100 Important MCQs On Current Transformers For Job Seekers
Job seekers, boost your interview readiness! Immerse yourself in 100 important MCQs on Current Transformers, designed to enhance your understanding and confidence.
What is the primary function of a current transformer (CT) in an electrical system?
A. Voltage regulation
B. Current amplification
C. Power factor correction
D. Measuring and monitoring current
Answer: D
Explanation: Current transformers are specifically designed for accurate measurement and monitoring of electrical current in a circuit.
What type of current does a current transformer typically measure?
A. Alternating current (AC)
B. Direct current (DC)
C. Pulsating current
D. Residual current
Answer: A
Explanation: Current transformers are predominantly used for measuring alternating current.
In which part of the power system are current transformers commonly installed?
A. Primary distribution
B. Secondary distribution
C. Generation
D. Transmission
Answer: D
Explanation: Current transformers are often installed in the transmission system to measure high currents and provide accurate readings for protective relaying.
What is the typical current ratio of a current transformer?
A. 1:1
B. 10:1
C. 100:1
D. 1000:1
Answer: C
Explanation: Current transformers are designed with specific ratios to step down high currents to levels suitable for measurement.
What is the purpose of the secondary winding in a current transformer?
A. To step up current
B. To provide power
C. To step down current
D. To regulate voltage
Answer: C
Explanation: The secondary winding of a current transformer reduces the current to a manageable level for measurement and instrumentation.
What is the consequence of short-circuiting the secondary winding of a current transformer?
A. Increased voltage
B. Decreased current
C. Saturation of the core
D. Improved accuracy
Answer: C
Explanation: Short-circuiting the secondary winding can lead to core saturation, affecting the accuracy of the current transformer.
Which parameter is critical for the accuracy of a current transformer?
A. Resistance
B. Inductance
C. Turns ratio
D. Capacitance
Answer: C
Explanation: The turns ratio between the primary and secondary windings is crucial for the accuracy of current transformers.
What is the typical burden in a current transformer specification?
A. Voltage
B. Resistance
C. Impedance
D. Power factor
Answer: B
Explanation: Burden in a current transformer specification refers to the maximum permissible load resistance connected to its secondary winding.
What role do current transformers play in protective relaying systems?
A. Voltage regulation
B. Current amplification
C. Measuring fault currents
D. Controlling power factor
Answer: C
Explanation: Current transformers are integral in protective relaying systems, accurately measuring fault currents for proper relay operation.
What material is commonly used for the core of a current transformer?
A. Copper
B. Aluminum
C. Silicon steel
D. Brass
Answer: C
Explanation: Silicon steel is a common core material in current transformers due to its magnetic properties and low core loss.
How does a current transformer contribute to the safety of electrical systems?
A. By increasing voltage levels
B. By providing power factor correction
C. By isolating the measuring instruments from high currents
D. By regulating current flow
Answer: C
Explanation: A current transformer isolates measuring instruments from high currents, ensuring the safety of the equipment and personnel involved in the measurement process. It steps down the current to manageable levels for accurate and safe measurements.
In what scenarios might a current transformer exhibit saturation, and how does it impact accuracy?
A. Saturation occurs in low current conditions, improving accuracy.
B. Saturation occurs in high current conditions, degrading accuracy.
C. Saturation has no impact on accuracy.
D. Saturation only occurs during short circuits.
Answer: B
Explanation: Saturation in a current transformer happens when it experiences high current levels, leading to distortion in the measurement. This distortion can result in inaccurate readings and affect the overall performance of the transformer.
What role does the turns ratio play in determining the accuracy of a current transformer?
A. It influences the size of the transformer.
B. It affects the saturation of the core.
C. It determines the voltage regulation.
D. It establishes the relationship between primary and secondary currents.
Answer: D
Explanation: The turns ratio defines the relationship between the primary and secondary currents in a current transformer. It directly influences the accuracy of the transformer, as it determines how much the current is stepped down for measurement purposes.
Why is the burden specification important when selecting a current transformer for a specific application?
