How Well Do You Know About Electrical Machines? Trivia Quiz

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How Well Do You Know About Electrical Machines? Trivia Quiz - Quiz

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Questions and Answers
  • 1. 

    The basic function of a transformer is to change

    • A.

      The level of the voltage.

    • B.

      The power level.

    • C.

      The power factor.

    • D.

      The frequency.

    Correct Answer
    A. The level of the voltage.
    Explanation
    A transformer is an electrical device that is used to transfer electrical energy between two or more circuits through electromagnetic induction. Its primary function is to change the level of the voltage. This is achieved by utilizing two coils, known as the primary and secondary coils, which are wound around a common core. The primary coil is connected to the input voltage source, while the secondary coil is connected to the load. By varying the number of turns in each coil, the transformer can step up or step down the voltage level, depending on the requirements of the circuit.

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  • 2. 

    Transformer is used

    • A.

      To step up the voltage.

    • B.

      To step down the voltage.

    • C.

      On dc.

    • D.

      To step up or step down the voltage.

    Correct Answer
    D. To step up or step down the voltage.
    Explanation
    A transformer is used to step up or step down the voltage. This is because transformers are designed to transfer electrical energy between two or more circuits through electromagnetic induction. By adjusting the number of windings in the primary and secondary coils, transformers can either increase (step up) or decrease (step down) the voltage level. This allows for efficient transmission of electricity over long distances, as high voltage is more suitable for long-distance transmission while low voltage is safer and more appropriate for domestic use.

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  • 3. 

    An infinite bus-bar has

    • A.

      Constant voltage.

    • B.

      Constant frequency.

    • C.

      Infinite voltage.

    • D.

      Both A and B.

    • E.

      Both B and C.

    Correct Answer
    D. Both A and B.
    Explanation
    An infinite bus-bar refers to a hypothetical power system with an unlimited capacity to supply or absorb power. It is commonly used as a reference point for analyzing power systems. The statement "constant voltage" means that the bus-bar maintains a steady voltage level, regardless of the load or generation. Similarly, "constant frequency" indicates that the bus-bar maintains a consistent frequency of electrical oscillations. Therefore, the correct answer is "both A and B" because an infinite bus-bar has both constant voltage and constant frequency.

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  • 4. 

    Tappings of a transformer are provided

    • A.

      At the phase end of LV side.

    • B.

      At the phase end of HV side.

    • C.

      At the neutral end of HV side.

    • D.

      At the middle of HV side.

    Correct Answer
    D. At the middle of HV side.
    Explanation
    The tappings of a transformer are provided at the middle of HV side. This is because the HV side of the transformer is usually connected to the power grid, which operates at a fixed voltage. However, in some cases, it may be necessary to vary the output voltage of the transformer. By providing tappings at the middle of the HV side, the turns ratio of the transformer can be adjusted, allowing for a variable output voltage. This is particularly useful in situations where the load requirements change or when voltage regulation is necessary.

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  • 5. 

    The auto-transformer is preferably employed in situations where voltage transformation ratio is

    • A.

      Very low.

    • B.

      Near unity.

    • C.

      Very high.

    • D.

      Unity.

    Correct Answer
    B. Near unity.
    Explanation
    An auto-transformer is a type of transformer that has a single winding and is used to step up or step down voltage. It is preferred in situations where the voltage transformation ratio is near unity, meaning that the input and output voltages are very similar. This is because auto-transformers are more efficient and cost-effective compared to regular transformers when the voltage difference is small. Therefore, in scenarios where a small voltage change is required, an auto-transformer is the ideal choice.

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  • 6. 

    An auto-transformer may be used as a/an ___________ transformer.

    • A.

      Power

    • B.

      Distribution

    • C.

      Automatically operated

    • D.

      Voltage regulating

    • E.

      Instrument

    Correct Answer
    D. Voltage regulating
    Explanation
    An auto-transformer is a type of transformer that has a single winding with multiple taps. It can be used as a voltage regulating transformer because it allows for adjusting the output voltage by changing the tap connection. By varying the tap connection, the auto-transformer can step up or step down the voltage, making it useful for regulating voltage levels in electrical systems.

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  • 7. 

    An auto-transformer has

    • A.

      One winding with taps taken out.

    • B.

      Two interlaced windings.

