6.1 Governor types and control principles
4 min read•august 1, 2024
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
Is this image relevant?
Control theory - Wikipedia View original
Is this image relevant?
aircraft design - What are Electro Hydraulic Servo Valves and Solenoid Operated Valves ... View original
Is this image relevant?
Control theory - Wikipedia View original
Is this image relevant?
1 of 2
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
Is this image relevant?
Control theory - Wikipedia View original
Is this image relevant?
aircraft design - What are Electro Hydraulic Servo Valves and Solenoid Operated Valves ... View original
Is this image relevant?
Control theory - Wikipedia View original
Is this image relevant?
1 of 2
- 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
Key Terms to Review (20)
Automatic Generation Control: Automatic Generation Control (AGC) is a system used in power generation to maintain the balance between electrical supply and demand by automatically adjusting the output of generators. This technology plays a critical role in ensuring system frequency stability, supporting overall power system stability, and achieving control objectives that align with operational requirements.
Bessey’s Model: Bessey’s Model is a theoretical framework used to analyze the dynamics of governor systems in power generation, particularly focusing on how they regulate the output of generators in response to changes in load. This model simplifies the complex interactions between mechanical components and electrical systems to provide a clearer understanding of governor behavior under various conditions. By representing these interactions mathematically, it aids in improving stability and control in power systems.
Droop Characteristic: Droop characteristic refers to a control strategy used in power systems, specifically in the context of generator and governor operations, that allows generators to share the load based on their frequency response. This characteristic is crucial for ensuring stability in a grid by providing a natural response to frequency changes, enabling generators to reduce their output when frequency increases and increase output when frequency decreases, thus helping maintain system equilibrium.
Dynamic response: Dynamic response refers to how a power system reacts over time to changes, such as disturbances or control actions. It encompasses the transient and steady-state behavior of the system as it adjusts to new conditions, influenced by various control mechanisms and system characteristics. Understanding dynamic response is crucial for evaluating system stability, performance, and control efficiency in various scenarios.
Electro-hydraulic governor: An electro-hydraulic governor is a device that automatically controls the output of a generator or turbine by adjusting the flow of hydraulic fluid based on electrical signals. This type of governor utilizes both electrical and hydraulic components to maintain the desired speed and load of the machine, ensuring stable and efficient operation under varying conditions.
Electronic governor: An electronic governor is a digital control system designed to regulate the speed and output of generators and turbines in power systems. This technology enhances precision and response time in maintaining the desired frequency and load balance, crucial for overall system stability. Electronic governors utilize advanced algorithms and real-time data to make adjustments that help ensure optimal performance across various operating conditions.
Frequency regulation: Frequency regulation is the process of maintaining the balance between electricity supply and demand to ensure that the system frequency remains within a specified range, typically around 60 Hz in North America. This process is critical for system stability and is influenced by various control mechanisms, including automatic generation control and energy management systems. Effective frequency regulation can involve different technologies and strategies that help to mitigate fluctuations in supply and demand.
Hydraulic governor: A hydraulic governor is a device used to regulate the speed and output of a hydraulic system, typically in power generation applications, by adjusting the flow of fluid based on the demand for power. This device plays a crucial role in maintaining system stability by ensuring that the hydraulic turbine operates within desired speed limits and responds efficiently to fluctuations in load. The hydraulic governor's operation is largely dependent on principles of fluid mechanics and control theory, making it essential for effective power system management.
IEEE Standard Models: IEEE Standard Models refer to a set of established guidelines and frameworks used to represent dynamic behaviors of power system components, particularly in the context of stability analysis and control. These models help in simulating the performance of generators, governors, exciters, and other key equipment under various operating conditions, ensuring consistent and accurate analysis across different studies and applications.
Integral Control: Integral control is a fundamental component of feedback control systems that continuously adjusts the control output based on the accumulated error over time, ensuring that any steady-state error is eliminated. This type of control is crucial for maintaining system stability and performance, especially in systems where precise regulation is needed. It connects directly to concepts like governor functions, speed-droop characteristics for load sharing, and coordinated controls among different system components.
Linear modeling: Linear modeling is a mathematical technique used to represent complex relationships between variables through linear equations, typically in the form of a straight line. This method simplifies analysis by assuming that changes in one variable result in proportional changes in another, making it particularly useful for control systems, where precise adjustments are necessary for stability and performance.
Load Frequency Control: Load frequency control is a crucial process in power systems that manages the balance between electricity supply and demand by regulating the system frequency. This control mechanism ensures that deviations from the nominal frequency are corrected through automatic adjustments in generation, helping to maintain system stability and reliability. Proper load frequency control is essential for interconnected power systems, where the frequency is influenced by multiple generators and loads.
Load sharing: Load sharing refers to the practice of distributing the electrical load among multiple generators or power sources to optimize performance and ensure stability within a power system. This concept is crucial for maintaining balance in generation and consumption, preventing overloads, and enhancing overall system reliability. By implementing effective load sharing techniques, operators can improve efficiency, prolong equipment life, and provide a stable power supply to consumers.
Nonlinear dynamics: Nonlinear dynamics refers to the behavior of systems governed by nonlinear equations, where small changes in initial conditions can lead to vastly different outcomes. This concept is crucial in understanding complex systems, such as power systems, where feedback loops and interactions can create unpredictable and sometimes chaotic behavior. Nonlinear dynamics is especially relevant when analyzing control strategies for governors that regulate power generation and maintain system stability.
Proportional Control: Proportional control is a control strategy that provides an output response that is directly proportional to the error signal, which is the difference between a desired setpoint and the actual output. This method is foundational in feedback control systems, allowing for effective regulation of processes by adjusting system variables to maintain stability and performance.
Response Time: Response time refers to the time it takes for a system to react to an input or disturbance. In power systems, this concept is crucial as it affects how quickly control systems, like excitation systems and governors, can adjust to changes in load or generation. Faster response times are essential for maintaining stability and ensuring reliable operation in various system conditions.
Secondary Control: Secondary control refers to the regulatory mechanisms in power systems that manage the balance of supply and demand over a longer time frame, typically addressing frequency and voltage issues once primary control has stabilized the system. It plays a critical role in ensuring that the system remains stable by coordinating adjustments from multiple generators, allowing for optimal operation and resource allocation. This kind of control is essential for maintaining overall system integrity, especially when integrating renewable energy sources and managing distributed generation.
Settling Time: Settling time is the duration required for a system's response to stabilize within a specified tolerance band around the final value after a disturbance or change in input. This concept is crucial for assessing how quickly control systems can react to changes, ensuring that parameters like frequency and power output return to acceptable levels. It plays a significant role in evaluating the effectiveness of different governor types, the design of small-signal stability controls, and the overall performance of Automatic Generation Control systems.
Speed governor: A speed governor is a device used in power systems to automatically control the speed of a generator or turbine by regulating its fuel input. This control mechanism ensures that the generator operates within desired speed limits and maintains stability in response to varying loads or disturbances in the system. By adjusting the fuel supply, the speed governor plays a critical role in ensuring reliable power generation and grid stability.
Tertiary control: Tertiary control refers to the overarching management and optimization of a power system, focusing on long-term stability, resource allocation, and economic efficiency. It complements primary and secondary controls by ensuring that the system operates within its desired parameters over extended periods while balancing supply and demand in an effective manner. Tertiary control also plays a vital role in coordinating various generation sources and storage options, especially in modern systems incorporating renewable energy sources and microgrids.