A. It affects the physical size of the transformer.
B. It determines the primary current rating.
C. It defines the maximum permissible load resistance on the secondary side.
D. It regulates the voltage output.
Answer: C
Explanation: The burden specification indicates the maximum allowable load resistance connected to the secondary winding. Understanding this parameter is crucial to ensure the accurate performance of the current transformer under specific application conditions.
How do current transformers contribute to the efficiency of power monitoring systems?
A. By reducing power consumption
B. By providing real-time voltage regulation
C. By accurately measuring current for power calculation
D. By increasing power factor
Answer: C
Explanation: Current transformers play a pivotal role in power monitoring by precisely measuring current, enabling accurate power calculations. This data is essential for monitoring energy consumption and ensuring the efficient operation of electrical systems.
What challenges may arise from using an incorrectly sized current transformer in a system?
A. Overloading the transformer
B. Decreasing the risk of saturation
C. Improving measurement accuracy
D. Reducing the burden on the secondary side
Answer: A
Explanation: Using an incorrectly sized current transformer can lead to overloading, causing the transformer to operate beyond its specified capacity. This can result in inaccurate measurements, increased heat generation, and potential damage to the transformer.
How do current transformers assist in relay protection schemes?
A. By amplifying fault currents
B. By converting current to voltage
C. By accurately measuring fault currents
D. By regulating the frequency of the current signal
Answer: C
Explanation: Current transformers accurately measure fault currents, providing crucial information for protective relay systems. This ensures prompt and precise responses to faults, enhancing the overall reliability and effectiveness of the protective scheme.
What is the significance of the core material in a current transformer?
A. It determines the physical size of the transformer.
B. It affects the insulation properties.
C. It influences the transformer’s efficiency.
D. It defines the magnetic characteristics of the transformer.
Answer: D
Explanation: The core material in a current transformer is crucial as it defines the magnetic properties of the transformer. Common materials include silicon steel, which provides the required magnetic characteristics for accurate current measurement.
In which scenarios might a current transformer experience accuracy issues, and how can these be mitigated?
A. During low-current conditions; using a higher turns ratio.
B. During high-current conditions; increasing the burden.
C. During low-voltage conditions; reducing the turns ratio.
D. During high-voltage conditions; increasing the secondary resistance.
Answer: B
Explanation: Accuracy issues in a current transformer during high-current conditions can be mitigated by appropriately increasing the burden, ensuring that the secondary winding remains within its specified limits.
What is the purpose of a knee point voltage in a current transformer, and how does it relate to saturation?
A. It defines the transformer’s maximum voltage; it is unrelated to saturation.
B. It indicates the voltage level at which saturation begins; higher knee point voltage improves saturation resistance.
C. It determines the transformer’s minimum voltage; lower knee point voltage improves saturation resistance.
D. It regulates the voltage output; saturation does not impact knee point voltage.
Answer: B
Explanation: The knee point voltage in a current transformer indicates the level at which saturation begins. A higher knee point voltage is desirable as it improves the transformer’s ability to resist saturation, ensuring accurate measurements even under high-current conditions.
The primary purpose of a Current Transformer (CT) is to:
A. Increase the current flowing in a circuit
B. Reduce the voltage level in a circuit
C. Measure high currents safely and accurately
D. Isolate sensitive electronic equipment from ground
Answer: C
Explanation: CTs step down large currents to a safer, measurable level while maintaining the original current waveform. They are crucial for measuring high currents without needing large, expensive ammeters.
The core of a CT is typically made of:
A. Copper wire for high conductivity
B. Iron laminations for efficient magnetic coupling
C. Aluminum foil for lightweight construction
D. Plastic for insulation and mechanical strength
Answer: B
Explanation: Laminated steel cores provide low reluctance for magnetic flux, minimizing energy losses and ensuring accurate current transformation.
In a CT, the primary winding:
A. Has many turns and carries the high current to be measured
B. Has few turns and is connected to the measuring instrument
C. Is made of thicker wire to handle high currents
D. Is optional and not always present
Answer: A
Explanation: The primary winding carries the high current we want to measure and has fewer turns compared to the secondary winding.
