Which of these is NOT a typical symptom of RFI in a cellular phone?
Dropped calls
Data slowdown
Improved reception
Signal distortion
Explanation - RFI typically degrades reception, not improves it.
Correct answer is: Improved reception
Q.133 Which of these best describes the function of a high‑voltage surge arrester?
To suppress corona
To protect against lightning transients
To reduce RFI
To increase line capacity
Explanation - Surge arresters clamp transient over‑voltages from lightning, not corona suppression.
Correct answer is: To protect against lightning transients
Q.134 Which of the following is a typical effect of ozone on polymer insulators?
Strengthening the polymer
Causing discoloration
Improving dielectric properties
Reducing thermal conductivity
Explanation - Ozone attacks polymers, leading to surface discoloration and degradation.
Correct answer is: Causing discoloration
Q.135 Which of these is a common method to reduce corona on high‑voltage cables?
Adding a thicker outer sheath
Installing a corona ring
Using a higher temperature cable
Both A and B
Explanation - Both increasing sheath thickness and installing corona rings reduce the field concentration.
Correct answer is: Both A and B
Q.136 Which of these is a typical consequence of high corona loss?
Improved system efficiency
Reduced line sag
Increased line resistance
Decreased power consumption
Explanation - Corona loss adds a resistive component, raising the effective line resistance.
Correct answer is: Increased line resistance
Q.137 What is the typical frequency range of RFI caused by high‑voltage switching devices?
50–60 Hz
500 Hz–10 kHz
10 kHz–100 kHz
100 kHz–1 MHz
Explanation - High‑voltage switching generates harmonics in the 10–100 kHz band, which can interfere with radios.
Correct answer is: 10 kHz–100 kHz
Q.138 Which of these is a typical effect of corona on the surrounding environment?
Increase in greenhouse gases
Reduction in ozone
Increase in ozone concentration
Decrease in air pollution
Explanation - Corona discharge produces ozone, increasing atmospheric concentration.
Correct answer is: Increase in ozone concentration
Q.139 Which of the following is a typical RFI source in a high‑voltage substation?
Motor drives
Lightning
Thermal sensors
All of the above
Explanation - All listed sources can generate RFI through rapid voltage or current changes.
Correct answer is: All of the above
Q.140 Which of these is a common method to detect corona in power lines?
Measuring audible noise
Monitoring ozone concentration
Using UV sensors
All of the above
Explanation - All are standard detection methods for corona.
Correct answer is: All of the above
Q.141 Which of these is a typical symptom of high corona loss in a transformer?
Blue‑white glow around the windings
Reduction in core saturation
Lower temperature rise
Improved insulation life
Explanation - Visible glow is a clear sign of corona in transformer windings.
Correct answer is: Blue‑white glow around the windings
Q.142 What is a typical effect of high humidity on corona inception voltage?
Increases the voltage
Decreases the voltage
No effect
Reverses polarity
Explanation - Higher humidity lowers the dielectric strength of air, reducing corona inception voltage.
Correct answer is: Decreases the voltage
Q.143 Which of the following best describes the purpose of a corona ring?
To increase conductor strength
To reduce electric field concentration
To enhance thermal dissipation
To provide lightning protection
Explanation - Corona rings distribute the electric field, preventing localized high‑field corona formation.
Correct answer is: To reduce electric field concentration
Q.144 Which of the following is a typical RFI mitigation technique for power lines?
Installing additional grounding rods
Using high‑frequency ferrite cores
Increasing conductor diameter
All of the above
Explanation - Grounding, ferrite cores, and larger conductors all help reduce RFI from power lines.
Correct answer is: All of the above
Q.145 Which of these is a typical symptom of corona in a high‑voltage transmission line?
Blue‑white glow
Ozone odor
High‑frequency noise
All of the above
Explanation - All listed symptoms indicate corona discharge in a high‑voltage line.
Correct answer is: All of the above
Q.146 Which of these is a typical method to reduce corona in a high‑voltage cable?
Adding a thicker copper sheath
Installing a corona ring
Using a higher temperature cable
Both A and B
Explanation - Increasing the sheath diameter and installing a corona ring both lower the electric field concentration.
Correct answer is: Both A and B
Q.147 Which of these is a typical effect of corona on a high‑voltage transformer?
Increased core saturation
Higher noise level
Reduced operating temperature
Improved insulation life
Explanation - Corona causes high‑frequency noise that can be heard as a hiss or click in transformers.
Correct answer is: Higher noise level
Q.148 Which of the following is a typical method to detect corona in high‑voltage transmission lines?
Using an ultraviolet camera
Measuring line voltage
Monitoring line sag
All of the above
Explanation - UV cameras detect the characteristic blue‑white glow of corona, providing visual confirmation.
Correct answer is: Using an ultraviolet camera