What is the purpose of the excitation system in a synchronous motor?
A Increase efficiency
B Provide rotor magnetic field
C Control rotor speed
D Supply power
The excitation system in a synchronous motor provides direct current (DC) to the rotor, creating a magnetic field that interacts with the stator’s rotating magnetic field, enabling the motor to run at synchronous speed.
What is the effect of improper voltage regulation in a synchronous motor?
A Increased power factor
B Constant speed operation
C Speed instability
D Reduced load sharing
Improper voltage regulation can lead to uneven load sharing in parallel operation of synchronous motors. This can cause one motor to carry more load than others, affecting efficiency and stability.
How does the excitation system affect the voltage regulation of a synchronous generator?
A It adjusts the output voltage
B It reduces core losses
C It increases torque
D It stabilizes the speed
The excitation system in a synchronous generator controls the field current, which in turn adjusts the output voltage. Proper excitation ensures that the generator maintains a constant voltage despite varying loads.
What happens when the excitation of a synchronous motor is reduced?
A Efficiency improves
B Speed increases
C The motor becomes unstable
D The motor operates at sub-synchronous speed
Reducing the excitation of a synchronous motor causes a loss of synchronism, making the motor unstable. The rotor no longer matches the stator’s magnetic field, and the motor will lose synchronization.
In which operation is the voltage regulation of a synchronous motor most critical?
A At startup
B Under full load
C At no load
D At low speed
Voltage regulation is most critical under full load conditions because the motor must adjust to load changes and maintain a stable output voltage. Proper regulation ensures the motor operates efficiently under varying loads.
What is the relationship between excitation and power factor in synchronous motors?
A Higher excitation increases power factor
B Excitation has no effect on power factor
C Lower excitation increases power factor
D Higher excitation decreases power factor
Higher excitation in synchronous motors increases the motor’s ability to generate a stronger magnetic field, improving its power factor. Proper excitation allows the motor to operate closer to unity power factor.
How is the voltage regulation of a synchronous generator typically measured?
A By the load angle
B By the speed of the rotor
C By the armature current
D By the change in load
Voltage regulation of a synchronous generator is measured by the change in output voltage when the load varies. A stable generator will maintain nearly constant voltage despite changes in the load.
What is the effect of under-excitation in a synchronous motor?
A Increases load capacity
B Reduces rotor losses
C Decreases power factor
D Improves efficiency
Under-excitation in a synchronous motor reduces the motor’s magnetic field strength, causing the motor to operate with a lower power factor. This leads to less efficient operation and poor voltage regulation.
What is the primary cause of voltage fluctuation in a synchronous generator under varying loads?
A Rotor speed variation
B Insufficient excitation
C Incorrect slip setting
D Over-excitation
Insufficient excitation in a synchronous generator causes voltage fluctuations under varying loads. Without enough excitation, the motor cannot maintain the necessary magnetic field strength, resulting in unstable voltage output.
What happens when a synchronous motor is overloaded?
A It increases power factor
B It reduces current
C It speeds up
D It loses synchronism
When a synchronous motor is overloaded, it cannot maintain synchronization with the stator’s rotating magnetic field. As a result, it falls out of synchronism, causing the motor to stop running efficiently.
How does excitation affect the stability of a synchronous generator?
A Higher excitation improves stability
B Excitation does not affect stability
C Lower excitation improves stability
D Excitation decreases stability
Higher excitation increases the strength of the magnetic field in the rotor, which improves the stability of the synchronous generator. This helps maintain voltage regulation and improves load sharing under varying loads.
What is the primary role of the excitation system in a synchronous machine?
A Increase efficiency
B Maintain voltage stability
C Control rotor speed
D Adjust torque output
The excitation system in a synchronous machine controls the rotor’s magnetic field strength, ensuring that the machine maintains a stable voltage. It is crucial for regulating the machine’s output voltage under different load conditions.
What happens if a synchronous motor runs at an excessively high excitation?
A It draws excessive current
B It stabilizes load sharing
C It runs at higher speed
D It improves voltage regulation
Excessive excitation in a synchronous motor can lead to higher-than-necessary current draw. This increases losses, reduces efficiency, and may cause the motor to overheat, resulting in operational instability.
What is the primary characteristic of the voltage regulation of a synchronous generator?
A It is constant under varying load
B It increases with load
C It depends on excitation level
D It varies with speed
Voltage regulation in a synchronous generator is highly dependent on the excitation level. Higher excitation leads to better regulation by maintaining stable voltage output as the load changes.
What would happen to the power factor of a synchronous motor with over-excitation?
A Power factor worsens
B Power factor improves
C Power factor remains constant
D Power factor becomes zero
Over-excitation in a synchronous motor increases the motor’s ability to generate a stronger magnetic field, improving the motor’s power factor. This results in a higher percentage of the supplied power being converted into useful work.