The secondary winding of a CT:
A. Has many turns and induces a low-voltage replica of the primary current
B. Carries the high current safely due to its smaller size
C. Is connected directly to the power source
D. Requires no connection and operates wirelessly
Answer: A
Explanation: The secondary winding has more turns than the primary, stepping down the induced voltage while proportionally maintaining the current waveform. It connects to the measuring instrument.
An open circuit in the secondary winding of a CT can lead to:
A. Increased accuracy of the measurement
B. No current flow in the primary winding
C. High voltage and potential overheating
D. Improved safety for personnel
Answer: C
Explanation: An open secondary creates a rapidly changing magnetic field in the core, inducing high voltage and possible overheating, posing a safety hazard.
The ratio error in a CT is caused by:
A. Leakage flux escaping the core
B. Magnetizing current in the primary winding
C. Both leakage flux and magnetizing current
D. Incorrectly rated secondary winding
Answer: C
Explanation: Leakage flux and magnetizing current contribute to the ratio error, leading to slight discrepancies between the primary and secondary currents.
To minimize ratio error in a CT, it’s important to:
A. Use thicker wire for the secondary winding
B. Operate the CT close to its rated current
C. Increase the number of turns in the primary winding
D. Use air instead of iron for the core material
Answer: B
Explanation: Operating the CT closer to its rated current minimizes the impact of leakage flux and magnetizing current on the ratio error.
A type of CT designed for measuring DC currents is known as a:
A. Rogowski coil
B. Hall effect CT
C. Split-core CT
D. Window type CT
Answer: A
Explanation: Rogowski coils use a toroidal design and utilize the Hall effect to measure DC currents without requiring a physical connection to the conductor.
Which safety precaution is essential when working with CTs?
A. Touching the secondary terminals is always safe
B. Never open the secondary circuit while current is flowing
C. Always use insulated tools and PPE
D. All of the above
Answer: D
Explanation: Never open the secondary circuit to avoid high voltage and potential sparking. Use insulated tools and PPE for additional safety.
What is the main advantage of using CTs compared to direct connection ammeters for high currents?
A. Lower cost and simpler design
B. Smaller size and lighter weight
C. Isolation from high voltage circuits
D. All of the above
Answer: D
Explanation: CTs offer a combination of cost-effectiveness, compact size, and isolation from high voltage, making them ideal for safe and accurate measurement of high currents.
What is the fundamental principle behind the operation of a Current Transformer (CT)?
A. Electromagnetic induction and Faraday’s Law of Induction
B. Ohm’s Law and resistance drop across the winding
C. Hall effect and the magnetic field around a conductor
D. Voltage divider principle with multiple windings
Answer: A
Explanation: The CT operates based on electromagnetic induction where the primary current creates a magnetic field that induces a proportional current in the secondary winding.
How does the turns ratio of a CT affect the output current?
A. It has no impact on the output current, only voltage.
B. It directly multiplies the output current by the ratio value.
C. It inversely divides the output current by the ratio value.
D. It determines the phase shift between the primary and secondary currents.
Answer: C
Explanation: The turns ratio acts as a scaling factor, inversely transforming the high primary current to a lower measurable secondary current.
What is the significance of the knee point in the CT saturation curve?
A. It indicates the maximum safe operating current for the CT.
B. It marks the transition point where accuracy starts to degrade due to core saturation.
C. It defines the optimal current level for achieving the highest sensitivity.
D. It represents the point where the core material loses its magnetic properties.
Answer: B
Explanation: Beyond the knee point, core saturation leads to a rapid rise in magnetizing current and significant ratio error, compromising measurement accuracy.
Which type of CT is often used for measuring currents in non-standard or awkward shapes?
A. Wound type CT with multiple primary turns
B. Window type CT with a fixed aperture
C. Split-core CT with separable halves for clamping
D. Rogowski coil with toroidal design
Answer: C
Explanation: Split-core CTs offer flexibility by allowing clamping around existing conductors without interrupting the circuit, making them suitable for non-standard shapes.