    • C.

      Two windings of same wire.

    • D.

      Two windings of different materials.

    • E.

      One winding without taps.

    Correct Answer
    A. One winding with taps taken out.
    Explanation
    An auto-transformer is a type of transformer that has a single winding with taps taken out. These taps allow for different voltages to be obtained by connecting the load to different points along the winding. This makes the auto-transformer more versatile and efficient compared to a regular transformer with separate primary and secondary windings. The other options, such as two interlaced windings or two windings of different materials, do not accurately describe the configuration of an auto-transformer.

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  • 8. 

    The principle of operation of a 3-phase induction motor closely resembles to that of a

    • A.

      Two winding transformer with its secondary short-circuited.

    • B.

      Two winding transformer with its secondary open-circuited.

    • C.

      Synchronous motor.

    • D.

      Dc shunt motor.

    Correct Answer
    A. Two winding transformer with its secondary short-circuited.
    Explanation
    The principle of operation of a 3-phase induction motor closely resembles that of a two winding transformer with its secondary short-circuited. This is because in both cases, the primary winding (stator in the case of the motor) creates a magnetic field that induces a current in the secondary winding (rotor in the case of the motor). In a transformer, the secondary winding is open-circuited, while in an induction motor, the rotor winding is short-circuited. This allows the motor to self-start and rotate without the need for external connections.

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  • 9. 

    The relative speed between stator and rotor fluxes is equal to

    • A.

      Synchronous speed, Ns.

    • B.

      Rotor speed, N.

    • C.

      Zero

    • D.

      Ns-N

    Correct Answer
    C. Zero
    Explanation
    The relative speed between stator and rotor fluxes is zero because in a synchronous machine, the stator and rotor fluxes rotate at the same speed. This is because the rotor is designed to rotate at the synchronous speed, which is the speed at which the stator magnetic field rotates. Therefore, there is no relative motion between the stator and rotor fluxes, resulting in a relative speed of zero.

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  • 10. 

    An induction motor works with

    • A.

      DC only.

    • B.

      AC only.

    • C.

      AC and DC both.

    • D.

      None of these.

    Correct Answer
    B. AC only.
    Explanation
    An induction motor works with AC only because it relies on the principle of electromagnetic induction to generate a rotating magnetic field. This rotating magnetic field interacts with the rotor, inducing currents that create a torque and cause the rotor to rotate. DC power does not produce a rotating magnetic field, so it cannot be used to operate an induction motor. Therefore, the correct answer is AC only.

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  • 11. 

    The two important parts of an induction motor are

    • A.

      Stator and rotor.

    • B.

      Slip rings and brushes.

    • C.

      Core and winding.

    • D.

      Shaft and ball bearings.

    Correct Answer
    A. Stator and rotor.
    Explanation
    The stator and rotor are indeed the two important parts of an induction motor. The stator is the stationary part of the motor that contains the windings, while the rotor is the rotating part that is connected to the load. The stator creates a rotating magnetic field, which induces currents in the rotor, causing it to rotate. This interaction between the stator and rotor is what allows the motor to convert electrical energy into mechanical energy and perform its intended function.

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  • 12. 

    When two alternators are operating in parallel, if the power input to one of the alternators is cut-off, the alternator will

    • A.

      Continue to run as a synchronous motor rotating in the same direction.

    • B.

      Continue to run as a synchronous motor rotating in opposite direction.

    • C.

      Stop running.

    • D.

      Get damaged due to burning of stator and rotor windings.

    Correct Answer
    A. Continue to run as a synchronous motor rotating in the same direction.
    Explanation
    When two alternators are operating in parallel, they are synchronized and rotating at the same speed. If the power input to one of the alternators is cut off, it will continue to run as a synchronous motor because the other alternator will supply power to it. The synchronous motor will rotate in the same direction as before because it is still synchronized with the other alternator.

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  • 13. 

    A 3-phase synchronous motor will not start if

    • A.

      Voltage is too low.

    • B.

      One phase is open.

    • C.

      Connections are faulty.

    • D.

      Any of the above.

