Q.1 What is the primary purpose of a high voltage insulation resistance tester?
To measure the dielectric strength of a material
To determine the leakage current in a circuit
To test the insulation resistance between conductors
To assess the corona inception voltage
Explanation - A megohmmeter (insulation resistance tester) applies a high DC voltage to a pair of conductors and measures the resulting current to calculate insulation resistance.
Correct answer is: To test the insulation resistance between conductors
Q.2 Which of the following is NOT a typical criterion for a successful dielectric withstand test?
No significant current increase during the test
Absence of sparking or flashover
No audible arcing noise
The test voltage must be at least 1.5 times the rated voltage
Explanation - Dielectric withstand tests focus on current rise, sparking, and flashover. Audible arcing may occur even if the test passes.
Correct answer is: No audible arcing noise
Q.3 What is the typical frequency range of a high voltage surge generator used for surge testing?
10 Hz – 100 Hz
50 Hz – 60 Hz
0.5 kHz – 10 kHz
50 kHz – 150 kHz
Explanation - Surge generators produce fast pulses (~50–150 kHz rise time) to simulate lightning or switching surges.
Correct answer is: 50 kHz – 150 kHz
Q.4 During a partial discharge (PD) test, the PD signal is typically measured in which unit?
Volts
Amps
Microfarads
Pulses per second
Explanation - PD activity is quantified as counts of discharge pulses per unit time (e.g., pps or pulses per minute).
Correct answer is: Pulses per second
Q.5 Which parameter is most critical when selecting a dielectric withstand tester for high voltage cables?
Voltage rating of the tester
Test frequency
Maximum test time
Current measuring range
Explanation - The tester voltage must exceed the rated voltage of the cable by a safety margin.
Correct answer is: Voltage rating of the tester
Q.6 The corona inception voltage for a dry air environment at 20°C and 101.3 kPa is:
≈ 2.1 kV/mm
≈ 4.5 kV/mm
≈ 6.0 kV/mm
≈ 8.0 kV/mm
Explanation - In dry air, corona starts at about 4.5 kV per millimeter of electrode separation.
Correct answer is: ≈ 4.5 kV/mm
Q.7 What is the main advantage of using a DC high voltage test over an AC test?
Lower cost of equipment
Higher frequency of discharge
Reduced risk of partial discharge initiation
Better visualization of flashover
Explanation - DC tests are less likely to trigger PD because the field is constant, whereas AC can oscillate through zero voltage and promote PD.
Correct answer is: Reduced risk of partial discharge initiation
Q.8 In a high voltage surge test, the term 'flyback' refers to:
The reverse voltage after the surge pulse
The delay between the test and the next pulse
The oscillation of the surge generator
The rapid discharge of stored energy in a capacitor
Explanation - Flyback is the negative voltage that appears after the positive surge pulse, caused by the inductance of the surge line.
Correct answer is: The reverse voltage after the surge pulse
Q.9 Which component is essential in a high voltage leak current meter?
A high resistance shunt
A low resistance shunt
An optical sensor
A magnetic core transformer
Explanation - Leakage currents are usually very small; a high resistance shunt allows accurate measurement without loading the circuit.
Correct answer is: A high resistance shunt
Q.10 The term 'dielectric strength' of a material refers to:
Its ability to conduct electricity
The maximum voltage it can withstand per unit length
Its electrical resistance
The amount of charge it can store
Explanation - Dielectric strength is the breakdown voltage per unit thickness (e.g., kV/mm).
Correct answer is: The maximum voltage it can withstand per unit length
Q.11 Which test is primarily used to evaluate the long‑term reliability of high voltage insulating oil?
Partial discharge test
Dielectric strength test
Dissipation factor measurement
High temperature aging test
Explanation - High temperature aging simulates long‑term thermal stress on insulating oil.
Correct answer is: High temperature aging test
Q.12 In a high voltage test, a sudden spike in current is usually an indication of:
A successful test
Insulation failure or flashover
An increase in dielectric strength
Improved test conditions
Explanation - A sharp rise in current indicates breakdown or flashover across the insulation.
Correct answer is: Insulation failure or flashover
Q.13 Which type of high voltage test is most appropriate for checking the insulation of a transformer winding?
Dielectric withstand test
Partial discharge test
Surge test
Corona test
Explanation - The transformer winding insulation must withstand the rated voltage, verified by a dielectric withstand test.
Correct answer is: Dielectric withstand test
Q.14 The rise time of a typical high voltage surge pulse is:
1–2 ms
100–200 µs
10–20 µs
0.1–0.2 µs
Explanation - Surge generators produce very fast pulses with rise times in the sub‑microsecond range.
Correct answer is: 0.1–0.2 µs
Q.15 Which of the following is a key safety precaution during a high voltage dielectric test?
Use a low voltage source
Wear insulated gloves and boots
Avoid grounding the test setup
Keep the test area wet
Explanation - Personal protective equipment protects against accidental shocks.
Correct answer is: Wear insulated gloves and boots
Q.16 The unit of measurement for high voltage leakage current is:
Volts
Amps
Ohms
Watts
Explanation - Leakage current is expressed in amperes (often in micro‑amps).
Correct answer is: Amps
Q.17 What does the term 'flashover' specifically refer to in high voltage testing?
A sudden drop in voltage
A rapid increase in temperature
Electrical discharge over a surface
A decrease in insulation resistance
Explanation - Flashover is the surface conduction of electricity across an insulating material.
Correct answer is: Electrical discharge over a surface
Q.18 The high voltage test voltage must always exceed the rated voltage by at least how many percent?
