What is the primary function of the stator in an induction motor?
A Supply current
B Generate torque
C Create magnetic field
D Regulate speed
Mechanical engineering focuses on the design, analysis, and manufacturing of mechanical systems. It involves studying forces, materials, and energy to create machines, tools, and mechanical structures. This field applies engineering principles to develop functional and efficient products across industries like automotive, aerospace, and energy.
What is the rotor type commonly used in most induction motors?
A Squirrel-cage rotor
B Slip ring rotor
C Wound rotor
D Permanent magnet rotor
Squirrel-cage rotors are commonly used in most induction motors because they are simple, robust, and require minimal maintenance. They consist of conductive bars shorted at both ends, forming a closed loop.
What does the term ‘synchronous speed’ refer to?
A Speed of rotor rotation
B Speed at which the magnetic field rotates
C Speed at maximum torque
D Speed of induced current
Synchronous speed refers to the speed at which the magnetic field created by the stator rotates. This is determined by the supply frequency and the number of poles in the motor.
What is ‘slip’ in an induction motor?
A Difference in voltages
B Rotor resistance
C Difference between synchronous and rotor speed
D Power loss
Slip in an induction motor is the difference between the synchronous speed and the actual rotor speed. It is usually expressed as a percentage of the synchronous speed and indicates how much slower the rotor moves compared to the magnetic field.
Which component is used for starting an induction motor?
A Capacitor
B Stator windings
C Slip rings
D Rotor
A capacitor is used in some types of induction motors (such as capacitor start motors) to create a phase shift for the starting torque. It helps in overcoming the initial resistance and enables smooth starting.
What causes core losses in an induction motor?
A Windage losses
B Friction
C Eddy currents and hysteresis
D Slip rings
Core losses in an induction motor are primarily due to eddy currents and hysteresis in the core material. These losses are a result of the changing magnetic field in the stator core, which leads to the generation of heat.
Which method is commonly used to brake an induction motor?
A Regenerative braking
B Plugging
C Dynamic braking
D All of the above
Induction motors can be braked by various methods, including regenerative braking (reversing the motor’s direction to generate power), plugging (reversing the current), and dynamic braking (using resistors to dissipate energy).
What is the function of the rotor windings in a wound rotor induction motor?
A Create a cooling effect
B Induce a rotating magnetic field
C Supply electrical power
D Provide starting torque
The rotor windings in a wound rotor induction motor are connected to external resistances during startup to provide high starting torque. These resistances are gradually reduced once the motor reaches running speed.
In which type of motor is synchronous speed achieved?
A Universal motor
B Induction motor
C Synchronous motor
D Slip ring motor
A synchronous motor operates at synchronous speed, meaning the rotor speed matches the magnetic field’s speed. This is different from an induction motor, where the rotor speed is always slightly less than the synchronous speed.
What is the role of the excitation system in a synchronous motor?
A Maintain constant flux
B Control rotor speed
C Increase voltage
D Provide mechanical power
The excitation system in a synchronous motor provides the necessary DC supply to the rotor winding to generate the magnetic field needed for synchronous operation. It ensures that the flux remains constant and the motor runs at synchronous speed.
What is the impact of an increase in the load on an induction motor?
A Decreases torque
B Increases slip
C Decreases efficiency
D Increases power factor
As the load on an induction motor increases, the rotor speed decreases slightly, causing an increase in slip. The slip increases to provide more torque to handle the added load.
What does the term ‘voltage regulation’ mean in a synchronous machine?
A Control of excitation
B Control of rotor speed
C Change in output voltage with load
D Control of stator resistance
Voltage regulation refers to the change in the output voltage of a synchronous machine as the load varies. Good voltage regulation indicates that the machine can maintain a nearly constant voltage even when the load changes.
Which of the following is a key feature of squirrel-cage rotors in induction motors?
A Simple and rugged design
B Provide adjustable speed
C Use external resistors
D Require slip rings
Squirrel-cage rotors are known for their simplicity and rugged design, as they do not require slip rings or brushes. Their robust construction makes them highly reliable and low maintenance.
What type of electrical system is commonly used to operate synchronous motors?
A DC system
B Dual phase system
C Single phase system
D Three phase system
Synchronous motors are most commonly operated in three phase systems. This type of system provides the balanced voltage necessary for synchronous operation, ensuring stable performance of the motor.
How does the torque speed characteristic of an induction motor look?
A Parabolic
B S shaped
C Asymptotic
D Linear
The torque speed characteristic of an induction motor typically follows an S shape. At low speeds, the torque increases rapidly, then decreases as the motor approaches synchronous speed. At full speed, the torque is minimal.