What is the primary role of stator windings in an alternator?
A Supply Field Current
B Generate Voltage
C Control Frequency
D Rotate the Rotor
The stator windings are responsible for generating the electrical voltage when the rotor rotates within the magnetic field. The induced voltage is the alternating current produced by the alternator.
What is the key feature of a salient pole rotor in an alternator?
A Protruding Poles
B High Inertia
C Smooth Surface
D Low Efficiency
A salient pole rotor features poles that protrude from the rotor’s surface. This design is typically used in low-speed alternators, such as hydroelectric generators, due to its efficient magnetic field creation.
What is the effect of high slip in an induction generator?
A Improved Power Factor
B Increased Efficiency
C Reduced Speed
D Decreased Voltage
High slip in an induction generator leads to a greater difference between the synchronous speed and the actual rotor speed. This can cause a drop in the generated voltage, reducing the generator’s efficiency.
What does the exciter system in an alternator provide?
A Load Sharing
B Mechanical Power
C Field Current
D Rotor Cooling
The exciter system provides the necessary field current to the rotor, enabling it to create the magnetic field needed for inducing voltage in the stator windings, which is crucial for power generation.
Which of the following is typically used to control the voltage in an alternator?
A Excitation System
B Power Factor
C Governor System
D Slip Ring
The excitation system controls the field current to the rotor, regulating the alternator’s output voltage. By adjusting the excitation, it ensures that the voltage remains stable under varying load conditions.
In an induction generator, how is power generated?
A Grid Synchronization
B External Supply
C Rotor Movement
D Stator Magnetic Field
In an induction generator, mechanical energy from the rotor’s movement is converted into electrical energy. This is achieved by the interaction between the rotor and the stator’s magnetic field, without requiring an external excitation source.
How is the synchronous speed of an alternator calculated?
A Voltage × Rotor Speed
B Rotor Speed × Power Factor
C 120 × Frequency / Poles
D Frequency × Number of Poles
The synchronous speed of an alternator is calculated using the formula 120 times the frequency divided by the number of poles. This determines the constant speed required for synchronization with the grid.
What is the primary function of the rotor in an alternator?
A Maintain Voltage
B Create Magnetic Field
C Generate Power
D Control Speed
The rotor’s primary function in an alternator is to create a rotating magnetic field. This magnetic field induces a current in the stator windings, producing alternating current for electrical power generation.
What is a key advantage of using a brushless excitation system in alternators?
A Increased Slip
B Higher Voltage
C Less Maintenance
D Reduced Cost
Brushless excitation systems are advantageous because they eliminate the need for brushes and slip rings, which reduces maintenance requirements. These systems are more durable and reliable, leading to lower operational costs.
In a three-phase alternator, how is the power output typically balanced?
A Load Sharing
B Frequency Control
C Parallel Operation
D Voltage Regulation
In a three-phase alternator system, load sharing is essential for balancing the power output. Multiple alternators can work in parallel to distribute the load, ensuring each unit operates within its capacity and efficiently generates power.
Which type of rotor is used in high-speed alternators?
A Salient Pole
B Permanent Magnet
C Squirrel Cage
D Cylindrical
High-speed alternators typically use cylindrical rotors. These rotors have a smooth surface and are designed for high rotational speeds, making them suitable for large power plants and industrial applications.
How is an induction generator different from a synchronous generator?
A Higher Efficiency
B Fixed Frequency
C Operates at Variable Speed
D Requires Excitation
Unlike synchronous generators, which operate at a constant speed, induction generators can operate at variable speeds. This flexibility is useful in renewable energy systems, such as wind power, where the mechanical input speed varies.
What does the term “slip” refer to in an induction generator?
A Frequency Variation
B Rotor Speed Difference
C Current Deviation
D Voltage Fluctuation
Slip refers to the difference between the synchronous speed and the actual rotor speed in an induction generator. This difference is necessary for the generation of electrical power, and it is typically small under normal operating conditions.
What is the main function of the governor in an alternator system?
A Protect from Faults
B Control Excitation
C Maintain Voltage
D Regulate Speed
The governor system in an alternator regulates the speed of the prime mover (such as a turbine or engine) that drives the alternator. It ensures that the rotor speed is constant and synchronized with the grid frequency.
What is a common application of a single-phase alternator?
A Small Appliances
B Industrial Systems
C Wind Turbines
D Power Plants
Single-phase alternators are commonly used in small appliances and residential applications because they are cost-effective for low-power needs. They are simpler in design but suitable for small-scale power generation.