5 %
10 %
15 %
25 %
Explanation - Standard practice is a 15 % safety margin over rated voltage for dielectric testing.
Correct answer is: 15 %
Q.19 Which instrument is used to measure the electric field during a high voltage corona test?
High voltage probe
Field meter
Current transformer
Voltage divider
Explanation - A field meter measures the local electric field strength during corona onset.
Correct answer is: Field meter
Q.20 In a partial discharge test, what does a high PD count indicate?
Excellent insulation quality
Weak insulation with potential failure
No discharge activity
Low leakage current
Explanation - A high PD count suggests defects in insulation that could lead to failure.
Correct answer is: Weak insulation with potential failure
Q.21 Which of these is a common cause of high voltage corona in outdoor cables?
Water condensation
High humidity
Dust accumulation
All of the above
Explanation - Environmental factors such as moisture, humidity, and dust can trigger corona discharge.
Correct answer is: All of the above
Q.22 The dielectric withstand test typically lasts for how long at a given test voltage?
5 seconds
30 seconds
2 minutes
10 minutes
Explanation - A common test duration is 30 seconds to check for breakdown at the applied voltage.
Correct answer is: 30 seconds
Q.23 Which parameter is measured during a high voltage leakage current test to assess insulation degradation?
Resistance value
Leakage current magnitude
Capacitance value
Inductance value
Explanation - The magnitude of leakage current indicates the degree of insulation deterioration.
Correct answer is: Leakage current magnitude
Q.24 What is the typical voltage rise time for a high voltage pulse in a surge test?
1–2 ms
100–200 µs
10–20 µs
0.5–1.0 µs
Explanation - Surge generators produce very rapid rise times to mimic lightning strikes.
Correct answer is: 0.5–1.0 µs
Q.25 During a dielectric test, if the current does not rise significantly, the insulation is considered:
Acceptable
Poor
Failed
Over‑rated
Explanation - Stable low current indicates the insulation can withstand the test voltage.
Correct answer is: Acceptable
Q.26 Which safety device is commonly used to protect personnel during high voltage testing?
Ground fault circuit interrupter
Residual current device (RCD)
Arc fault circuit interrupter (AFCI)
All of the above
Explanation - Each device provides protection against different fault types in high voltage environments.
Correct answer is: All of the above
Q.27 The term 'dielectric voltage rating' refers to:
The maximum continuous voltage the insulation can handle
The peak voltage the test equipment can produce
The rated operating voltage of the conductor
The voltage at which the test ends
Explanation - Dielectric voltage rating indicates the highest sustained voltage the insulation is designed for.
Correct answer is: The maximum continuous voltage the insulation can handle
Q.28 Which of the following best describes the 'flyback' voltage in a surge test?
The positive surge pulse
The negative pulse following the surge
The baseline DC voltage
The ground potential
Explanation - Flyback is the negative voltage that follows the positive surge pulse due to inductive effects.
Correct answer is: The negative pulse following the surge
Q.29 Which parameter is NOT directly affected by temperature during a dielectric withstand test?
Leakage current
Insulation resistance
Voltage rating
Test duration
Explanation - Voltage rating is specified by the manufacturer; temperature mainly affects leakage current and resistance.
Correct answer is: Voltage rating
Q.30 The dielectric strength of oil is typically measured in:
V/m
V/mm
kV/cm
MV/m
Explanation - Oil dielectric strength is commonly expressed in kilovolts per centimeter.
Correct answer is: kV/cm
Q.31 What is the purpose of a high voltage 'flyback' transformer in surge testing?
To increase the test voltage
To shape the surge pulse
To provide isolation
To measure leakage current
Explanation - Flyback transformers produce controlled fast voltage pulses for surge testing.
Correct answer is: To shape the surge pulse
Q.32 In a partial discharge test, what does a sudden drop in PD count indicate?
Improved insulation
Insulation damage
Instrument failure
No change
Explanation - A drop in PD activity suggests the elimination or reduction of defects.
Correct answer is: Improved insulation
Q.33 Which test is used to evaluate the resistance of high voltage cables to surface tracking?
Dielectric withstand test
Surface tracking test
Partial discharge test
Corona test
Explanation - Surface tracking tests expose the cable to a high voltage and moisture to initiate tracking.
Correct answer is: Surface tracking test
Q.34 The maximum permissible leakage current for a 400 V rated device is typically:
5 µA
50 µA
500 µA
5 mA
Explanation - Low‑voltage devices are limited to very small leakage currents for safety.
Correct answer is: 5 µA
Q.35 Which component is commonly used to attenuate high frequency noise in a high voltage test setup?
Capacitor
Resistor
Inductor
Ferrite bead
Explanation - Ferrite beads suppress high‑frequency noise on cables and wires.
Correct answer is: Ferrite bead
Q.36 A high voltage dielectric test is considered a 'pass' if the leakage current stays below:
1 % of the rated current
5 % of the rated current
10 % of the rated current
20 % of the rated current
Explanation - Most standards allow up to 5 % leakage during the test period.
Correct answer is: 5 % of the rated current
Q.37 Which of the following is a primary factor influencing the dielectric strength of a solid polymer insulation?
Thickness
Temperature
Humidity
All of the above
Explanation - Dielectric strength depends on material thickness, operating temperature, and moisture levels.
Correct answer is: All of the above
Q.38 What is the function of a surge arrestor in high voltage systems?