How can burden impedance in the secondary circuit affect CT performance?
A. It has no impact as long as the secondary is closed.
B. High burden reduces accuracy by decreasing the induced current.
C. Low burden increases ratio error due to magnetizing current dominance.
D. Both high and low burden can lead to performance issues.
Answer: D
Explanation: Both high and low burden impedance can cause issues. High burden reduces secondary current and accuracy, while low burden increases magnetizing current and ratio error. Matching the burden to the CT rating is crucial.
What are some methods for reducing harmonics in the secondary current of a CT?
A. Increasing the number of turns in the primary winding
B. Using thicker wires for both primary and secondary windings
C. Selecting a CT with a higher rated current capacity
D. Adding filters or harmonic traps to the secondary circuit
Answer: D
Explanation: Filters or harmonic traps specifically target and mitigate unwanted harmonic components in the secondary current, improving measurement accuracy.
What are the key differences between current transformers (CTs) and potential transformers (PTs)?
A. CTs measure current while PTs measure voltage.
B. CTs have more turns in the primary than the secondary, while PTs have the opposite.
C. CTs isolate from high voltage while PTs isolate from high current.
D. Both A and B are correct.
Answer: D
Explanation: Both statements are true. CTs step down high currents, while PTs step down high voltages. Additionally, CTs provide galvanic isolation from high voltage, while PTs isolate from high current.
What are the potential health and safety risks associated with working with CTs?
A. Exposure to high voltage and potential shock hazards
B. Inhalation of harmful metal dust from the core material
C. Risk of cuts and abrasions from sharp edges
D. All of the above
Answer: D
Explanation: All options pose potential risks. Always follow safety protocols, including using PPE, avoiding open secondary circuits, and being aware of voltage levels.
What are some emerging trends and innovations in the field of Current Transformers?
A. Development of high-accuracy miniaturized CTs for embedded applications
B. Integration of digital signal processing and communication capabilities
C. Exploration of alternative core materials with improved saturation characteristics
D. All of the above
Answer: D
Explanation: These trends are all actively pursueD. Miniaturization, digital integration, and advanced core materials represent promising advancements for CT technology.
How does the frequency of the measured current impact the performance of a CT?
A. It has no significant effect on accuracy within the rated frequency range.
B. Higher frequencies cause increased core losses and potential overheating.
C. Lower frequencies lead to higher magnetizing current and reduced sensitivity.
D. Both higher and lower frequencies can cause performance issues.
Answer: D
Explanation: Both high and low frequencies can affect accuracy. High frequencies induce eddy currents and increase core losses, while low frequencies lead to a higher proportion of magnetizing current, impacting the ratio error.
What is the purpose of using a burden resistor in the secondary circuit of a CT?
A. To limit the short-circuit current in case of a fault
B. To provide a defined load impedance for accurate current measurement
C. To dissipate excess heat generated by the CT core
D. To isolate the measuring instrument from ground potential
Answer: B
Explanation: The burden resistor defines the load impedance seen by the secondary winding, ensuring accurate current transformation and maintaining the CT’s operating characteristics.
What is the principle behind Rogowski coils, a type of non-invasive CT?
A. They utilize Hall effect sensors to measure magnetic field strength.
B. They employ a toroidal design to measure the rate of change of magnetic flux.
C. They rely on transformer action with multiple primary and secondary windings.
D. They require physical contact with the conductor for accurate measurement.
Answer: B
Explanation: Rogowski coils measure the rate of change of magnetic field around the conductor enclosed by the toroid, offering non-invasive current measurement without needing direct contact.
How can ground faults in a system affect the performance of a CT?
A. They have no impact as long as the CT is properly grounded.
B. They can induce circulating currents that distort the measured current.
C. They can damage the insulation and compromise the safety of the CT.
D. Both B and C.
Answer: D
Explanation: Ground faults can create unwanted circulating currents in the CT secondary, distorting the actual measurement and potentially posing safety risks due to insulation breakdown.
Explain the concept of “leakage flux” in CTs and its impact on measurement accuracy.
