What is the function of slip rings in an induction motor?
A Maintain rotor speed
B Supply power
C Connect rotor windings
D Control torque
Slip rings are used to provide a continuous connection to the rotor windings in certain types of induction motors, such as wound rotor motors. This allows for the external resistance to be connected for starting torque.
Which type of rotor is used in wound rotor induction motors?
A Wound rotor
B Slip ring rotor
C Squirrel cage rotor
D Permanent magnet rotor
Wound rotors are used in some induction motors to offer external resistance during startup. This provides high starting torque and smooth acceleration. They are typically connected via slip rings.
In a synchronous motor, what is the relationship between rotor speed and magnetic field?
A Slightly slower
B Faster
C Unrelated
D Same
In a synchronous motor, the rotor speed must match the speed of the magnetic field created by the stator. This means the rotor rotates at synchronous speed, which is determined by the supply frequency.
Which motor is commonly used in applications requiring constant speed?
A Universal motor
B Induction motor
C Synchronous motor
D Series motor
A synchronous motor operates at constant speed, regardless of load, since its rotor speed matches the magnetic field speed. This makes it ideal for applications needing precise speed control.
What is a key characteristic of a squirrel cage rotor?
A Requires slip rings
B Robust and maintenance free
C External resistors
D High starting torque
Squirrel cage rotors are simple and rugged, offering low maintenance. They do not require external resistors or slip rings, which makes them a popular choice for general purpose induction motors.
What does the term ‘synchronous speed’ depend on in a synchronous motor?
A Frequency and poles
B Core material
C Load applied
D Rotor resistance
The synchronous speed of a motor depends on the supply frequency and the number of poles in the stator winding. It is calculated by the formula Ns = (120f)/P, where f is frequency and P is the number of poles.
What type of motor is most commonly used in home appliances?
A Universal motor
B Synchronous motor
C Induction motor
D Stepper motor
Induction motors are widely used in home appliances due to their simplicity, cost effectiveness, and reliability. They operate on AC power and require minimal maintenance.
What is the purpose of using a capacitor in a single phase induction motor?
A Reduce slip
B Create phase shift
C Improve efficiency
D Increase speed
In a single phase induction motor, a capacitor is used to create a phase shift between the stator windings, which helps in generating a rotating magnetic field necessary for starting and running the motor.
What is the primary cause of losses in the rotor of an induction motor?
A Slip rings
B Magnetic interference
C Eddy currents
D Stator losses
Eddy currents are induced in the rotor due to the changing magnetic field from the stator, which causes energy losses. These losses generate heat and reduce the efficiency of the motor.
How does an induction motor produce torque?
A Through a moving magnetic field
B By mechanical means
C Using capacitors
D By external power supply
In an induction motor, torque is produced due to the interaction between the rotating magnetic field generated by the stator and the current induced in the rotor. This causes the rotor to turn and produce mechanical torque.
In a synchronous motor, what happens if the excitation is lost?
A The motor operates at lower torque
B The motor runs at high speed
C The motor speeds up
D The motor stops synchronizing
If excitation is lost in a synchronous motor, the rotor will no longer be magnetized, causing the motor to lose synchronization. It will no longer run at synchronous speed and may stop.
What is the impact of increasing load on an induction motor’s slip?
A Causes the motor to stop
B Increases slip
C No effect on slip
D Decreases slip
As the load on an induction motor increases, the rotor speed decreases slightly, leading to an increase in slip. This allows the motor to generate more torque to handle the additional load.
Which type of motor is ideal for applications requiring precise speed control and constant speed?
A Universal motor
B Shaded pole motor
C Synchronous motor
D Induction motor
Synchronous motors are ideal for applications requiring precise and constant speed control because they run at synchronous speed, which does not change with varying loads.
What is the effect of core losses in an induction motor?
A Improve torque
B Have no effect
C Increase efficiency
D Reduce efficiency
Core losses, which include eddy current and hysteresis losses, generate heat in the motor’s core and reduce efficiency. These losses occur due to the alternating magnetic field in the stator.
Which of the following factors determines the power factor of an induction motor?
A Load and excitation
B Rotor speed
C Load current
D Stator resistance
The power factor of an induction motor is determined by the load applied and the motor’s excitation. The load affects the motor’s current draw and the phase difference between voltage and current, which influences the power factor.