To block DC current
To limit surge voltage to a safe level
To increase system voltage
To reduce insulation resistance
Explanation - Surge arrestors clamp over‑voltages to protect equipment.
Correct answer is: To limit surge voltage to a safe level
Q.39 The dielectric breakdown of a gas typically occurs at a voltage of:
0.3 kV/mm
3.0 kV/mm
30 kV/mm
300 kV/mm
Explanation - Air breakdown occurs around 3 kV per mm of separation.
Correct answer is: 3.0 kV/mm
Q.40 Which measurement is taken during a high voltage corona test to determine the onset voltage?
Voltage rise
Current increase
Sound level
Temperature rise
Explanation - The corona inception voltage is identified when the voltage is increased until a small current appears.
Correct answer is: Voltage rise
Q.41 In high voltage testing, what does the term 'voltage holding time' refer to?
Time the test voltage is applied
Time the instrument is turned on
Time the insulation remains intact
Time to reach rated voltage
Explanation - It is the duration for which the test voltage is maintained during the dielectric test.
Correct answer is: Time the test voltage is applied
Q.42 Which test would you perform to check for surface tracking on a high voltage cable?
Partial discharge test
Surface tracking test
Dielectric withstand test
Corona test
Explanation - Surface tracking tests the cable's resistance to electrical tracks that can form on the surface.
Correct answer is: Surface tracking test
Q.43 What is the typical test voltage for a high voltage insulation resistance tester rated for up to 30 kV?
1 kV
5 kV
10 kV
30 kV
Explanation - Insulation testers often apply a fraction of their maximum rating (e.g., 1/6 max).
Correct answer is: 5 kV
Q.44 During a dielectric test, a sudden rise in current after the initial stabilization is commonly known as:
Sparkover
Arcing
Flashover
Breakdown
Explanation - A breakdown is a rapid increase in current indicating insulation failure.
Correct answer is: Breakdown
Q.45 Which factor does NOT affect the corona inception voltage?
Electrode shape
Air humidity
Temperature
Wavelength of light
Explanation - Corona inception depends on geometry, humidity, and temperature, not on light wavelength.
Correct answer is: Wavelength of light
Q.46 The standard test for high voltage cable insulation resistance is known as:
IEC 60204
IEC 60068-11
IEC 60255
IEC 60279
Explanation - IEC 60255 covers tests of cable insulation resistance at high voltages.
Correct answer is: IEC 60255
Q.47 Which of the following is a typical duration for a high voltage partial discharge test?
1 second
30 seconds
5 minutes
15 minutes
Explanation - Partial discharge tests usually run for several minutes to collect statistical data.
Correct answer is: 5 minutes
Q.48 In a high voltage test, the 'voltage drop' across the test leads should be:
Zero
Minimal
Significant
Unknown
Explanation - Test leads should have low impedance to avoid affecting the measured voltage.
Correct answer is: Minimal
Q.49 Which parameter is crucial when selecting a high voltage surge tester?
Maximum surge energy
Frequency of the pulse
Rise time of the pulse
All of the above
Explanation - Surge tester performance is defined by energy, frequency, and rise time specifications.
Correct answer is: All of the above
Q.50 The dielectric strength of a high voltage gas‑insulated switchgear is typically measured at what pressure?
0.5 atm
1 atm
1.5 atm
2 atm
Explanation - Standard measurements are performed at atmospheric pressure (1 atm).
Correct answer is: 1 atm
Q.51 Which instrument would you use to detect early signs of insulation failure in a high voltage system?
Voltage divider
Partial discharge detector
Current transformer
Temperature probe
Explanation - Partial discharge detectors identify minute discharges before full breakdown occurs.
Correct answer is: Partial discharge detector
Q.52 A high voltage test apparatus must include a:
High voltage connector
Grounded chassis
Low impedance grounding
All of the above
Explanation - Safety and accurate measurements require proper connectors, grounding, and low impedance paths.
Correct answer is: All of the above
Q.53 In a high voltage dielectric test, which of the following readings indicates a good insulation condition?
Stable low leakage current
High leakage current that rises gradually
No current at all
Sudden current spike
Explanation - Consistent low current over the test period signifies acceptable insulation.
Correct answer is: Stable low leakage current
Q.54 Which of the following is a direct measurement of the insulating material’s ability to resist electrical flow?
Capacitance
Dielectric strength
Leakage current
Voltage rating
Explanation - Leakage current indicates how much current flows through the insulation at a given voltage.
Correct answer is: Leakage current
Q.55 The dielectric withstand test is also known as the:
Insulation resistance test
Dielectric strength test
Breakdown test
Partial discharge test
Explanation - It verifies the ability of insulation to withstand applied voltage without breakdown.
Correct answer is: Dielectric strength test
Q.56 Which safety device is specifically designed to protect against high voltage surge faults?
Surge protector
Ground fault circuit interrupter
Residual current device
Arc fault circuit interrupter
Explanation - Surge protectors clamp over‑voltages to safe levels.
Correct answer is: Surge protector
Q.57 During a high voltage test, if the measured current increases exponentially with time, the insulation is likely:
Degraded
Excellent
Insulated
Unrelated
Explanation - Exponential current growth indicates progressive breakdown or degradation.
Correct answer is: Degraded
Q.58 The test voltage for a 100 kV cable must be at least:
80 kV
90 kV
110 kV
120 kV
Explanation - A 10–15 % safety margin above the rated voltage is standard.
Correct answer is: 110 kV
Q.59 Which of the following is a typical source of high voltage surge in power systems?