    Correct Answer
    D. Any of the above.
    Explanation
    The correct answer is "any of the above" because all three conditions mentioned (voltage is too low, one phase is open, connections are faulty) can prevent a 3-phase synchronous motor from starting. If the voltage is too low, the motor may not have enough power to start. If one phase is open, there will be an imbalance in the motor's operation, preventing it from starting. Similarly, if the connections are faulty, it can disrupt the motor's functioning and prevent it from starting. Therefore, any of these conditions can hinder the motor's starting.

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  • 14. 

    Synchronous motors are inherently not self-starting motors as

    • A.

      The direction of instantaneous torque on the rotor reverses after each half cycle.

    • B.

      There is no slip.

    • C.

      The stator does not produce revolving magnetic field.

    • D.

      It has no starting winding.

    Correct Answer
    A. The direction of instantaneous torque on the rotor reverses after each half cycle.
    Explanation
    Synchronous motors are not self-starting because the direction of instantaneous torque on the rotor reverses after each half cycle. This means that the rotor cannot continuously rotate in one direction to start the motor on its own. It requires an external force or mechanism to initially rotate the rotor and synchronize it with the rotating magnetic field produced by the stator. Once the motor is synchronized, it can maintain its speed and operation due to the constant reversal of torque during each half cycle.

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  • 15. 

    Which of the following electric motors is not inherently self starting motor?

    • A.

      Synchronous motor.

    • B.

      3-phase induction motor.

    • C.

      Reluctance motor.

    • D.

      DC series motor.

    Correct Answer
    A. Synchronous motor.
    Explanation
    A synchronous motor is not inherently self-starting because it requires an external power source to initially rotate the rotor at synchronous speed before it can start operating on its own. In contrast, the other three motors mentioned in the options (3-phase induction motor, reluctance motor, and DC series motor) are inherently self-starting, meaning they can start and operate without the need for any external assistance.

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  • 16. 

    In a synchronous motor, squirrel cage winding is provided for making motor

    • A.

      Noise free.

    • B.

      Self starting.

    • C.

      Cheap.

    • D.

      Quick start.

    Correct Answer
    B. Self starting.
    Explanation
    The squirrel cage winding in a synchronous motor allows it to be self-starting. This means that the motor can start running on its own without the need for any external assistance or additional devices. The squirrel cage winding provides the necessary torque to initiate the rotation of the motor, allowing it to start and operate smoothly. This feature is advantageous as it eliminates the need for manual intervention or additional starting mechanisms, making the motor more convenient and efficient to use.

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  • 17. 

    The method that can be used conveniently for speed control of a squirrel cage induction motor is

    • A.

      Pole changing control.

    • B.

      Rotor resistance control.

    • C.

      Cascade operation.

    • D.

      Secondary foreign voltage control.

    Correct Answer
    A. Pole changing control.
    Explanation
    Pole changing control is a method that allows for convenient speed control of a squirrel cage induction motor. This technique involves altering the number of poles in the motor by changing the connections of the stator winding. By changing the number of poles, the motor's speed can be adjusted to meet the desired requirements. This method is commonly used in applications where variable speed control is necessary, such as in industrial processes or electric vehicles. Rotor resistance control, cascade operation, and secondary foreign voltage control are not as commonly used or as convenient for speed control in squirrel cage induction motors.

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  • 18. 

    If the prime-mover of an alternator supplying load to an infinite bus is suddenly shut down, then it will

    • A.

      Stop.

    • B.

      Continue to run as an alternator.

    • C.

      Continue to run as a synchronous motor in the reverse direction.

    • D.

      Continue to run as a synchronous motor in the same direction.

    Correct Answer
    D. Continue to run as a synchronous motor in the same direction.
    Explanation
    When the prime-mover of an alternator supplying load to an infinite bus is suddenly shut down, the alternator will continue to run as a synchronous motor in the same direction. This is because the alternator is connected to an infinite bus, which provides a constant voltage and frequency. The alternator will act as a synchronous motor, converting electrical energy into mechanical energy to keep rotating in the same direction. It will continue to provide power to the infinite bus and maintain system stability.

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  • 19. 

    While starting a synchronous motor its field winding should be

    • A.

      Kept open.

    • B.

      Short-circuited.

    • C.

      Connected to a DC source.

    • D.

      None of the above.