A. Leakage flux is a negligible phenomenon in well-designed CTs, having no impact on accuracy.
B. Leakage flux represents a small portion of the magnetic flux that escapes the core, causing minor ratio errors.
C. Leakage flux significantly distorts the magnetic field in the core, leading to substantial inaccuracies.
D. Leakage flux only occurs in Rogowski coils due to their toroidal design.
Answer: B
Explanation: Leakage flux is unavoidable and contributes to ratio errors, especially at lower currents. Careful design and material selection minimize its impact.
How can digital signal processing (DSP) be integrated into CTs to enhance their functionality?
A. DSP allows for direct conversion of secondary current to digital signals, eliminating the need for external analog-to-digital converters (ADCs).
B. DSP enables advanced filtering techniques to remove harmonics and noise from the measured current, improving signal quality.
C. DSP facilitates communication capabilities, allowing CTs to transmit data directly to monitoring systems via networks.
D. All of the above.
Answer: D
Explanation: Integrating DSP offers various benefits, including signal conversion, filtering, communication, and even on-board diagnostics for improved functionality and data accessibility.
What is the primary function of a current transformer (CT)?
A. Measure voltage
B. Measure current
C. Control frequency
D. Control power factor
Answer: B
Explanation: Current transformers are designed to measure current in electrical circuits, providing a reduced current proportional to the actual current.
In which type of electrical equipment are current transformers commonly used?
A. Refrigerators
B. Microwave ovens
C. Power distribution systems
D. Electric fans
Answer: C
Explanation: Current transformers are extensively used in power distribution systems to measure the current flowing through the circuits.
What is the purpose of reducing the current in a current transformer?
A. Increase accuracy
B. Decrease accuracy
C. Enhance voltage measurement
D. Reduce overall power consumption
Answer: A
Explanation: Reducing the current in a current transformer helps to improve measurement accuracy and ensures safe readings.
What is the typical secondary current rating of a standard current transformer?
A. 5 A
B. 10 A
C. 20 A
D. 50 A
Answer: A
Explanation: Standard current transformers often have a secondary current rating of 5 Amperes.
Where is the secondary of a current transformer connected?
A. In parallel with the primary
B. In series with the primary
C. To a separate circuit
D. Grounded to the earth
Answer: C
Explanation: The secondary of a current transformer is connected to a separate circuit for measurement and protection purposes.
What is the typical transformation ratio of a current transformer?
A. 1:1
B. 10:1
C. 100:1
D. 1000:1
Answer: C
Explanation: Current transformers commonly have high transformation ratios, such as 100:1, to reduce high primary currents to manageable secondary currents.
In a current transformer, what is the consequence of an open secondary circuit?
A. Increased accuracy
B. Decreased accuracy
C. No impact on accuracy
D. Tripping of the primary circuit
Answer: B
Explanation: An open secondary circuit in a current transformer results in decreased accuracy, as there is no load on the secondary winding.
Which parameter determines the accuracy class of a current transformer?
A. Primary voltage
B. Secondary voltage
C. Transformation ratio
D. Burden and accuracy requirements
Answer: D
Explanation: The accuracy class of a current transformer is determined by factors like burden (load) and specified accuracy requirements.
What is the purpose of the magnetic core in a current transformer?
A. Increase resistance
B. Decrease transformation ratio
C. Provide mechanical support
D. Enhance magnetic induction
Answer: D
Explanation: The magnetic core in a current transformer is designed to enhance magnetic induction and improve the overall performance of the transformer.
What safety feature do current transformers provide in electrical systems?
A. Overvoltage protection
B. Overcurrent protection
C. Short circuit protection
D. Earth fault protection
Answer: B
Explanation: Current transformers play a crucial role in providing overcurrent protection by accurately measuring the current flow in electrical systems.
What is the primary purpose of the secondary winding in a current transformer?
A. To induce voltage
B. To measure current
C. To control frequency
D. To regulate power factor
Answer: A
Explanation: The secondary winding in a current transformer is used to induce a voltage proportional to the current in the primary winding.
