Induction and Synchronous Machines MCQs (Part-14)

What is the primary function of the stator winding in a synchronous motor?

A To supply current to the rotor
B To create the rotating magnetic field
C To provide mechanical power
D To regulate the motor’s speed

How does increasing the slip in an induction motor affect the torque?

A Torque increases
B Torque decreases
C Torque remains constant
D Torque becomes unstable

What is the main effect of harmonic currents in induction motors?

A They increase motor efficiency
B They cause overheating and reduce efficiency
C They reduce the motor’s power factor
D They stabilize the motor’s speed

Which of the following is a common starting method for large induction motors?

A Direct-on-line (DOL) starting
B Star-delta starting
C Capacitor start
D Both A and B

What happens when the slip of an induction motor is zero?

A The motor reaches maximum torque
B The rotor speed matches the synchronous speed
C The motor runs without producing power
D The rotor current becomes zero

What is the primary reason for using squirrel-cage rotors in induction motors?

A To improve the motor’s speed control
B To reduce maintenance costs
C To increase starting torque
D To improve the power factor

What happens when the excitation of a synchronous motor is increased?

A The motor’s speed increases
B The power factor becomes leading
C The power factor becomes lagging
D The motor’s efficiency decreases

How does increasing the slip in an induction motor affect the motor’s efficiency?

A The motor becomes more efficient
B The motor becomes less efficient
C The motor’s efficiency remains constant
D The motor becomes more powerful

What is the primary role of the stator winding in an induction motor?

A To create the magnetic field that induces current in the rotor
B To provide mechanical power to the load
C To control the motor speed
D To connect to the external load

What is the primary cause of core losses in an induction motor?

A Eddy currents and hysteresis in the core
B Friction in the bearings
C Overloading of the motor
D Insufficient insulation

What is the effect of increasing the rotor resistance in a wound-rotor induction motor?

A The starting torque decreases
B The starting torque increases
C The motor operates at higher speeds
D The motor efficiency increases

What is the effect of under-excitation in a synchronous motor?

A It causes the motor to operate at a higher speed
B It causes the motor to operate with a lagging power factor
C It increases the motor’s efficiency
D It improves the motor’s torque

What happens when the load on an induction motor increases?

A The motor operates at synchronous speed
B The slip increases and the motor speed decreases slightly
C The motor speed increases
D The motor’s power factor improves

What is the purpose of a capacitor in a single-phase induction motor?

A To create a phase shift and improve starting torque
B To improve the motor’s power factor
C To reduce the motor’s power consumption
D To increase the motor’s speed

What is the main advantage of using squirrel-cage rotors in induction motors?

A Low maintenance and rugged construction
B High starting torque
C Increased speed control
D Improved power factor

What happens when the excitation of a synchronous motor is reduced?

A The power factor becomes lagging
B The motor becomes more efficient
C The motor loses synchronism
D The motor produces more torque

What is the effect of increasing the rotor resistance in a wound-rotor induction motor?

A The motor operates more efficiently at high speeds
B The starting torque increases
C The motor’s power factor improves
D The motor operates at synchronous speed

What is the effect of increasing the number of poles in a synchronous motor?

A The synchronous speed decreases
B The motor torque increases
C The power factor improves
D The rotor speed increases

What is the primary role of insulation materials in electric motors?

A To prevent electrical breakdown and improve durability
B To reduce mechanical wear
C To reduce the motor’s power factor
D To improve the motor’s cooling efficiency

What is the primary reason for using an autotransformer starter for large induction motors?

A To reduce the inrush current during startup
B To increase the starting torque
C To reduce the motor speed
D To increase the efficiency at full load