    Correct Answer
    B. Short-circuited.
    Explanation
    When starting a synchronous motor, its field winding should be short-circuited. This is because a synchronous motor relies on the interaction between the stator's magnetic field and the rotor's magnetic field to operate. By short-circuiting the field winding, the motor can generate its own magnetic field without the need for an external DC source. This allows the motor to start and synchronize with the power supply, ensuring efficient operation.

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  • 20. 

    Synchronous capacitor is

    • A.

      An ordinary static capacitor bank.

    • B.

      An over-excited synchronous motor driving mechanical load.

    • C.

      An over-excited synchronous motor without mechanical load.

    • D.

      None of the above.

    Correct Answer
    C. An over-excited synchronous motor without mechanical load.
    Explanation
    A synchronous capacitor is an over-excited synchronous motor without mechanical load. This means that it operates as a capacitor bank, providing reactive power support to the electrical system. It does not have a mechanical load to drive, so its sole purpose is to correct the power factor and improve the efficiency of the system. It is different from an ordinary static capacitor bank because it is a motor that generates its own magnetic field and requires an excitation source.

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  • 21. 

    When the induction motor is in standstill, the slip is

    • A.

      Zero.

    • B.

      1.

    • C.

      Infinity.

    • D.

      None of the above.

    Correct Answer
    B. 1.
    Explanation
    When the induction motor is in standstill, the slip is zero. Slip is defined as the difference between the synchronous speed of the motor and the actual speed of the rotor. In standstill, the rotor is not moving, so there is no difference in speed. Therefore, the slip is zero.

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  • 22. 

    An electric motor gets over-heated. This may be due to

    • A.

      Over-loading.

    • B.

      Shorted stator winding.

    • C.

      Worn-out or dry bearings.

    • D.

      Low or high voltage.

    • E.

      Any of the above.

    Correct Answer
    E. Any of the above.
    Explanation
    The correct answer is "any of the above" because all of the mentioned factors can lead to the overheating of an electric motor. Over-loading can cause excessive current flow and heat generation, shorted stator winding can result in increased resistance and heat buildup, worn-out or dry bearings can cause friction and heat, and low or high voltage can affect the motor's efficiency and heat dissipation. Therefore, any of these factors can contribute to the motor getting over-heated.

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  • 23. 

    A squirrel cage induction motor is not favoured when _______________ is the main consideration.

    • A.

      Initial cost.

    • B.

      Maintenance cost.

    • C.

      High starting torque.

    • D.

      Higher efficiency and higher power factor.

    Correct Answer
    C. High starting torque.
    Explanation
    A squirrel cage induction motor is not favored when high starting torque is the main consideration. This is because squirrel cage induction motors typically have lower starting torque compared to other types of motors, such as wound rotor motors. In applications where high starting torque is required, such as in heavy machinery or equipment that needs to overcome initial resistance, other motor types may be more suitable.

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  • 24. 

    Which of the following ac motor is widely used?

    • A.

      Squirrel cage induction motor.

    • B.

      Slip-ring induction motor.

    • C.

      Double cage induction motor.

    • D.

      Synchronous motor.

    Correct Answer
    A. Squirrel cage induction motor.
    Explanation
    The squirrel cage induction motor is widely used in various applications due to its simplicity, reliability, and cost-effectiveness. It consists of a rotor with conductive bars resembling a squirrel cage, which allows for efficient power transmission and smooth operation. Unlike the slip-ring induction motor, it does not require external resistance or maintenance of the slip rings and brushes. The double cage induction motor is less common and used for specific high-torque applications. The synchronous motor is not an AC motor but operates at a constant speed and is typically used in applications requiring precise control of speed and power factor.

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  • 25. 

    A slip-ring induction motor is recommended for applications requiring

    • A.

      High starting torque.

    • B.

      Variable speed operation.

    • C.

      Frequent starting, stopping and reversing operations.

    • D.

      All of the above features.

    Correct Answer
    D. All of the above features.
    Explanation
    A slip-ring induction motor is recommended for applications requiring high starting torque because it has the ability to provide a high level of torque during startup. It is also suitable for variable speed operation as it can be controlled by adjusting the resistance in the rotor circuit. Additionally, slip-ring induction motors are ideal for frequent starting, stopping, and reversing operations due to their robust construction and ability to handle high levels of mechanical stress. Therefore, it can be concluded that a slip-ring induction motor is recommended for applications requiring all of the above features.

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  • 26. 

