Short Answer:
Automatic Voltage Regulators (AVRs) play a very important role in maintaining the stability of a power system, especially in regulating the voltage at generator terminals. AVRs automatically adjust the excitation of a synchronous generator to keep the output voltage constant during normal and disturbed conditions.
By quickly responding to voltage changes, AVRs help in maintaining voltage stability, improving reactive power sharing, and enhancing the transient and small signal stability of the system. This ensures that the generator remains synchronized and the overall system continues to operate smoothly and reliably.
Detailed Explanation:
Role of Automatic Voltage Regulators (AVR) in stability
An Automatic Voltage Regulator (AVR) is a control device attached to a synchronous generator. Its main function is to automatically control the generator’s terminal voltage by adjusting its field current. In modern power systems, AVRs are essential components that support system stability, ensure voltage quality, and help in maintaining a balanced operation of the network.
AVRs continuously monitor the output voltage of the generator and compare it with a predefined reference value. If there is any deviation, the AVR adjusts the excitation of the generator to bring the voltage back to the desired level.
How AVR supports different types of stability
- Voltage stability:
- AVRs directly help in maintaining voltage levels within acceptable limits, especially during sudden changes in load.
- When load increases or decreases, reactive power demand changes. The AVR adjusts excitation to supply or absorb reactive power, keeping the voltage stable.
- AVRs prevent voltage collapse, which is a common issue in weak or heavily loaded systems.
- Transient stability:
- During a fault or sudden disturbance, rotor angle deviations occur.
- A fast-acting AVR increases excitation quickly, which increases generator voltage and helps in supplying more reactive power.
- This boosts the generator’s electrical power output, helping the rotor to decelerate faster and regain synchronism.
- Thus, AVRs improve the system’s ability to withstand large disturbances and avoid instability.
- Small signal stability:
- AVRs help control low-frequency oscillations between generators due to small disturbances.
- By adjusting excitation quickly, AVRs damp out these oscillations, preventing them from growing uncontrollably.
- The addition of Power System Stabilizers (PSS) with AVRs further improves damping and enhances small signal stability.
Additional functions and benefits
- Reactive power sharing: AVRs maintain proper reactive power balance among parallel generators.
- Improved voltage profile: AVRs help in achieving a flat voltage profile across buses in a system.
- Support during load variations: In industries or dynamic load environments, AVRs ensure consistent performance.
- Automatic response: They eliminate the need for manual adjustment of excitation, improving system reliability.
Modern enhancements
Modern AVRs are equipped with:
- Digital controllers
- Voltage and power factor settings
- Protection features (over/under voltage, over excitation)
- Integration with SCADA and automation systems
They allow faster and more accurate control, making them essential in both conventional and smart grid operations.
Conclusion:
The role of Automatic Voltage Regulators (AVRs) in power system stability is critical. They maintain voltage levels, improve generator response during faults, and help keep the system synchronized and stable. AVRs enhance voltage, transient, and small signal stability, making them a key part of safe and efficient power system operation.