Governors are crucial for maintaining power system stability. They regulate turbine speed and match generator output to electrical demand, keeping frequency within acceptable limits. Different types of governors, from mechanical-hydraulic to electronic, offer varying levels of precision and responsiveness.
Understanding governor control principles is essential for power system engineers. Negative feedback control and droop characteristics allow governors to respond to frequency deviations and share loads between generators. This knowledge is fundamental for designing and operating stable power systems.
Governor Types and Applications
Main Types of Governors
Top images from around the web for Main Types of Governors
aircraft design - What are Electro Hydraulic Servo Valves and Solenoid Operated Valves ... View original
Mechanical-hydraulic governors rely on mechanical and hydraulic components to control the speed of the turbine and are commonly used in hydroelectric power plants and small to medium-sized thermal power plants
Electro-hydraulic governors combine electronic control systems with hydraulic actuators, offer improved response times and accuracy compared to purely mechanical governors, and are used in larger thermal power plants
Electronic governors, also known as digital governors, utilize microprocessors and digital control algorithms, offer high precision, flexibility, and advanced control features, and are used in modern power plants of various types and sizes (gas turbines, combined cycle plants)
Applications of Governor Types
Mechanical-hydraulic governors are suited for hydroelectric power plants due to their ability to handle the large inertia of water turbines and the need for precise control of water flow through the wicket gates
Electro-hydraulic governors are employed in larger thermal power plants (coal-fired, nuclear) where the increased accuracy and faster response times provided by the electronic control components are beneficial for maintaining stable operation
Electronic governors are widely used in modern power plants, including gas turbines and combined cycle plants, as they offer advanced control capabilities, such as PID control, overspeed protection, and integration with plant control systems (distributed control systems, SCADA)
Governor Control Principles
Frequency Regulation and Load Matching
Governors maintain the frequency of a power system within acceptable limits (typically ±0.5 Hz) by controlling the speed of the prime mover (turbine) in response to load changes
The primary function of a governor is to adjust the mechanical power input to the generator to match the electrical power output, ensuring that the system frequency remains at the nominal value (50 Hz or 60 Hz)
Governors continuously monitor the system frequency and compare it with the reference frequency, triggering corrective actions to adjust the prime mover's speed when deviations occur
Negative Feedback Control and Droop Characteristic
Governors operate based on the principle of negative feedback control, where the system frequency is compared with the reference frequency, and any deviation results in a corrective action by the governor to adjust the prime mover's speed
The governor's control action is proportional to the frequency deviation, with larger deviations resulting in more significant adjustments of the prime mover's speed, helping to stabilize the system frequency
Governors have a that allows multiple generators to share the load proportionally, with the droop setting determining the percentage change in frequency that causes a 100% change in the generator's output (e.g., a 5% droop means a 5% change in frequency results in a 100% change in generator output)
Mechanical-Hydraulic Governors
Key Components
Speed-sensing device (flyball mechanism) detects changes in the turbine's speed, with the flyballs moving outward due to centrifugal force as the speed increases, causing a displacement in the linkage system
Hydraulic amplifier converts the small mechanical motion of the pilot valve into a larger hydraulic force, which is applied to the servomotor
Pilot valve controls the flow of oil in the hydraulic amplifier based on the displacement of the linkage system caused by the speed-sensing device
Servomotor actuates the control valves of the prime mover (steam admission valves in a steam turbine or wicket gates in a hydro turbine) in response to the amplified hydraulic force from the hydraulic amplifier
Linkage system connects the servomotor to the prime mover's control valves and provides a mechanical feedback from the servomotor to the pilot valve, ensuring stable operation and preventing overshooting or hunting of the governor's response
Operation Principles
The speed-sensing device detects changes in the turbine's speed, causing a displacement in the linkage system that affects the position of the pilot valve
The pilot valve controls the flow of oil in the hydraulic amplifier, which converts the small mechanical motion into a larger hydraulic force applied to the servomotor
The servomotor actuates the control valves of the prime mover, regulating the flow of the working fluid (steam or water) to control its speed
The linkage system provides a mechanical feedback from the servomotor to the pilot valve, ensuring stable operation and preventing overshooting or hunting of the governor's response
Electronic vs Mechanical Governors
Advantages of Electronic Governors
Higher accuracy in maintaining system frequency due to the use of digital control techniques and advanced control algorithms (PID control)
Faster response times to load changes and frequency deviations compared to mechanical governors, improving system stability
Greater flexibility in control algorithms and settings, allowing for customization and optimization of governor performance based on specific plant requirements
Incorporation of additional control functions, such as overspeed protection, load limiters, and (AGC), enhancing overall system stability and reliability
Reduced maintenance requirements and increased system lifespan due to the absence of mechanical wear and tear
Limitations of Electronic Governors
Higher initial costs compared to mechanical governors due to the use of advanced electronic components and control software
Increased complexity in design, implementation, and troubleshooting, requiring specialized knowledge and skills for maintenance and repair
Potential vulnerability to electromagnetic interference (EMI) and cybersecurity threats, necessitating proper shielding, grounding, and security measures to ensure reliable operation
Dependence on the quality and reliability of electronic components and control software, requiring thorough design, testing, and maintenance to prevent failures and ensure long-term performance