    In a 3-phase induction motor, iron loss mainly occurs in

    • A.

      Stator and rotor.

    • B.

      Rotor core and rotor teeth.

    • C.

      Stator core and stator teeth.

    • D.

      Stator winding.

    Correct Answer
    C. Stator core and stator teeth.
    Explanation
    In a 3-phase induction motor, iron loss mainly occurs in the stator core and stator teeth. Iron loss refers to the energy dissipated in the form of heat due to the magnetic properties of the iron core and teeth. The stator core and teeth experience flux variations, resulting in hysteresis and eddy current losses. These losses are minimized by using high-quality laminated iron cores and optimizing the design of the stator teeth. Therefore, the stator core and stator teeth are the primary locations where iron loss occurs in a 3-phase induction motor.

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  • 27. 

    The operation of an induction motor is based on

    • A.

      Lenz's law.

    • B.

      Ampere's law.

    • C.

      Principle of mutual induction.

    • D.

      Principle of self induction.

    Correct Answer
    C. Principle of mutual induction.
    Explanation
    The operation of an induction motor is based on the principle of mutual induction. Mutual induction occurs when a changing current in one coil induces a voltage in a nearby coil. In an induction motor, the primary coil (stator) creates a rotating magnetic field, which then induces a current in the secondary coil (rotor). This induced current in the rotor creates a magnetic field that interacts with the stator's field, causing the rotor to rotate. This principle of mutual induction allows for the conversion of electrical energy into mechanical energy in an induction motor.

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  • 28. 

    A dc motor can be easily identified by

    • A.

      Yoke

    • B.

      Size of conductor

    • C.

      Commutator

    • D.

      Winding

    Correct Answer
    C. Commutator
    Explanation
    A DC motor can be easily identified by the presence of a commutator. The commutator is a device that helps to switch the direction of the current flowing through the motor's coils, thereby allowing it to rotate continuously in one direction. This distinguishes a DC motor from other types of motors, such as AC motors, which do not have a commutator. The yoke, size of conductor, and winding are important components of a DC motor, but they are not exclusive to DC motors and can also be found in other types of motors.

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  • 29. 

    The function of the starter for a dc motor is

    • A.

      To limit the starting current.

    • B.

      To limit the starting voltage.

    • C.

      To increase field resistance.

    • D.

      To reduce armature resistance.

    Correct Answer
    A. To limit the starting current.
    Explanation
    The function of the starter for a DC motor is to limit the starting current. This is important because when a DC motor starts, it experiences a surge of current which can be very high and potentially damaging. The starter helps to control this current surge and prevent any harm to the motor or the electrical system. By limiting the starting current, the starter ensures a smooth and controlled start for the motor, allowing it to operate safely and efficiently.

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  • 30. 

    In a transformer, electrical power is transferred from one circuit to another without change in

    • A.

      Voltage.

    • B.

      Current.

    • C.

      Frequency.

    • D.

      Turns.

    Correct Answer
    C. Frequency.
    Explanation
    In a transformer, electrical power is transferred from one circuit to another without a change in frequency. This is because transformers work based on the principle of electromagnetic induction, which involves the transfer of energy through a varying magnetic field. The primary and secondary windings of a transformer are designed to have a specific number of turns, which allows for the desired voltage transformation. However, the frequency of the alternating current remains constant throughout the process, ensuring efficient power transfer.

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  • 31. 

    The efficiency of a power transformer is around

    • A.

      50%

    • B.

      60%

    • C.

      80%

    • D.

      95%

    Correct Answer
    D. 95%
    Explanation
    The efficiency of a power transformer refers to the ratio of output power to input power, expressed as a percentage. A higher efficiency percentage indicates that the transformer is able to convert a larger proportion of the input power into useful output power, while minimizing losses. In this case, the correct answer of 95% suggests that the power transformer is highly efficient, with only a small amount of power being lost during the transformation process.

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  • 32. 

    Transformer action requires a

    • A.

      Constant magnetic flux.

    • B.

      Incrasing magnetic flux.

    • C.

      Alternating magnetic flux.

    • D.

      Alternating electric flux.

