What is the basic Marx-generator charging arrangement?
A Inductors charged in series
B Capacitors charged in parallel
C Resistors charged together
D Diodes in a bridge
Answer: B. Capacitors charged in parallel. In a Marx generator, stage capacitors are charged in parallel and then connected in series for impulse discharge.
What happens to Marx stages during impulse discharge?
A They remain parallel
B They connect in series
C They open individually
D They become a transformer
Answer: B. They connect in series. Triggered spark gaps connect the charged capacitors in series to produce a high impulse voltage.
What are wave-front and wave-tail resistors used for?
A Shape impulse waveform
B Set grid frequency
C Measure insulation resistance
D Change conductor material
Answer: A. Shape impulse waveform. The impulse circuit resistors control the rise and decay of the generated impulse waveform.
What is the conventional lightning impulse shape?
A 10/350 microseconds
B 50/60 microseconds
C 1.2/50 microseconds
D 250/2500 microseconds
Answer: C. 1.2/50 microseconds. The commonly used standard lightning impulse is described by a 1.2 microsecond front time and 50 microsecond time to half value.
What is a standard switching impulse shape often written as?
A 1.2/50 microseconds
B 250/2500 microseconds
C 10/350 microseconds
D 50/60 microseconds
Answer: B. 250/2500 microseconds. A commonly used standard switching impulse has a 250 microsecond front and a 2500 microsecond time to half value.
What does a cascade test transformer arrangement provide?
A Lower system frequency
B More insulation resistance
C A DC current source
D Higher test voltage
Answer: D. Higher test voltage. Cascade-connected transformer stages add their secondary voltages to generate high AC test voltage.
Why use a resonant transformer for capacitive test objects?
A Eliminate all test current
B Create DC output only
C Avoid grounding
D Lower input power demand
Answer: D. Lower input power demand. At resonance, the source mainly supplies losses in the test circuit rather than the full reactive power of its capacitance.
What circuit is commonly used for high DC test voltage multiplication?
A Wheatstone bridge
B Schering bridge
C Wien bridge
D Cockcroft-Walton circuit
Answer: D. Cockcroft-Walton circuit. A Cockcroft-Walton multiplier uses diode-capacitor stages to generate high DC voltage.
What does a sphere-gap calibration depend on?
A Load power factor only
B Cable length only
C Gap and atmospheric conditions
D Motor speed
Answer: C. Gap and atmospheric conditions. Sphere-gap disruptive voltage depends on electrode geometry, gap spacing, air density and test conditions.
What does a resistive voltage divider suit well?
A DC and impulse measurement
B Only low-frequency current
C Shaft speed measurement
D Thermal imaging
Answer: A. DC and impulse measurement. Resistive dividers can be used for DC and transient measurements when their frequency response and loading are controlled.
What is a capacitive divider commonly used to measure?
A Insulation resistance
B DC motor speed
C AC and impulse voltage
D Hydraulic flow
Answer: C. AC and impulse voltage. Capacitive dividers are often used for AC and impulse voltage measurement with suitable design and compensation.
What does a Schering bridge measure for insulation?
A Rotor resistance and slip
B Capacitance and loss tangent
C Wind speed and power
D Ground current only
Answer: B. Capacitance and loss tangent. A Schering bridge measures capacitance and dielectric loss characteristics such as tan delta.
What does partial-discharge inception voltage mark?
A Complete insulation puncture
B Rated voltage always
C Zero discharge current
D First specified discharge activity
Answer: D. First specified discharge activity. PD inception voltage is the lowest applied voltage at which discharge activity meeting the stated criterion is observed.
What does partial-discharge extinction voltage mark?
A Discharge activity ceases
B Insulation is punctured
C Voltage reaches rated peak
D Test current doubles
Answer: A. Discharge activity ceases. PD extinction voltage is the voltage below which previously observed discharge activity ceases under the test conditions.
What is apparent charge in a PD test?
A Total insulation capacitance
B Equivalent measured charge transfer
C Peak test voltage
D Conductor surface area
Answer: B. Equivalent measured charge transfer. Apparent charge is the charge that would produce the measured detector response at the test object terminals.
What does a coupling capacitor do in a PD circuit?
A Raises test voltage
B Replaces the test object
C Couples discharge pulses to detector
D Sets grounding resistance
Answer: C. Couples discharge pulses to detector. A coupling capacitor provides a path for high-frequency PD pulses to the measuring circuit while blocking the test voltage appropriately.
What can surface contamination cause on an insulator?
A Leakage and flashover risk
B Higher dielectric strength
C Lower field stress
D Zero surface current
Answer: A. Leakage and flashover risk. Moisture and contamination can create surface leakage current, heating and eventual flashover.
What does a grading ring reduce on an insulator?
A System frequency
B Line current
C End-field concentration
D Creepage distance
Answer: C. End-field concentration. A grading ring redistributes electric field near the energized end and reduces local stress concentration.
Why are bundled conductors used at high voltage?
A Reduce surface electric stress
B Increase corona always
C Shorten insulators
D Remove line inductance
Answer: A. Reduce surface electric stress. Bundling increases effective conductor radius and lowers surface electric-field stress, which can reduce corona effects.
What does corona often produce around conductors?
A Higher insulation resistance
B Noise and radio interference
C Lower conductor temperature
D Zero power loss
Answer: B. Noise and radio interference. Corona can create audible noise, radio interference, ozone and power loss, especially above its onset level.
What is an impulse-voltage test used to assess?
A Steady-state motor torque
B Battery capacity
C Transient insulation withstand
D Conductor ampacity
Answer: C. Transient insulation withstand. Impulse testing checks whether insulation can withstand standardized transient overvoltage waveforms.
What do atmospheric corrections account for in an air gap?
A Conductor resistance
B Battery state of charge
C Transformer oil viscosity
D Air density effects
Answer: D. Air density effects. Air-gap discharge strength depends on air density, so pressure, temperature and humidity corrections may be needed.
What is a common cause of switching overvoltage?
A Normal load current
B Solar-cell mismatch
C Battery discharge
D Circuit-breaker operation
Answer: D. Circuit-breaker operation. Switching operations can initiate transient overvoltages through line energization, interruption or restrike phenomena.
What is lightning protection coordination based on?
A Protective level below withstand
B Protective level above withstand
C Equal conductor resistance
D Maximum load current
Answer: A. Protective level below withstand. The arrester protective level should be coordinated below the equipment insulation withstand level with appropriate margins.
What does an electrostatic voltmeter sense?
A Electric-field force
B Magnetic torque only
C Thermal expansion
D Chemical potential
Answer: A. Electric-field force. An electrostatic voltmeter uses electrostatic force between charged electrodes to indicate voltage.