Lightning
Motor starting
Cable faults
All of the above
Explanation - Surges can come from external lightning, switching operations, or fault currents.
Correct answer is: All of the above
Q.60 What is the recommended method to measure leakage current in high voltage circuits?
Using a shunt resistor
Using a high voltage probe
Using a voltage divider
Using an oscilloscope
Explanation - A high‐value shunt resistor allows precise current measurement without affecting the circuit.
Correct answer is: Using a shunt resistor
Q.61 Which of the following is a typical test duration for a high voltage surface tracking test?
30 seconds
5 minutes
30 minutes
1 hour
Explanation - Surface tracking tests often run for 30 minutes under high voltage and humidity.
Correct answer is: 30 minutes
Q.62 A high voltage surge tester operates by generating pulses of:
Continuous DC voltage
High frequency AC voltage
Fast rise time voltage spikes
Low frequency AC voltage
Explanation - Surge testers produce short, fast pulses to simulate lightning strikes.
Correct answer is: Fast rise time voltage spikes
Q.63 Which measurement is used to indicate the quality of insulation in high voltage equipment?
Dielectric strength
Capacitance per unit length
Leakage current
Voltage rating
Explanation - Lower leakage current suggests better insulation quality.
Correct answer is: Leakage current
Q.64 The maximum permissible leakage current for a 600 V high voltage switch is typically:
5 µA
50 µA
500 µA
5 mA
Explanation - Low‑voltage safety standards limit leakage current to extremely low values.
Correct answer is: 5 µA
Q.65 Which of the following tests is specifically designed to assess the high voltage insulation of transformers?
Dielectric withstand test
Partial discharge test
Corona test
Surface tracking test
Explanation - Transformers are tested for their ability to withstand applied voltage without breakdown.
Correct answer is: Dielectric withstand test
Q.66 The 'flyback' voltage in a surge test is generally:
Positive
Negative
Zero
Irrelevant
Explanation - Flyback is the negative pulse following the positive surge.
Correct answer is: Negative
Q.67 During a high voltage test, the 'voltage hold time' is primarily to ensure:
The test equipment remains stable
The insulation withstands the test voltage
The test voltage can be increased
The current measurement stabilizes
Explanation - The hold time verifies that the insulation remains intact under the applied voltage.
Correct answer is: The insulation withstands the test voltage
Q.68 Which of the following is NOT a typical type of high voltage test?
Dielectric breakdown test
Partial discharge test
Temperature test
Corona test
Explanation - Temperature tests are not high voltage tests; they are thermal tests.
Correct answer is: Temperature test
Q.69 What is the main purpose of a high voltage insulation resistance tester?
To determine the dielectric strength of a material
To test the insulation resistance between conductors
To measure the capacitance of a cable
To assess the corona inception voltage
Explanation - An insulation resistance tester, often called a megohmmeter, measures the resistance between conductors to evaluate insulation health.
Correct answer is: To test the insulation resistance between conductors
Q.70 What is the typical voltage rise time of a high voltage surge pulse used in lightning simulation?
100 µs
10 µs
0.5 µs
0.1 µs
Explanation - Surge generators produce extremely fast rise times, typically around half a microsecond, to replicate lightning strikes.
Correct answer is: 0.5 µs
Q.71 Which of the following parameters is critical when selecting a high voltage dielectric test apparatus?
Maximum test voltage
Test frequency
Maximum test time
All of the above
Explanation - All three parameters are essential: voltage, frequency, and duration determine the test’s validity.
Correct answer is: All of the above
Q.72 Which type of high voltage test is used to identify small electrical discharges within insulation before full breakdown occurs?
Dielectric breakdown test
Partial discharge test
Corona test
Surface tracking test
Explanation - Partial discharge testing reveals internal defects by detecting micro‑discharges.
Correct answer is: Partial discharge test
Q.73 During a high voltage surface tracking test, the cable is exposed to:
High voltage and dry air
High voltage and high humidity
High frequency AC
Low voltage DC
Explanation - Surface tracking tests involve applying high voltage under humid conditions to encourage tracking paths.
Correct answer is: High voltage and high humidity
Q.74 Which safety equipment should be used when handling high voltage test equipment?
Insulated gloves
Grounded mats
Both A and B
None of the above
Explanation - Insulated gloves and grounded mats protect against electric shock during testing.
Correct answer is: Both A and B
Q.75 A high voltage leakage current meter typically measures currents in what range?
µA to mA
A to kA
nA to µA
mA to A
Explanation - Leakage currents in high voltage systems are often in the micro‑ampere to milli‑ampere range.
Correct answer is: µA to mA
Q.76 What is the primary benefit of performing a dielectric withstand test on high voltage equipment?
To evaluate the mechanical strength
To determine the electrical insulation quality
To measure the temperature rise
To check for magnetic fields
Explanation - Dielectric testing verifies that insulation can handle operating voltages without breakdown.
Correct answer is: To determine the electrical insulation quality
Q.77 Which of the following is a standard specification for high voltage dielectric testing?
Maximum voltage rise time
Test voltage rating
Temperature coefficient
All of the above
Explanation - Standard tests specify voltage, rise time, and temperature limits for reliable results.
Correct answer is: All of the above
Q.78 During a high voltage surge test, the 'flyback' voltage is typically:
Positive
Negative
Zero
Constant
Explanation - Flyback is the negative pulse that follows the positive surge due to inductive effects.
Correct answer is: Negative
Q.79 The dielectric strength of dry air at standard conditions is approximately:
3 kV/mm
6 kV/mm
12 kV/mm
24 kV/mm
Explanation - Air typically breaks down at about 3 kV per millimeter of separation.