    Correct Answer
    C. Alternating magnetic flux.
    Explanation
    Transformer action requires an alternating magnetic flux. This is because a transformer operates on the principle of electromagnetic induction, where a changing magnetic field induces a voltage in a nearby coil. In a transformer, an alternating current flowing through the primary coil creates an alternating magnetic field, which then induces a voltage in the secondary coil. This alternating magnetic flux is essential for the transfer of energy between the primary and secondary coils in a transformer.

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  • 33. 

    In a transformer operating at constant voltage, if the input frequency increases, the core loss

    • A.

      Increases.

    • B.

      Decreases.

    • C.

      Remains constant.

    • D.

      Increases as square of the frequency.

    Correct Answer
    B. Decreases.
    Explanation
    When a transformer operates at a constant voltage, an increase in input frequency leads to a decrease in core loss. This is because core loss is primarily caused by hysteresis and eddy current losses, which are directly proportional to the frequency. Therefore, as the frequency increases, the core loss decreases.

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  • 34. 

    The inductive reactance of a transformer depends on

    • A.

      Electromotive force.

    • B.

      Magnetomotive force.

    • C.

      Magnetic flux.

    • D.

      Leakage flux.

    Correct Answer
    D. Leakage flux.
    Explanation
    The inductive reactance of a transformer depends on the leakage flux. Leakage flux refers to the magnetic flux that does not link both the primary and secondary windings of a transformer. This flux is caused by the imperfect coupling between the windings and is responsible for energy losses in the transformer. The inductive reactance is a measure of the opposition to the flow of alternating current due to the presence of inductance. In a transformer, the presence of leakage flux increases the inductance, which in turn increases the inductive reactance. Therefore, the correct answer is leakage flux.

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  • 35. 

    The speed of single phase induction motors can be controlled by

    • A.

      Varying the applied voltage to the stator winding.

    • B.

      Varying the number of poles on the stator.

    • C.

      Either A or B.

    • D.

      None of these.

    Correct Answer
    C. Either A or B.
    Explanation
    The speed of single phase induction motors can be controlled by either varying the applied voltage to the stator winding or varying the number of poles on the stator. By adjusting the voltage applied to the stator winding, the speed of the motor can be increased or decreased. Similarly, by changing the number of poles on the stator, the speed of the motor can also be controlled. Therefore, either option A or B can be used to control the speed of single phase induction motors.

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  • 36. 

    The wattage rating for a ceiling motor will be in the range

    • A.

      50 to 250W.

    • B.

      250 to 500W.

    • C.

      50 to 150W.

    • D.

      10 to 20W.

    Correct Answer
    C. 50 to 150W.
    Explanation
    The wattage rating for a ceiling motor is typically in the range of 50 to 150W. This range is suitable for most ceiling fans, as they require a moderate amount of power to operate efficiently. A wattage rating below 50W may indicate a motor that is not powerful enough to effectively circulate air, while a rating above 150W may suggest a motor that is too powerful and consumes excessive energy. Therefore, the range of 50 to 150W is the most appropriate and common wattage rating for a ceiling motor.

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  • 37. 

    If a dc series motor is operated on ac supply, it

    • A.

      Will not start at all.

    • B.

      Will start and run but will have poor performance such as excessive sparking, poor efficiency and poor power factor.

    • C.

      Will get damaged due to burning of its windings.

    • D.

      Will run at excessively high speed.

    Correct Answer
    B. Will start and run but will have poor performance such as excessive sparking, poor efficiency and poor power factor.
    Explanation
    When a DC series motor is operated on an AC supply, it will start and run, but it will have poor performance. This is because the AC supply causes the motor to experience excessive sparking, resulting in reduced efficiency and a poor power factor. The motor may also struggle to maintain a steady speed and may exhibit fluctuations in its performance. However, it will not be completely damaged or run at excessively high speeds.

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  • 38. 

    A universal motor is one which has

    • A.

      Constant speed.

    • B.

      Constant output.

    • C.

      Capability of operating both on ac and dc with comparable performance.

    • D.

      Maximum efficiency

    Correct Answer
    C. Capability of operating both on ac and dc with comparable performance.
    Explanation
    A universal motor is designed to operate on both AC (alternating current) and DC (direct current) power sources with comparable performance. This means that the motor can function efficiently and effectively regardless of whether it is connected to an AC or DC power supply. This versatility makes universal motors suitable for a wide range of applications where the power source may vary, such as in household appliances, power tools, and electric vehicles.

