14.1 FACTS device types and operating principles
4 min read•august 1, 2024
FACTS devices are power electronic systems that enhance AC transmission network control and capacity. They include SVCs, STATCOMs, TCSCs, SSSCs, and UPFCs, each serving specific roles in voltage regulation, reactive power , and .
These devices operate on shunt or series compensation principles, using thyristor-controlled components or voltage-sourced converters. They offer benefits like improved stability and efficiency, but face challenges such as high costs and control complexity.
FACTS Devices and Their Roles
Main Types of FACTS Devices
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- Flexible AC Transmission Systems (FACTS) are power electronic-based devices used to enhance controllability and increase power transfer capability of AC transmission networks
- The main types of FACTS devices include:
- Static VAR Compensators (SVCs)
- Static Synchronous Compensators (STATCOMs)
- Thyristor-Controlled Series Capacitors (TCSCs)
- Static Synchronous Series Compensators (SSSCs)
- Unified Power Flow Controllers (UPFCs)
Applications of FACTS Devices
- SVCs and STATCOMs are shunt-connected devices used for reactive power compensation and voltage control
- They help maintain stable voltage levels and improve voltage stability (power system stability)
- TCSCs and SSSCs are series-connected devices used for impedance compensation and power flow control
- They regulate power flow by modifying the effective impedance of transmission lines (power transfer capability)
- UPFCs are a combination of shunt and series devices, providing both voltage regulation and power flow control capabilities
- They offer comprehensive control over voltage and power flow in transmission networks (flexibility and controllability)
Operating Principles of FACTS Devices
Shunt Compensation Devices
- SVCs consist of thyristor-controlled reactors (TCRs) and thyristor-switched capacitors (TSCs) connected in parallel
- They provide stepwise reactive power compensation by adjusting the firing angles of the thyristors
- SVCs can rapidly adjust reactive power output to maintain stable voltage levels (dynamic response)
- STATCOMs use voltage-sourced converters (VSCs) to generate or absorb reactive power
- They provide continuous and rapid reactive power compensation without the need for large capacitor banks or reactors
- STATCOMs have faster response times and better dynamic performance compared to SVCs ()
Series Compensation Devices
- TCSCs use thyristor-controlled series capacitors to provide continuous control of the line impedance
- By varying the firing angle of the thyristors, TCSCs can increase or decrease the effective series compensation
- TCSCs can regulate power flow, improve transient stability, and mitigate subsynchronous resonance (SSR) issues (power system oscillations)
- SSSCs employ VSCs connected in series with the transmission line
- They can inject a voltage with controllable magnitude and phase angle to regulate the power flow and improve system stability
- SSSCs provide fast and dynamic control over power flow, enhancing power transfer capability and system stability (power system dynamics)
Unified Power Flow Controllers (UPFCs)
- UPFCs consist of two VSCs coupled through a common DC link
- The shunt VSC regulates the bus voltage, while the series VSC controls the power flow by injecting a voltage with controllable magnitude and phase angle
- UPFCs offer independent control over both voltage and power flow, providing comprehensive control capabilities (power system control)
Benefits and Limitations of FACTS Devices
Benefits of FACTS Devices
- Improved voltage stability by regulating voltage levels and providing reactive power support (voltage control)
- Enhanced power transfer capability by optimizing power flow and reducing transmission congestion (power system operation)
- Increased through fast and dynamic control, allowing quick response to changes in load or generation (power system reliability)
- Better control over power flow in the network, enabling efficient utilization of transmission assets (power system optimization)
- Mitigation of transmission losses and improvement in overall power system efficiency (energy efficiency)
Limitations of FACTS Devices
- High installation and maintenance costs associated with FACTS devices (economic considerations)
- Complexity in control and coordination of multiple FACTS devices in a network (control system design)
- Potential harmonic distortion introduced by the power electronic converters used in FACTS devices ( issues)
- Effectiveness of FACTS devices depends on proper placement and sizing, requiring detailed system studies and optimization techniques (system planning and analysis)
Series vs Shunt Compensation Techniques
Series Compensation Techniques
- Series compensation devices, such as TCSCs and SSSCs, are connected in series with the transmission line
- They directly influence the power flow by modifying the line impedance (power flow control)
- Series compensation devices can regulate the power flow, improve transient stability, and mitigate subsynchronous resonance (SSR) issues
- They are effective in controlling power flow and improving power transfer capability (power system stability)
Shunt Compensation Techniques
- Shunt compensation devices, such as SVCs and STATCOMs, are connected in parallel with the transmission line
- They primarily focus on reactive power compensation and voltage control (voltage regulation)
- Shunt compensation devices can regulate the bus voltage, improve voltage stability, and provide dynamic reactive power support to the system
- They are suitable for maintaining stable voltage levels and enhancing voltage stability (power system reliability)
Comparison of Series and Shunt Compensation
- Series compensation devices are more effective in controlling the power flow and improving the power transfer capability
- They directly influence the power flow by modifying the line impedance (power system control)
- Shunt compensation devices are more suitable for voltage regulation and reactive power management
- They provide reactive power support and help maintain stable voltage levels (voltage stability)
- In some cases, a combination of series and shunt compensation techniques, such as UPFCs, can provide comprehensive control over both power flow and voltage in the transmission network
- UPFCs offer independent control over voltage and power flow, enhancing overall power system performance (power system optimization)
Key Terms to Review (19)
Compensation: Compensation refers to the process of adjusting the performance of power systems to enhance stability and improve control. This adjustment can involve modifying voltage levels, phase angles, or power flows to maintain system reliability and efficiency. It is crucial for managing the dynamic behavior of electrical grids, especially during disturbances or fluctuations.