Correct answer is: 3 kV/mm
Q.80 Which of the following best describes the purpose of a high voltage corona test?
To detect early signs of insulation failure
To evaluate the maximum operating voltage
To determine the dielectric constant
To measure leakage current
Explanation - Corona testing identifies surface discharges that can indicate impending breakdown.
Correct answer is: To detect early signs of insulation failure
Q.81 Which of the following is a common safety guideline for performing high voltage tests?
Never exceed 1.5× the rated voltage
Always test in dry conditions
Use a test voltage lower than the rated voltage
Perform tests in a shielded enclosure
Explanation - Testing below the rated voltage reduces the risk of accidental breakdown.
Correct answer is: Use a test voltage lower than the rated voltage
Q.82 During a high voltage partial discharge measurement, the PD signal is usually captured by:
A high voltage probe
A current transformer
An optical sensor
All of the above
Explanation - High voltage probes convert the electric field to a measurable signal.
Correct answer is: A high voltage probe
Q.83 Which of the following is a typical criterion for a successful high voltage dielectric test?
No visible spark or arc
No measurable leakage current
No increase in current during the test
All of the above
Explanation - A successful test shows no spark, no current rise, and low leakage.
Correct answer is: All of the above
Q.84 In high voltage testing, what is the primary role of a voltage divider?
To measure high voltages safely
To reduce current for measurement
To convert AC to DC
To step up voltage
Explanation - A voltage divider reduces high voltage levels to safe, measurable ranges.
Correct answer is: To measure high voltages safely
Q.85 A high voltage test instrument must be rated for:
At least the maximum test voltage
At least twice the maximum test voltage
The exact test voltage
Half the maximum test voltage
Explanation - The instrument's rating must meet or exceed the highest voltage to be applied.
Correct answer is: At least the maximum test voltage
Q.86 What is the main objective of a high voltage leakage current test?
To determine dielectric strength
To evaluate insulation degradation
To measure capacitance
To assess magnetic fields
Explanation - Leakage current measurement indicates the health of insulation over time.
Correct answer is: To evaluate insulation degradation
Q.87 Which of the following is a typical result of a successful dielectric test?
A high current spike
A steady low leakage current
No measurable current
An increase in voltage
Explanation - Successful tests show low leakage currents without current spikes.
Correct answer is: A steady low leakage current
Q.88 Which of the following factors influences the dielectric breakdown of an insulating material?
Temperature
Humidity
Material thickness
All of the above
Explanation - Breakdown voltage is affected by temperature, moisture, and physical thickness.
Correct answer is: All of the above
Q.89 The main purpose of a high voltage surge tester is to:
Simulate lightning strikes
Test insulation resistance
Measure leakage current
Evaluate corona inception
Explanation - Surge testers generate high‑speed voltage pulses mimicking natural lightning.
Correct answer is: Simulate lightning strikes
Q.90 During a high voltage test, the voltage is applied for:
A very short time
A predetermined test time
Indefinitely
Only when a fault occurs
Explanation - The test applies a controlled voltage for a specific duration to assess insulation.
Correct answer is: A predetermined test time
Q.91 Which of the following is a typical safety precaution when performing high voltage testing?
Ensure all connections are secure
Wear insulated gloves
Keep the area dry
All of the above
Explanation - Proper safety includes secure connections, PPE, and a dry environment.
Correct answer is: All of the above
Q.92 The typical test voltage for a 3 kV cable dielectric test is:
3 kV
4 kV
5 kV
6 kV
Explanation - A 10–15 % margin above the rated voltage is used, giving 4 kV for a 3 kV cable.
Correct answer is: 4 kV
Q.93 In a partial discharge test, the PD event is typically recorded as:
Voltage spikes
Current spikes
Pulse count
All of the above
Explanation - PD events are quantified by counting pulses over a given period.
Correct answer is: Pulse count
Q.94 Which type of high voltage test is used to check the surface tracking capability of cable insulation?
Dielectric withstand test
Surface tracking test
Partial discharge test
Corona test
Explanation - Surface tracking tests evaluate the insulation's resistance to surface discharge paths.
Correct answer is: Surface tracking test
Q.95 In high voltage testing, a 'voltage rise time' refers to:
Time to reach the peak voltage
Time between two voltage peaks
Time of voltage decay
Time of voltage maintenance
Explanation - Rise time is how quickly the applied voltage reaches its maximum value.
Correct answer is: Time to reach the peak voltage
Q.96 The dielectric strength of a solid polymer is typically expressed in:
kV/mm
V/m
V/cm
All of the above
Explanation - Dielectric strength for polymers is usually given in kilovolts per millimeter.
Correct answer is: kV/mm
Q.97 Which of the following is a typical measurement of a high voltage leakage current meter?
Voltage drop
Current in microamps
Resistance in ohms
Capacitance in farads
Explanation - Leakage current meters measure currents typically in the µA range.
Correct answer is: Current in microamps
Q.98 In a high voltage test, the 'flyback' voltage is caused by:
Capacitance of the test leads
Inductance of the surge line
Resonance in the circuit
None of the above
Explanation - Inductive effects cause a negative flyback after the positive surge.
Correct answer is: Inductance of the surge line
Q.99 What is the typical test voltage used for a 35 kV power line dielectric test?
30 kV
35 kV
40 kV
45 kV
Explanation - A 10–15 % margin above rated voltage gives about 45 kV for a 35 kV line.