What type of fault is current transformers primarily used to detect?
A. Voltage sag
B. Overfrequency
C. Overcurrent
D. Phase imbalance
Answer: C
Explanation: Current transformers are crucial in detecting overcurrent conditions in electrical systems.
In which unit is the accuracy class of a current transformer typically expressed?
A. Percentage
B. Hertz
C. Amperes
D. Ohms
Answer: A
Explanation: The accuracy class of a current transformer is usually expressed as a percentage of the rated current.
What happens if the burden connected to the secondary of a current transformer exceeds its limit?
A. Increased accuracy
B. Decreased accuracy
C. No impact on accuracy
D. Tripping of the primary circuit
Answer: B
Explanation: Exceeding the burden limit can result in decreased accuracy due to higher voltage drops in the secondary winding.
What is the purpose of the core in a current transformer being made from laminated sheets?
A. Increase mechanical strength
B. Decrease magnetic flux
C. Reduce eddy current losses
D. Enhance heat dissipation
Answer: C
Explanation: Laminated cores in current transformers help reduce eddy current losses, improving overall efficiency.
What is the primary function of the primary winding in a current transformer?
A. Induce voltage
B. Measure current
C. Control frequency
D. Regulate power factor
Answer: B
Explanation: The primary winding in a current transformer is responsible for allowing the flow of current to be measured.
What is the typical output of the secondary winding of a current transformer?
A. Voltage
B. Current
C. Frequency
D. Power factor
Answer: A
Explanation: The secondary winding of a current transformer produces a voltage proportional to the current in the primary winding.
In a current transformer, what is the role of the burden?
A. Increase voltage
B. Decrease voltage
C. Limit current
D. Enhance magnetic induction
Answer: C
Explanation: The burden in a current transformer limits the current flowing through the secondary winding.
What is the significance of the accuracy class when specifying a current transformer?
A. Determines physical size
B. Determines voltage rating
C. Defines accuracy requirements
D. Specifies magnetic core material
Answer: C
Explanation: The accuracy class of a current transformer defines the accuracy requirements based on the intended application.
What happens if a current transformer is operated with an open-circuited secondary?
A. Decreased accuracy
B. Increased accuracy
C. No impact on accuracy
D. Tripping of the primary circuit
Answer: A
Explanation: Operating a current transformer with an open-circuited secondary can result in decreased accuracy due to lack of load.
What is the typical frequency range for which current transformers are designed to operate?
A. 50 Hz
B. 60 Hz
C. 50/60 Hz
D. Variable frequency
Answer: C
Explanation: Current transformers are commonly designed to operate within the standard power system frequency range of 50/60 Hz.
In what application are protection current transformers primarily used?
A. Energy measurement
B. Power factor correction
C. Motor control circuits
D. Relay and protection schemes
Answer: D
Explanation: Protection current transformers are specifically employed in relay and protection schemes to detect and isolate faults.
What is the purpose of the secondary winding having multiple taps in some current transformers?
A. Control voltage
B. Adjust transformation ratio
C. Limit current
D. Enhance magnetic induction
Answer: B
Explanation: Multiple taps on the secondary winding allow for adjusting the transformation ratio to meet specific requirements.
How does the accuracy of a current transformer vary with the magnitude of the primary current?
A. Increases with current
B. Decreases with current
C. Remains constant
D. Depends on the frequency
Answer: B
Explanation: The accuracy of a current transformer often decreases at lower current magnitudes and increases at higher currents.
What is the primary advantage of using a toroidal (ring-type) current transformer?
A. Easy installation
B. High accuracy
C. Variable transformation ratio
D. Low magnetic leakage
Answer: D
Explanation: Toroidal current transformers offer low magnetic leakage, making them suitable for applications with minimal external magnetic interference.
What happens if a current transformer is operated with a short-circuited secondary?
A. Increased accuracy
B. Decreased accuracy
C. No impact on accuracy
D. Tripping of the primary circuit
Answer: B
Explanation: Operating a current transformer with a short-circuited secondary can result in decreased accuracy due to excessive current flow.
