Test: Single-Phase Induction Motors - 1 - Electrical Engineering (EE) MCQ

• Split-phase motor: A split-phase motor is a type of single-phase induction motor that has two windings known as the main winding and the auxiliary winding.


• Starting winding: The starting winding is used to provide the initial torque necessary to start the motor.


• Centrifugal switch: In a split-phase motor, the starting winding is connected through a centrifugal switch. The centrifugal switch is a device that is activated by the motor's rotation speed. When the motor reaches a certain speed, the centrifugal switch disconnects the starting winding from the circuit to prevent overheating and damage to the motor.


• Function of centrifugal switch: The centrifugal switch ensures that the starting winding is only active during the startup phase of the motor and is disconnected once the motor reaches its operating speed.


• Running winding: The running winding is the winding responsible for providing the continuous torque needed to keep the motor running once it has started.


• Conclusion: In a split-phase motor, the starting winding is connected through a centrifugal switch to control its operation and prevent overheating, making option A the correct answer.

• Ceiling Fan Motor: A ceiling fan motor typically employs a capacitor run motor for efficient operation.


• Primary and Secondary Windings: In a capacitor run motor, the secondary winding surrounds the primary winding.


• Function: The primary winding is responsible for creating a magnetic field when an alternating current passes through it. The secondary winding then interacts with this magnetic field to generate the torque required to drive the fan blades.


• Efficiency: This arrangement of windings ensures efficient operation of the ceiling fan motor, providing the necessary power to circulate air effectively.


• Common Arrangement: The primary winding being surrounded by the secondary winding is a usual arrangement in capacitor run motors used in ceiling fans.

• Gradually varying load: Cranes and hoists often deal with loads that gradually increase or decrease in weight over time. This type of load requires careful control and precision in lifting and moving.


• Non-reversing, no-load start: Some cranes and hoists may encounter situations where they need to start moving a load without any reversing motion and without any initial load. This type of start requires a different set of controls and mechanisms.


• Reversing, light start: In some cases, cranes and hoists may need to lift a light load that requires reversing motion at the start. This type of load also requires precise control to ensure the safety of the operation.


• Reversing, heavy start: Cranes and hoists may also encounter situations where they need to lift a heavy load with reversing motion at the start. This type of load is challenging and requires strong and reliable equipment to handle the weight.

In conclusion, cranes and hoists offer a variety of loads, each requiring specific control and handling techniques to ensure safe and efficient operation.

• Low Noise: Hysteresis motors are known for their quiet operation, making them ideal for tape recorders where noise can affect the recording quality.



• Smooth Operation: Hysteresis motors provide smooth and consistent rotation, which is crucial for maintaining a steady tape speed in tape recorders.



• Low Maintenance: These motors have a simple design with few moving parts, resulting in low maintenance requirements, which is beneficial for long-term use in tape recorders.



• High Torque: Hysteresis motors offer high starting torque, allowing them to quickly reach the desired rotational speed for tape recorder applications.



• Stable Speed: These motors have excellent speed stability, ensuring accurate recording and playback speeds in tape recorders.

• Universal motor: Mixies typically use universal motors due to their high speed and ability to generate high torque at low speeds, making them ideal for blending and grinding tasks.


• Characteristics of universal motors:
  
  
  
  • Can operate on both AC and DC power sources.
  
  
  • High speed and high torque capabilities.
  
  
  • Compact and lightweight design.
  
  
  • Cost-effective compared to other motor types.
  
  
  
  


• Working principle:
  
  
  
  • Universal motors operate on the principle of electromagnetism, where an electric current passing through a coil in a magnetic field generates rotational motion.
  
  
  • They have a commutator and brushes to ensure the continuous flow of current, allowing them to run efficiently at varying speeds.
  
  
  
  


• Applications:
  
  
  
  • Aside from mixies, universal motors are used in power tools, vacuum cleaners, and kitchen appliances due to their versatility and performance capabilities.
  
  
  
  

• Hysteresis Loss: A hysteresis motor operates based on hysteresis loss, which is the energy lost when a magnetic material is magnetized in one direction and then demagnetized.


• Rotating Magnetic Field: The stator of the motor generates a rotating magnetic field, which induces eddy currents in the rotor.


• Permanent Magnet Rotor: The rotor of a hysteresis motor is made of a material with high hysteresis loss characteristics, such as a permanent magnet material.


• Delayed Alignment: The hysteresis loss in the rotor material causes a delay in alignment with the rotating magnetic field, resulting in the rotor rotating in the same direction as the magnetic field.


• Low Slip: Hysteresis motors have low slip, meaning the rotor speed closely follows the speed of the rotating magnetic field.

• Step 1: Determine the horsepower (HP) rating of the motor.


• Step 2: Calculate the power factor of the motor.


• Step 3: Use the formula: Starting Capacitor (in uF) = 1350 x HP / (Voltage x Power Factor)

• Horsepower (HP) Rating: Fractional horsepower motors typically have a rating of less than 1 HP.


• Power Factor: The power factor of a motor is typically between 0.8 and 0.9.


• Formula: The formula for calculating the starting capacitor value takes into account the horsepower, voltage, and power factor of the motor.


• Value: For a fractional horsepower motor, the starting capacitor value is typically around 300 uF.

• Two value capacitor motor: In a two value capacitor motor, two capacitors are used - one for starting purposes and the other for running purposes.


• Capacitor for running purposes: The capacitor used for running purposes in a two value capacitor motor is typically a paper spaced oil filled type capacitor.


• Paper spaced oil filled type capacitor: This type of capacitor is designed to handle the continuous operation and voltage requirements of the motor during its running cycle.


• Advantages of paper spaced oil filled type capacitor:
  
  
  
  • High reliability and durability
  
  
  • Good performance in continuous running conditions
  
  
  • Ability to handle the heat generated during motor operation
  
  
  
  

• Current in the starting winding leads the voltage: In capacitor start single-phase motors, the starting winding is connected in series with a capacitor. This creates a phase shift between the current and voltage in the starting winding. The current in the starting winding leads the voltage, creating a rotating magnetic field that helps in starting the motor.

• Role of the Rotor: The rotor in a hysteresis motor plays a crucial role in the operation of the motor.


• Requirement of Retentivity: The rotor must have retentivity, which is the ability to retain magnetization even after the magnetizing force is removed.


• Importance of Retentivity: Retentivity in the rotor ensures that the motor maintains a constant magnetic field, which is essential for its operation.


• Effect on Motor Performance: Without retentivity in the rotor, the motor would not be able to generate the necessary torque to function effectively.


• Conclusion: Therefore, it is essential for the rotor in a hysteresis motor to have retentivity to ensure smooth and efficient operation of the motor.