Correct answer is: 45 kV
Q.100 Which of the following is a common criterion for a successful partial discharge test?
Zero PD counts
PD counts below a specified limit
PD counts above a specified limit
No measurable PD events
Explanation - Tests accept PD counts that are within a predetermined limit.
Correct answer is: PD counts below a specified limit
Q.101 During a dielectric test, a sudden current increase indicates:
The equipment is operating normally
The insulation is degraded or failed
The test voltage was too low
The test duration was too short
Explanation - A sudden current rise shows breakdown or partial breakdown of the insulation.
Correct answer is: The insulation is degraded or failed
Q.102 The 'dielectric strength' of a material is best defined as:
The maximum voltage the material can handle per unit thickness
The ability of the material to conduct current
The temperature range of operation
The cost of the material
Explanation - Dielectric strength is measured in kV/mm, indicating how much voltage per mm it can withstand.
Correct answer is: The maximum voltage the material can handle per unit thickness
Q.103 In a high voltage test, the term 'flashover' refers to:
A sudden rise in voltage
A sudden rise in current across a surface
A sudden drop in voltage
A sudden drop in current across a surface
Explanation - Flashover is an arc or discharge over an insulating surface when the electric field exceeds a critical level.
Correct answer is: A sudden rise in current across a surface
Q.104 Which test is used to evaluate the high voltage insulation of gas‑insulated switchgear?
Dielectric withstand test
Partial discharge test
Corona test
Surface tracking test
Explanation - Gas‑insulated switchgear is tested for its ability to withstand high voltage without breakdown.
Correct answer is: Dielectric withstand test
Q.105 What is the typical time duration for a high voltage surface tracking test?
30 seconds
5 minutes
30 minutes
1 hour
Explanation - Surface tracking tests often run for 30 minutes under high voltage and humidity conditions.
Correct answer is: 30 minutes
Q.106 Which of the following is the main purpose of a high voltage test apparatus?
To apply a specified voltage for a specific time
To measure resistance of a circuit
To detect magnetic fields
To measure temperature rise
Explanation - The test apparatus is designed to supply controlled high voltage for a set period.
Correct answer is: To apply a specified voltage for a specific time
Q.107 Which of the following is NOT a common parameter measured during a high voltage surge test?
Energy of the surge
Rise time
Peak voltage
Capacitance of the cable
Explanation - Surge tests focus on energy, rise time, and peak voltage; capacitance is unrelated.
Correct answer is: Capacitance of the cable
Q.108 In high voltage testing, a 'dielectric breakdown' is characterized by:
An increase in leakage current
A decrease in leakage current
No change in current
An increase in voltage
Explanation - Dielectric breakdown leads to a sudden jump in current as the insulation fails.
Correct answer is: An increase in leakage current
Q.109 Which safety measure is crucial before applying high voltage to a test circuit?
Check for loose connections
Verify test voltage is within spec
Ensure test leads are properly insulated
All of the above
Explanation - Safety requires secure connections, correct voltage, and insulated leads.
Correct answer is: All of the above
Q.110 What is the typical voltage used in a high voltage test for a 10 kV cable?
10 kV
12 kV
15 kV
20 kV
Explanation - A 15 % safety margin gives roughly 12 kV for a 10 kV rated cable.
Correct answer is: 12 kV
Q.111 The 'partial discharge' phenomenon is primarily observed in:
Solid insulators
Liquid insulators
All types of insulators
None of the above
Explanation - PD can occur in solids, liquids, or gases when there are defects.
Correct answer is: All types of insulators
Q.112 Which of the following is a typical test for high voltage insulation of transformers?
Dielectric withstand test
Corona test
Partial discharge test
All of the above
Explanation - Transformers undergo dielectric tests to confirm insulation integrity.
Correct answer is: Dielectric withstand test
Q.113 A high voltage leakage current test typically measures current in:
Microamperes (µA)
Milliamperes (mA)
Amperes (A)
Nanometers (nm)
Explanation - Leakage currents at high voltage are usually in the µA range.
Correct answer is: Microamperes (µA)
Q.114 In a dielectric test, the maximum acceptable current rise is typically:
10 % of the test current
5 % of the test current
20 % of the test current
50 % of the test current
Explanation - Most standards allow less than a 5 % increase in current during the test.
Correct answer is: 5 % of the test current
Q.115 Which of the following best describes a corona discharge?
A high‑energy spark
A low‑energy surface discharge
An internal dielectric breakdown
A magnetic field effect
Explanation - Corona is a localized, low‑energy discharge that occurs at high electric field gradients.
Correct answer is: A low‑energy surface discharge
Q.116 The typical maximum test voltage for a 15 kV cable dielectric test is:
17 kV
18 kV
20 kV
25 kV
Explanation - A 15 % safety margin above the rated voltage gives ~20 kV for a 15 kV cable.
Correct answer is: 20 kV
Q.117 Which of the following is a key parameter of a high voltage surge tester?
Pulse energy
Pulse duration
Both A and B
Neither A nor B
Explanation - Surge testers are characterized by pulse energy and duration.
Correct answer is: Both A and B
Q.118 A high voltage test typically involves:
Applying a DC voltage and measuring leakage current
Measuring AC current only
Only visual inspection
Temperature measurement only
Explanation - Dielectric tests use DC voltage to evaluate leakage and breakdown.
Correct answer is: Applying a DC voltage and measuring leakage current
Q.119 The typical maximum permissible leakage current for a 400 V rated device is:
5 µA
50 µA
500 µA
5 mA
Explanation - Low‑voltage safety standards limit leakage currents to a few microamperes.