What parameter does the transformation ratio of a current transformer express?
A. Secondary voltage to primary current
B. Primary current to secondary voltage
C. Secondary current to primary current
D. Primary voltage to secondary current
Answer: C
Explanation: The transformation ratio of a current transformer expresses the ratio of secondary current to primary current.
What type of core material is commonly used in current transformers to minimize hysteresis losses?
A. Iron
B. Copper
C. Aluminum
D. Silicon steel
Answer: D
Explanation: Silicon steel is often used as the core material in current transformers to reduce hysteresis losses.
In a protection current transformer, what is the significance of the saturation point?
A. Limits accuracy
B. Enhances accuracy
C. Causes malfunction
D. Provides overload protection
Answer: D
Explanation: The saturation point in a protection current transformer helps provide overload protection by limiting the magnetic flux.
What role does the burden resistor play in the secondary circuit of a current transformer?
A. Increases voltage
B. Decreases voltage
C. Limits current
D. Enhances magnetic induction
Answer: C
Explanation: The burden resistor in the secondary circuit of a current transformer is used to limit the current flowing through the secondary winding.
What is the primary application of a wound primary current transformer?
A. Voltage measurement
B. High-voltage protection
C. Frequency control
D. Current measurement in low-voltage circuits
Answer: D
Explanation: Wound primary current transformers are commonly used for accurate current measurement in low-voltage circuits.
How does the accuracy of a current transformer typically change with load (burden)?
A. Increases with load
B. Decreases with load
C. Remains constant
D. Depends on the primary voltage
Answer: B
Explanation: The accuracy of a current transformer generally decreases as the load (burden) on the secondary circuit increases.
What is the purpose of a current transformer core having a circular cross-section?
A. Simplify winding
B. Enhance magnetic induction
C. Reduce eddy current losses
D. Accommodate multiple taps
Answer: C.
Explanation: A circular core cross-section helps reduce eddy current losses in the current transformer.
In which scenario is a bar-type current transformer commonly used?
A. Low-voltage circuits
B. High-voltage circuits
C. Medium-voltage circuits
D. Variable frequency circuits
Answer: B
Explanation: Bar-type current transformers are often used in high-voltage circuits for accurate current measurement.
What safety feature is associated with the secondary of a current transformer?
A. Overvoltage protection
B. Overcurrent protection
C. Short circuit protection
D. Earth fault protection
Answer: C
Explanation: The secondary winding of a current transformer provides short circuit protection in the event of a fault.
What is the primary advantage of using a split-core current transformer?
A. Easier installation
B. Higher accuracy
C. Variable transformation ratio
D. Lower magnetic leakage
Answer: A
Explanation: Split-core current transformers offer the advantage of easier installation without the need to disconnect the primary conductor.
What factor does the turns ratio of a current transformer represent?
A. Primary turns to secondary turns
B. Secondary turns to primary turns
C. Primary current to secondary current
D. Secondary current to primary current
Answer: A
Explanation: The turns ratio of a current transformer represents the ratio of primary turns to secondary turns.
Which characteristic is crucial for the accuracy of a current transformer at high frequencies?
A. Core material
B. Turns ratio
C. Burden resistance
D. Primary current magnitude
Answer: A
Explanation: The core material is crucial for the accuracy of a current transformer at high frequencies.
In a protection scheme, what does it mean if a current transformer is described as “saturable”?
A. Reduced accuracy
B. Enhanced accuracy
C. Provides overload protection
D. Impedes magnetic flux
Answer: C
Explanation: A saturable current transformer provides overload protection by reaching saturation and limiting the magnetic flux.
What is the primary function of the secondary winding in a current transformer with multiple taps?
A. To induce voltage
B. To measure current
C. To control frequency
D. To adjust transformation ratio
Answer: D
Explanation: The secondary winding with multiple taps allows for adjusting the transformation ratio to meet specific requirements.
What is the significance of the knee point voltage in a protection current transformer?
A. Defines accuracy
B. Indicates saturation point
C. Determines burden resistance
D. Specifies transformation ratio
Answer: B.