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  • 39. 

    Phase advancers are employed with large induction motors to

    • A.

      Regulate their speeds.

    • B.

      Reduce copper losses.

    • C.

      Improve power factor.

    • D.

      Reduce noise and vibrations.

    Correct Answer
    C. Improve power factor.
    Explanation
    Phase advancers are devices used with large induction motors to improve their power factor. Power factor is a measure of how effectively electrical power is being used, and a low power factor can result in increased energy consumption and higher electricity bills. By improving the power factor, phase advancers help to optimize the efficiency of the motor and reduce the amount of reactive power required, leading to energy savings and improved overall performance.

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  • 40. 

    Which motor can conveniently operate at lagging as well as leading power factor?

    • A.

      Squirrel-cage induction motor.

    • B.

      Wound rotor induction motor.

    • C.

      Synchronous motor.

    • D.

      DC shunt motor.

    Correct Answer
    C. Synchronous motor.
    Explanation
    A synchronous motor can conveniently operate at both lagging and leading power factor because it has the ability to adjust its field excitation to match the load requirements. By controlling the excitation, the motor can either provide reactive power to the system (leading power factor) or absorb reactive power from the system (lagging power factor). This flexibility makes the synchronous motor suitable for applications where power factor correction is required or where the motor needs to operate at different power factors depending on the load conditions.

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  • 41. 

    The speed of a synchronous motor

    • A.

      Remains constant from no load to full load.

    • B.

      Varies with the variation in load.

    • C.

      Decreases with the increase in load.

    • D.

      Increases with the increase in load.

    Correct Answer
    A. Remains constant from no load to full load.
    Explanation
    The speed of a synchronous motor remains constant from no load to full load. This is because a synchronous motor operates at synchronous speed, which is determined by the frequency of the power supply and the number of poles in the motor. Regardless of the load, the synchronous motor will maintain its synchronous speed, making it ideal for applications that require a constant speed, such as in power plants or in synchronous clocks.

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  • 42. 

    In parallel operation, load sharing by transformers is according to

    • A.

      Per unit impedance.

    • B.

      KVA rating.

    • C.

      KW rating.

    • D.

      Efficiency.

    Correct Answer
    A. Per unit impedance.
    Explanation
    In parallel operation, load sharing by transformers is according to per unit impedance. This means that the transformers share the load based on their respective per unit impedance values. Transformers with lower impedance will take on a larger portion of the load, while transformers with higher impedance will take on a smaller portion. This ensures that the load is distributed evenly among the transformers, preventing overloading of any single transformer. The per unit impedance is a measure of the transformer's ability to handle the load, so it is used as a basis for load sharing in parallel operation.

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  • 43. 

    A distribution transformer is selected on the basis of

    • A.

      Voltage regulation.

    • B.

      Efficiency.

    • C.

      All day efficiency.

    • D.

      None of these.

    Correct Answer
    C. All day efficiency.
    Explanation
    A distribution transformer is selected on the basis of all day efficiency, as it is important to consider how efficiently the transformer can convert electrical energy from the primary side to the secondary side over a 24-hour period. All day efficiency takes into account the transformer's performance under varying load conditions throughout the day, ensuring that it operates efficiently and minimizes energy losses. Voltage regulation and efficiency are also important factors, but all day efficiency provides a more comprehensive evaluation of the transformer's overall performance.

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  • 44. 

    The function of oil in a transformer is

    • A.

      To provide insulation and cooling.

    • B.

      To provide protection against lightning.

    • C.

      To provide protection against short-circuit.

    • D.

      To provide lubrication.

    Correct Answer
    A. To provide insulation and cooling.
    Explanation
    The function of oil in a transformer is to provide insulation and cooling. Oil acts as an insulating medium between the transformer windings, preventing electrical breakdown and ensuring the safe transfer of electrical energy. Additionally, oil also helps in dissipating heat generated during operation, thus keeping the transformer cool and preventing overheating.

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Quiz Review Timeline +

Our quizzes are rigorously reviewed, monitored and continuously updated by our expert board to maintain accuracy, relevance, and timeliness.

  • Current Version
  • Mar 22, 2022
    Quiz Edited by
    ProProfs Editorial Team
  • Jul 26, 2007
    Quiz Created by
    Eeecusat
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