Correct answer is: 5 µA
Q.120 During a high voltage test, which of the following indicates a good insulation condition?
No current rise during the test
Stable low leakage current
No spark or flashover
All of the above
Explanation - Good insulation shows low leakage, no spark, and no current increase.
Correct answer is: All of the above
Q.121 A high voltage 'flyback' voltage is typically:
Positive
Negative
Zero
Not present
Explanation - Flyback is the negative pulse that follows the positive surge due to inductive effects.
Correct answer is: Negative
Q.122 The typical test voltage for a 5 kV cable dielectric test is:
6 kV
7 kV
8 kV
9 kV
Explanation - A 15 % safety margin over the rated voltage yields about 7 kV for a 5 kV cable.
Correct answer is: 7 kV
Q.123 In high voltage testing, a sudden current spike during a dielectric test indicates:
Successful insulation
Partial or full breakdown
Low temperature
High humidity
Explanation - A spike means the insulation has failed, allowing a large current to flow.
Correct answer is: Partial or full breakdown
Q.124 Which of the following is a typical criterion for a successful high voltage surface tracking test?
No visible tracking paths after the test
No increase in leakage current
No flashover
All of the above
Explanation - A successful test shows no tracking, no current rise, and no flashover.
Correct answer is: All of the above
Q.125 Which of the following instruments is used to detect high voltage partial discharges?
Current transformer
High voltage probe
Optical sensor
All of the above
Explanation - PD detectors can use various transducers, including probes, transformers, or optical sensors.
Correct answer is: All of the above
Q.126 What does the dielectric breakdown voltage of a material represent?
The maximum voltage it can handle per unit length
The temperature at which it melts
The cost of production
The resistance to magnetic fields
Explanation - Breakdown voltage is the highest electric field the material can tolerate before failing.
Correct answer is: The maximum voltage it can handle per unit length
Q.127 Which of the following is NOT typically included in a high voltage test procedure?
Setting test voltage
Measuring leakage current
Inspecting for visual defects
Applying high frequency AC
Explanation - High voltage tests usually use DC or low frequency AC, not high frequency AC.
Correct answer is: Applying high frequency AC
Q.128 During a partial discharge test, the PD activity is usually plotted as:
Current versus voltage
Voltage versus time
PD counts versus time
Power versus frequency
Explanation - PD measurements are often plotted as a count rate over time.
Correct answer is: PD counts versus time
Q.129 Which of the following is a key safety consideration when performing a high voltage dielectric test?
Using insulated test leads
Keeping the test area dry
Ensuring proper grounding
All of the above
Explanation - Safety involves insulated leads, a dry environment, and proper grounding.
Correct answer is: All of the above
Q.130 What is the typical voltage used for a 1 kV cable dielectric test?
1 kV
1.1 kV
1.2 kV
1.5 kV
Explanation - A 20 % safety margin over the rated voltage yields about 1.2 kV for a 1 kV cable.
Correct answer is: 1.2 kV
Q.131 In high voltage testing, the term 'voltage hold time' refers to:
Duration the voltage is applied to the test specimen
Time until the test voltage drops
Time the current stabilizes
The duration of the test pulse
Explanation - Voltage hold time is the period the test voltage remains constant during a dielectric test.
Correct answer is: Duration the voltage is applied to the test specimen
Q.132 Which of the following is typically the highest voltage used in a high voltage testing suite?
10 kV
35 kV
110 kV
330 kV
Explanation - High voltage testing can go up to hundreds of kilovolts for specialized equipment.
Correct answer is: 330 kV
Q.133 The dielectric strength of a 20 mm thick epoxy insulation is:
60 kV
80 kV
120 kV
160 kV
Explanation - Typical epoxy dielectric strength is ~6 kV/mm, giving 120 kV for 20 mm.
Correct answer is: 120 kV
Q.134 What does a high voltage test typically measure?
Leakage current
Dielectric strength
Both A and B
None of the above
Explanation - Dielectric tests measure both leakage current and breakdown voltage.
Correct answer is: Both A and B
Q.135 Which of the following is a typical characteristic of a high voltage surge pulse?
Long rise time
Short rise time
Low amplitude
Zero voltage
Explanation - Surge pulses have very short rise times to emulate lightning.
Correct answer is: Short rise time
Q.136 In a dielectric test, the 'dielectric constant' of a material is measured by:
Applying a voltage and measuring current
Using a capacitance meter
Using a voltage divider
Measuring resistance
Explanation - Dielectric constant is derived from the capacitance of a material under a known electric field.
Correct answer is: Using a capacitance meter
Q.137 The main purpose of a high voltage leakage current test is to:
Check for insulation degradation
Measure dielectric constant
Test magnetic fields
Assess temperature rise
Explanation - Leakage current measurement indicates the state of the insulation.
Correct answer is: Check for insulation degradation
Q.138 Which of the following is a typical safety margin used in high voltage testing?
5 %
10 %
15 %
20 %
Explanation - A 15 % safety margin is common for dielectric tests to ensure equipment integrity.
Correct answer is: 15 %
Q.139 A high voltage test is considered successful if:
No spark or flashover occurs
The current remains below the specified limit
The test voltage is applied for the specified duration
All of the above
Explanation - A successful test requires no flashover, low current, and correct test time.
Correct answer is: All of the above
Q.140 What is the typical test voltage for a 75 kV high voltage line dielectric test?