Dynamic stability: Dynamic stability refers to the ability of a power system to maintain equilibrium during and after disturbances, ensuring that the system can return to a stable operating condition. This concept is crucial for understanding how power systems react to changes, such as faults or load variations, and is closely linked to control objectives, power flow formulations, and the response of the system's components over time.
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.
Grid integration: Grid integration refers to the process of connecting various energy sources, such as renewable and conventional generation, to the electrical grid in a way that ensures reliability, stability, and efficiency. This involves balancing supply and demand, managing power flows, and utilizing advanced technologies to maintain grid performance, especially as the share of variable renewable resources like wind and solar increases.
H. Akagi: H. Akagi is a prominent figure in the development of Flexible AC Transmission Systems (FACTS) technologies, which are crucial for enhancing the reliability and efficiency of power systems. His work primarily focuses on the introduction and advancement of various FACTS devices that improve power flow control and system stability. Akagi's contributions have played a significant role in the integration of renewable energy sources and the optimization of existing electrical grids.
IEEE Standards: IEEE standards are technical specifications and guidelines developed by the Institute of Electrical and Electronics Engineers to ensure quality, reliability, and interoperability in electrical and electronic systems. These standards cover various aspects of power systems, promoting safety, efficiency, and stability across multiple applications.
Modulation: Modulation refers to the process of varying a property of a signal in order to encode information, commonly seen in the context of communication systems. In power systems, especially concerning FACTS devices, modulation is crucial for controlling the flow of electrical power by adjusting parameters such as voltage or current to achieve desired stability and performance. This technique is essential for enhancing system reliability and improving response to dynamic conditions.
Power flow control: Power flow control refers to the management and regulation of electrical power transfer within a power system to maintain stability and optimize performance. This involves adjusting the flow of electricity in transmission lines and ensuring that the system operates within safe limits, which is crucial for maintaining reliability, efficiency, and the overall balance between supply and demand.
Power Quality: Power quality refers to the characteristics of electrical power that affect the performance of electrical equipment. It encompasses voltage stability, frequency, and waveform distortion, which can significantly impact the reliability and efficiency of power systems, especially as renewable energy sources become more prevalent. Maintaining good power quality is essential for ensuring system stability, minimizing equipment damage, and enhancing overall operational efficiency in modern power networks.
Reactive power control: Reactive power control is the management of reactive power in electrical systems to maintain voltage stability and optimize the performance of power systems. This control is crucial for ensuring that electrical equipment operates efficiently and effectively, particularly in environments with variable loads and renewable energy sources. By regulating reactive power, systems can enhance stability, reduce losses, and improve the quality of power delivered to consumers.
Renewable energy support: Renewable energy support refers to the various mechanisms and strategies employed to promote the development and integration of renewable energy sources into the power system. This support is essential for enhancing grid reliability and stability, especially as renewable sources like wind and solar are variable in nature. By using technologies such as FACTS devices, which help manage power flow and voltage stability, renewable energy support ensures that these cleaner energy sources can be effectively utilized in a modern power grid.
SSSC: The SSSC, or Static Synchronous Series Compensator, is a type of FACTS device that enhances the transmission capacity and stability of power systems by dynamically controlling the reactive power flow. It operates by injecting or absorbing reactive power in series with the transmission line, which helps to regulate voltage levels and mitigate issues such as line overloads and stability problems.
STATCOM: A STATCOM, or Static Synchronous Compensator, is a power electronic device used to regulate voltage in electrical power systems by providing reactive power compensation. It enhances the stability of the power grid by quickly injecting or absorbing reactive power in response to fluctuations in load and generation. By maintaining voltage levels and improving system reliability, STATCOMs play a crucial role in modern power system operation and control.
SVC: SVC stands for Static Var Compensator, a type of FACTS (Flexible AC Transmission Systems) device that is used to regulate voltage levels in electrical power systems by providing dynamic reactive power compensation. SVCs help stabilize the system by automatically adjusting reactive power flow in response to changes in load or system conditions, enhancing power quality and reliability.
System reliability: System reliability refers to the ability of a power system to consistently perform its intended function under predetermined conditions without failure. It emphasizes the importance of maintaining continuous and stable electricity supply, minimizing outages, and ensuring that all components of the system work harmoniously together. High reliability is crucial for meeting consumer demands and supporting the overall stability of the grid.
TCSC: The Thyristor Controlled Series Capacitor (TCSC) is a type of Flexible AC Transmission System (FACTS) device used to enhance the controllability and stability of power systems by providing dynamic reactive power compensation. It works by inserting a variable capacitive reactance into the transmission line, allowing for better control over power flow and voltage stability. TCSCs play a significant role in improving the overall reliability and efficiency of electrical grids, particularly in managing the challenges associated with fluctuating loads and generation.
Transient Stability: Transient stability refers to the ability of a power system to maintain synchronism when subjected to a disturbance, such as a fault or sudden change in load. It focuses on the immediate response of the system after such disturbances and how well it can return to a stable operating condition. This concept is crucial in understanding system behavior during and after transient events, particularly in multi-machine environments.
UPFC: The Unified Power Flow Controller (UPFC) is a sophisticated FACTS device that enhances the controllability and stability of power systems by simultaneously regulating voltage, current, and power flows in transmission lines. This capability is critical for optimizing the performance of electrical networks and preventing issues related to stability and reliability in power distribution.
Voltage Source Converter: A voltage source converter (VSC) is a power electronic device that converts electrical energy from one form to another, using a controllable voltage source to produce alternating current (AC) from direct current (DC) or vice versa. VSCs are key components in Flexible AC Transmission Systems (FACTS), enabling control of power flow, voltage support, and dynamic stability in power systems. They utilize power semiconductor devices to regulate output voltage and frequency, offering advantages like rapid response and controllability.