Explanation: The knee point voltage in a protection current transformer indicates the point where saturation begins, crucial for accurate protection.
What is the primary function of a window-type current transformer?
A. Enhance accuracy
B. Facilitate easy installation
C. Measure current in specific conductors
D. Provide variable transformation ratio
Answer: C
Explanation: Window-type current transformers are designed to measure current in specific conductors without disconnecting them.
How does the accuracy of a current transformer vary with the load (burden) resistance?
A. Increases with load resistance
B. Decreases with load resistance
C. Remains constant
D. Depends on primary voltage
Answer: A
Explanation: The accuracy of a current transformer generally increases with higher load (burden) resistance.
What is the primary purpose of the core saturation in a current transformer?
A. Enhance accuracy
B. Limit secondary current
C. Improve transformation ratio
D. Provide overload protection
Answer: D
Explanation: Core saturation in a current transformer provides overload protection by limiting the magnetic flux.
Which factor is critical for the accurate operation of a current transformer in low-voltage circuits?
A. Core material
B. Turns ratio
C. Burden resistance
D. Primary current magnitude
Answer: A
Explanation: The core material is critical for the accurate operation of a current transformer, especially in low-voltage circuits.
What is the primary role of the secondary winding in a current transformer with a variable transformation ratio?
A. To induce voltage
B. To measure current
C. To control frequency
D. To adjust transformation ratio
Answer: D
Explanation: The secondary winding with a variable transformation ratio allows for adjusting the transformation ratio as needed.
What is the purpose of grounding the secondary of a current transformer?
A. Increase accuracy
B. Decrease accuracy
C. Improve safety
D. Enhance voltage measurement
Answer: C
Explanation: Grounding the secondary of a current transformer improves safety by providing a reference point and reducing the risk of shock.
What is the consequence of using an improper burden in a current transformer?
A. Increased accuracy
B. Decreased accuracy
C. No impact on accuracy
D. Tripping of the primary circuit
Answer: B
Explanation: Using an improper burden in a current transformer can lead to decreased accuracy due to voltage drop and other factors.
What is the primary factor influencing the accuracy class of a current transformer?
A. Primary voltage
B. Secondary voltage
C. Transformation ratio
D. Burden and accuracy requirements
Answer: D
Explanation: The accuracy class of a current transformer is determined by factors like burden (load) and specified accuracy requirements.
In a protection current transformer, what is the role of the core material?
A. Increase mechanical strength
B. Decrease magnetic induction
C. Limit saturation
D. Provide overload protection
Answer: C
Explanation: The core material in a protection current transformer is chosen to limit saturation and ensure accurate operation during faults.
What is the primary advantage of using a bushing-type current transformer?
A. Improved accuracy
B. Easy installation
C. Suitable for high-voltage applications
D. Variable transformation ratio
Answer: C
Explanation: Bushing-type current transformers are designed for high-voltage applications, making them suitable for connecting to bushings in electrical equipment.
What is the significance of the burden resistor in the secondary circuit of a current transformer?
A. Increases voltage
B. Decreases voltage
C. Limits current
D. Enhances magnetic induction
Answer: C
Explanation: The burden resistor limits the current flowing through the secondary circuit of a current transformer.
In which scenario would a bar-type current transformer be preferable?
A. Low-voltage circuits
B. Medium-voltage circuits
C. High-voltage circuits
D. Variable frequency circuits
Answer: A
Explanation: Bar-type current transformers are often preferred for accurate current measurement in low-voltage circuits.
What is the primary purpose of a bar-type current transformer in the secondary circuit?
A. Induce voltage
B. Measure current
C. Control frequency
D. Adjust transformation ratio
Answer: B
Explanation: The primary purpose of a bar-type current transformer in the secondary circuit is to measure the current accurately.
What is the function of a current transformer in a protection scheme?
A. Measure voltage
B. Control frequency
C. Provide overcurrent protection
D. Regulate power factor
Answer: C
Explanation: Current transformers play a crucial role in providing overcurrent protection in electrical systems.
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