85 kV
90 kV
95 kV
100 kV
Explanation - A 10–15 % safety margin above 75 kV gives approximately 100 kV for testing.
Correct answer is: 100 kV
Q.141 Which of the following is NOT typically measured during a high voltage corona test?
Corona inception voltage
Corona extinction voltage
Corona current
Capacitance of the test setup
Explanation - Corona tests focus on voltage and current, not capacitance.
Correct answer is: Capacitance of the test setup
Q.142 In a dielectric test, the leakage current should remain:
Below a specified threshold
Below the rated current
Below the test voltage
Below the capacitance value
Explanation - The acceptable leakage current is defined by a threshold for the test.
Correct answer is: Below a specified threshold
Q.143 Which of the following best defines a high voltage 'partial discharge' event?
A full‑scale breakdown across the entire insulation
A localized, small‑scale discharge within the insulation
A chemical reaction in the insulator
A magnetic flux change
Explanation - PD is a small discharge that occurs at defects or voids within the insulator.
Correct answer is: A localized, small‑scale discharge within the insulation
Q.144 What is the typical maximum leakage current allowed for a 0.6 kV low‑voltage circuit?
5 µA
50 µA
500 µA
5 mA
Explanation - Low‑voltage safety standards typically restrict leakage to a few microamps.
Correct answer is: 5 µA
Q.145 In high voltage testing, the 'flyback' voltage is:
Positive
Negative
Zero
None of the above
Explanation - Flyback is a negative pulse following the positive surge.
Correct answer is: Negative
Q.146 Which of the following is NOT a typical parameter measured during a high voltage surge test?
Energy of the surge
Rise time
Peak voltage
Capacitance of the test cable
Explanation - Surge tests focus on energy, rise time, and peak voltage; capacitance is not measured.
Correct answer is: Capacitance of the test cable
Q.147 The dielectric strength of a high voltage transformer windings is typically tested by:
Applying a high frequency AC voltage
Applying a DC voltage higher than the rated voltage
Measuring the current draw
Testing the transformer at low temperatures
Explanation - A dielectric withstand test uses DC voltage to evaluate insulation.
Correct answer is: Applying a DC voltage higher than the rated voltage
Q.148 Which safety device is commonly used to protect against high voltage over‑voltage faults?
Surge protector
Ground fault circuit interrupter
Residual current device
Arc fault circuit interrupter
Explanation - Surge protectors clamp over‑voltage transients to safe levels.
Correct answer is: Surge protector
Q.149 The typical test voltage for a 5 kV cable dielectric test is:
5 kV
6 kV
7 kV
8 kV
Explanation - A 10 % safety margin above the rated voltage gives ~6 kV for a 5 kV cable.
Correct answer is: 6 kV
Q.150 Which of the following is a common method for measuring high voltage leakage current?
Using a high resistance shunt
Using a voltage divider
Using a current transformer
All of the above
Explanation - A high resistance shunt allows accurate measurement of small leakage currents.
Correct answer is: Using a high resistance shunt
Q.151 In high voltage testing, a 'dielectric breakdown' is often identified by:
An increase in current
A decrease in voltage
No change in current
A sudden rise in resistance
Explanation - Breakdown results in a large current surge.
Correct answer is: An increase in current
Q.152 Which of the following best describes a high voltage 'corona discharge'?
A high‑energy spark
A low‑energy surface discharge
An internal dielectric breakdown
A magnetic field effect
Explanation - Corona is a localized surface discharge at high electric field gradients.
Correct answer is: A low‑energy surface discharge
Q.153 During a partial discharge test, a low PD count indicates:
Excellent insulation quality
Insufficient test voltage
High leakage current
Low test frequency
Explanation - Low PD counts mean fewer internal defects.
Correct answer is: Excellent insulation quality
Q.154 The dielectric strength of a typical polymer insulator is about:
1 kV/mm
2 kV/mm
3 kV/mm
4 kV/mm
Explanation - Most polymer insulators have dielectric strengths around 3 kV per millimeter.
Correct answer is: 3 kV/mm
Q.155 Which of the following is a common parameter measured during a high voltage surface tracking test?
Voltage applied
Duration of test
Leakage current
All of the above
Explanation - Surface tracking tests monitor voltage, duration, and leakage current.
Correct answer is: All of the above
Q.156 The main advantage of performing a dielectric test is to:
Determine the insulation resistance
Check for magnetic fields
Measure temperature rise
All of the above
Explanation - Dielectric testing evaluates insulation resistance under applied voltage.
Correct answer is: Determine the insulation resistance
Q.157 In high voltage testing, a 'partial discharge' is typically detected using:
A high voltage probe
An oscilloscope
A current transformer
All of the above
Explanation - PD detectors can use probes, oscilloscopes, or current transformers.
Correct answer is: All of the above
Q.158 The typical test voltage for a 100 kV cable is:
110 kV
120 kV
130 kV
140 kV
Explanation - A 30 % safety margin above 100 kV yields 130 kV.
Correct answer is: 130 kV
Q.159 A high voltage surge test simulates:
Switching transients
Lightning strikes
Both A and B
None of the above
Explanation - Surge tests mimic both lightning and switching surges.
Correct answer is: Both A and B
Q.160 In a high voltage test, the term 'breakdown voltage' refers to:
The voltage at which the insulation starts to conduct
The voltage at which the test voltage is applied
The voltage at which the equipment is rated
The maximum voltage the tester can supply
Explanation - Breakdown voltage is the threshold where the insulation fails and current flows.
Correct answer is: The voltage at which the insulation starts to conduct