What is the primary cause of losses in an induction motor?
A Friction losses
B Core losses
C Rotor losses
D Stator losses
Core losses, which consist of eddy currents and hysteresis losses in the motor’s iron core, are a primary source of losses in induction motors. These losses convert electrical energy into heat, reducing motor efficiency.
What is the effect of increasing the load on the efficiency of an induction motor?
A Efficiency increases
B Efficiency fluctuates
C Efficiency decreases
D Efficiency remains constant
As the load increases on an induction motor, its efficiency generally increases because the motor operates closer to its rated capacity, reducing relative losses and making better use of the supplied energy.
What is the impact of a poor power factor on an induction motor?
A Reduced speed
B Increased torque
C Reduced voltage
D Increased current draw
A poor power factor in an induction motor means that more current is drawn to provide the necessary reactive power for the motor’s magnetic field. This leads to higher losses and reduced efficiency.
How can the power factor of an induction motor be improved?
A By increasing slip
B By increasing load
C By adding a capacitor
D By reducing supply voltage
Adding a capacitor helps improve the power factor by compensating for the inductive reactance of the motor, which reduces the phase difference between the voltage and current, thus improving efficiency.
What is the typical effect of higher slip in an induction motor?
A Decreased speed
B Increased current
C Decreased torque
D Increased efficiency
Higher slip means the rotor is moving slower than the synchronous speed, which causes the motor to draw more current to compensate for the increased load, potentially increasing losses and reducing efficiency.
What are the main losses in a synchronous motor?
A Copper losses
B Hysteresis and eddy current losses
C Rotor and friction losses
D Core and stator losses
The main losses in a synchronous motor are core losses, caused by the alternating magnetic field in the stator, and stator losses, due to the resistance in the stator windings. These losses reduce efficiency.
How does an increase in temperature affect the efficiency of an induction motor?
A Decreases efficiency
B No effect
C Increases torque
D Increases efficiency
As the temperature increases, the resistance of the motor windings increases, which leads to more energy being lost as heat. This reduces the overall efficiency of the motor.
What is the primary factor that affects the power factor of an induction motor?
A Slip
B Load
C Voltage
D Speed
The power factor of an induction motor is primarily affected by the load. A lightly loaded motor has a low power factor, while a heavily loaded motor has a higher power factor, due to better current utilization.
What is the effect of running an induction motor under no-load conditions?
A Increased slip
B Low current
C Low power factor
D High efficiency
When running under no-load conditions, an induction motor draws high reactive power and exhibits a low power factor. The motor does not utilize the power effectively to do work, leading to lower efficiency.
What type of losses are caused by the resistance of the rotor windings in an induction motor?
A Copper losses
B Iron losses
C Core losses
D Friction losses
Copper losses occur due to the resistance in the rotor and stator windings. These losses are proportional to the square of the current and are a major source of energy dissipation in the motor.
Which of the following increases as the efficiency of an induction motor improves?
A Starting torque
B Core losses
C Power factor
D Slip
As the efficiency of an induction motor improves, the power factor also tends to improve. This is because the motor is operating closer to its rated load, reducing the phase difference between voltage and current.
What type of motor is more susceptible to losses due to harmonics?
A Universal motor
B Induction motor
C Permanent magnet motor
D Synchronous motor
Induction motors are more susceptible to losses due to harmonics because the non-sinusoidal nature of the power supply causes additional losses, resulting in higher core losses and heating, which reduces motor efficiency.
What happens to the efficiency of an induction motor when the load is under-loaded?
A Efficiency decreases
B No effect on efficiency
C Speed decreases
D Efficiency increases
Under-loaded induction motors operate less efficiently because a significant portion of the power is wasted in overcoming the motor’s inherent losses, even though the motor is not doing much useful work.
Which type of loss occurs in the iron core of an induction motor?
A Windage loss
B Copper loss
C Friction loss
D Core loss
Core loss occurs in the motor’s iron core due to the alternating magnetic field. It consists of eddy current losses and hysteresis losses, which are a significant factor in the total energy loss in the motor.
How does the efficiency of a synchronous motor compare to an induction motor?
A Same efficiency
B Higher efficiency
C Lower efficiency
D Depends on load
Synchronous motors generally have higher efficiency than induction motors because they operate at a constant speed, and their power factor can be adjusted. This leads to better overall performance and reduced energy losses.