Automatic Voltage Regulation (AVR) in Power Systems
Automatic Voltage Regulation (AVR) is a crucial component in maintaining stable and reliable power system operation. Its primary function is to control the terminal voltage of synchronous generators by adjusting the excitation system. This ensures that the voltage delivered to the grid remains within acceptable limits, regardless of load variations or disturbances.
Why is AVR Necessary?
The voltage of a synchronous generator is directly influenced by its field excitation current. When the load on the generator changes, its terminal voltage tends to fluctuate. For instance, an increase in load typically causes the terminal voltage to drop, while a decrease in load can cause it to rise. These voltage variations can have detrimental effects on connected equipment, leading to inefficient operation, reduced lifespan, and even system instability. AVR systems counteract these changes by automatically adjusting the excitation current to keep the terminal voltage constant.
Think of AVR as the 'cruise control' for a generator's voltage, ensuring a smooth and consistent output.
Components of an AVR System
An AVR system typically consists of a sensor, a controller, and an exciter.
These three main components work in a closed-loop feedback system to maintain the generator's terminal voltage.
- Sensor (or Voltage Transformer - VT): This component measures the generator's terminal voltage and converts it into a signal that the controller can process.
- Controller (or Regulator): This is the 'brain' of the AVR. It compares the measured voltage with a desired setpoint (reference voltage). If there's a difference (error), it generates a corrective signal.
- Exciter: This is the 'muscle' of the AVR. It amplifies the controller's signal and uses it to adjust the DC field current supplied to the generator's field winding. Increasing field current boosts voltage; decreasing it reduces voltage.
How AVR Works: A Feedback Loop
The AVR operates on the principle of a negative feedback control system. Here's a simplified breakdown of the process:
Loading diagram...
- The generator's terminal voltage is continuously monitored by the sensor.
- The controller receives this measured voltage and compares it to the desired reference voltage.
- If the measured voltage is lower than the reference, the controller signals the exciter to increase the field current.
- An increased field current strengthens the magnetic field, causing the generator's output voltage to rise.
- If the measured voltage is higher than the reference, the controller signals the exciter to decrease the field current, reducing the output voltage.
- This process repeats continuously, ensuring the terminal voltage stays close to the setpoint.
Types of Exciters and AVR Systems
| Exciter Type | Description | Response Speed | Complexity |
|---|---|---|---|
| DC Exciters | Uses a DC generator (exciter) to supply DC to the main generator's field. | Slower | Relatively simple |
| AC Exciters (AC-AC) | Uses a small AC generator whose AC output is rectified to DC. | Faster | Moderate |
| Static Exciters | Uses solid-state electronic components (thyristors, diodes) for rectification and control, with no rotating parts. | Very Fast | Complex but reliable |
| Brushless Exciters | AC exciter mounted on the same shaft as the main generator; AC output is rectified by rotating diodes. | Fast | Moderate to complex |
AVR Performance and Tuning
The performance of an AVR system is characterized by its speed of response, steady-state accuracy, and stability. Tuning the controller parameters (like proportional, integral, and derivative gains) is crucial to achieve optimal performance. An improperly tuned AVR can lead to oscillations, slow voltage recovery, or even instability in the power system. Advanced AVRs may also incorporate power system stabilizer (PSS) functions to damp electromechanical oscillations.
The core of AVR operation is a feedback loop. The controller compares the actual terminal voltage (measured by the sensor) to the desired voltage (setpoint). If there's a difference (error), it adjusts the field current via the exciter. Increasing field current boosts voltage, and decreasing it reduces voltage. This continuous adjustment aims to minimize the error and maintain a constant terminal voltage.
Text-based content
Library pages focus on text content
Sensor, Controller, and Exciter.
To maintain a constant terminal voltage of a synchronous generator.
It increases the field excitation current to boost the terminal voltage.
Learning Resources
This blog post provides a clear explanation of AVR, its components, working principle, and types, making it a good introductory resource.
A technical overview from GE discussing the importance and functionality of AVR systems in power generation.
A YouTube video explaining the role of AVR in power system stability, often useful for visual learners.
Another educational video that breaks down the concept of AVR and its significance in power systems.
This page from BYJU'S covers various topics within Power System Protection and Control, which may include AVR as part of the syllabus context.
NPTEL lecture notes on excitation systems, which are integral to AVR, providing detailed technical information.
A general overview of Automatic Voltage Regulators, covering their applications beyond just power systems, but with relevant foundational information.
This portal often features articles on power system analysis and control, likely including detailed explanations of AVR concepts relevant to GATE.
A practical explanation of AVR, potentially showing how it functions in real-world scenarios or simulations.
This resource provides syllabus and notes for GATE Electrical Engineering, which will contextualize AVR within the broader power systems syllabus.