What is the function of the rotor in an induction motor?
A Induce current
B Rotate with magnetic field
C Supply power
D Generate magnetic field
The rotor in an induction motor rotates as it follows the rotating magnetic field produced by the stator. The induced current in the rotor interacts with the magnetic field, causing the rotor to move and generate mechanical output.
What happens if the load increases in an induction motor?
A Torque decreases
B Speed increases
C Slip increases
D Slip decreases
When the load on an induction motor increases, the rotor slows slightly, which increases slip. This increase in slip allows the motor to produce more torque to meet the additional load.
Which motor type requires an external DC power supply for excitation?
A Synchronous motor
B Stepper motor
C Universal motor
D Induction motor
A synchronous motor requires a DC power supply for its excitation system. This DC power is supplied to the rotor winding, generating the necessary magnetic field for synchronous operation.
What causes rotor currents in an induction motor?
A Through rotor resistance
B External voltage
C Slip rings
D Stator magnetic field
In an induction motor, the stator generates a rotating magnetic field that induces currents in the rotor. These induced currents interact with the magnetic field to produce torque.
What is the key feature of a wound rotor induction motor?
A Squirrel cage rotor
B Permanent magnet
C External resistances
D Slip rings
Wound rotor induction motors have windings on the rotor and use external resistances to control starting torque. These resistances are gradually reduced as the motor reaches its rated speed.
In which type of motor is the rotor always at synchronous speed?
A Synchronous motor
B Universal motor
C Induction motor
D Series motor
In a synchronous motor, the rotor runs at synchronous speed, which is determined by the supply frequency and the number of poles in the motor. This speed remains constant regardless of the load.
What does the slip in an induction motor indicate?
A Difference between rotor and synchronous speed
B Speed of the rotor
C Power consumption
D Current in the rotor
Slip in an induction motor is the difference between the rotor speed and the synchronous speed. It is typically expressed as a percentage of synchronous speed and varies with load.
What does the voltage regulation of a synchronous generator indicate?
A Efficiency of the motor
B Torque capability
C Change in voltage with load
D Stability of frequency
Voltage regulation refers to the change in the output voltage of a synchronous generator as the load varies. A lower voltage regulation indicates better performance in maintaining a constant voltage under varying loads.
What is the primary disadvantage of a single phase induction motor?
A High slip
B Low efficiency
C No starting torque
D High torque
Single phase induction motors do not have inherent starting torque. A phase shifting device, such as a capacitor or auxiliary winding, is required to start the motor by creating a rotating magnetic field.
What type of motor is most commonly used in industrial fans?
A Induction motor
B Universal motor
C Synchronous motor
D Stepper motor
Induction motors are commonly used in industrial fans due to their durability, cost effectiveness, and reliable operation. These motors are ideal for applications requiring moderate to high speeds with constant performance.
What type of rotor is used in most small, low power induction motors?
A Wound rotor
B Slip ring rotor
C Squirrel cage rotor
D Permanent magnet rotor
Squirrel cage rotors are commonly used in small, low power induction motors due to their simplicity, ruggedness, and low maintenance requirements. They are cost effective and efficient for these applications.
What happens in a synchronous motor if excitation is too low?
A Motor operates at higher speed
B Efficiency increases
C Rotor slows down
D Motor loses synchronization
If the excitation in a synchronous motor is too low, the motor will lose synchronization. This causes the rotor to fall out of sync with the rotating magnetic field, and it will not operate correctly.
What is the main advantage of using a three phase system for induction motors?
A Rotor resistance
B Higher efficiency
C Low cost
D Easy maintenance
A three phase system provides a continuous and balanced power supply to induction motors, which improves their efficiency. It also helps in reducing power losses compared to single phase systems.
What is the typical starting method for large induction motors?
A Capacitor starting
B Direct on line starting
C Star delta starting
D Rotor resistance starting
Large induction motors typically use the star delta starting method to reduce the initial current surge. This method connects the windings in a star configuration during startup and switches to delta after the motor reaches a certain speed.
What happens if an induction motor operates at synchronous speed?
A It loses torque production
B It produces maximum torque
C It operates with no slip
D It accelerates further
If an induction motor operates at synchronous speed, there is no relative motion between the rotor and the rotating magnetic field, causing the motor to lose its torque production. Therefore, the motor cannot run at synchronous speed under load.