05-09-2014, 02:45 PM
power system stability improvemen
[attachment=67678]
INTRODUCTION
In the present scenario, most of the power systems in the developing countries with large interconnected networks share the generation reserves to increase the reliability of the power system. However, the increasing complexities of large interconnected networks had fluctuations in reliability of power supply, which resulted in system instability, difficult to control the power flow and security problems that resulted large number blackouts in different parts of the world. The reasons behind the above fault sequences may be due to the systematical errors in planning and operation, weak interconnection of the power system, lack of maintenance or due to overload of the network.
In order to overcome these consequences and to provide the desired power flow along with system stability and reliability, installations of new transmission lines are required. However, installation of new transmission lines with the large interconnected power system are limited to some of the factors like economic cost, environment related issues. These complexities in installing new transmission lines in a power system challenges the power engineers to research on the ways to increase the power flow with the existing transmission line without reduction in system stability and security.
In this research process, in the late 1980’s the Electric Power Research Institute (EPRI) introduced a concept of technology to improve the power flow, improve the system stability and reliability with the existing power systems. This technology of power electronic devices is termed as Flexible Alternating Current Transmission Systems (FACTS) technology. The potential of this technology is based on the possibility of controlling the route of the power flow and the ability of connecting networks that are not adequately interconnected, giving the possibility of trading energy between distant agents. Flexible Alternating Current Transmission System (FACTS) is a static equipment used for the AC transmission of electrical energy. It is meant to enhance controllability and increase power transfer capability. It is generally a power electronics based device. The FACTS devices can be divided in three groups, dependent on their switching technology: mechanically switched (such as phase shifting transformers), thyristor switched or fast switched, using IGBTs. While some types of FACTS, such as the phase shifting transformer (PST) and the static VAR compensator (SVC) are already well known and used in power systems, new developments in power electronics and control have extended the application range of FACTS. Furthermore, intermittent renewable energy sources and increasing international power flows provide new applications for FACTS. The additional flexibility and controllability of FACTS allow to mitigate the problems associated with the unreliable of supply issues of renewable. SVCs and STATCOM devices are well suited to provide ancillary services (such as voltage control) to the grid and fault rid through capabilities which standard wind farms cannot provide Furthermore, FACTS reduce oscillations in the grid, which is especially interesting when dealing with the stochastic behaviour of renewable.
Power System Constraints
The overall control task in an electric power system is to maintain the balance the electric power produced by the generators and the power consumed by the loads, including the network losses, at all time instants. If this balance is not kept, this will lead to frequency deviations that if too large will have serious impacts on the system operation. As, the transmission system is the high-voltage part of the electric power infrastructure responsible for the bulk transfer of electricity from power plants to substations located near population centres, they are being pushed closer to their stability and thermal limits while the focus is on the quality of power delivered is greater than ever. The limitations of the transmission system can take many forms and may involve power transfer between areas or within a single area or region and may include one or more of the following characteristics:
Controllability of Power Systems
To illustrate that the power system only has certain variables that can be impacted by control, we have considered here the power-angle curve, shown in Figure 2. Although this is a steady-state curve and the implementation of FACTS is primarily for dynamic issues, this illustration demonstrates the point that there are primarily three main variables that can be directly controlled in the power system to impact its performance
FACTS
A Flexible Alternating Current Transmission System (FACTS) is a system composed of static equipment used for the AC transmission of electrical energy. It is meant to enhance controllability and increase power transfer capability of the network. It is generally a power electronics-based system.
Given the nature of power electronics equipment, FACTS solutions will be particularly justifiable in applications requiring one or more of the following qualities:
• Rapid dynamic response
• Ability for frequent variations in output
• Smoothly adjustable output.
FACTS are a family of devices which can be inserted into power grids in series, in shunt, and in some cases, both in shunt and series.
CONCLUSION
Today, FACTS devices are individually controlled. But according to a new EPRI report, inventive strategies incorporating system-wide control logic could further increase power transfer capability, stability and reliability of transmission systems. Controllers would be able to maximize available transfer capacity which maintaining dynamic stability and security, which could help accommodate even more electricity transactions .The essential features of FACTS controllers and their potential to improve system stability is the prime concern for effective & economic operation of the power system. The coordination problem among different control schemes was also considered. Performance comparison of different FACTS controllers has been reviewed. The likely future direction of FACTS technology, was discussed. In addition, utility experience and major real-world installations and semiconductor technology development have been summarized. A brief review of FACTS applications to optimal power flow and deregulated electricity market has been presented.
[attachment=67678]
INTRODUCTION
In the present scenario, most of the power systems in the developing countries with large interconnected networks share the generation reserves to increase the reliability of the power system. However, the increasing complexities of large interconnected networks had fluctuations in reliability of power supply, which resulted in system instability, difficult to control the power flow and security problems that resulted large number blackouts in different parts of the world. The reasons behind the above fault sequences may be due to the systematical errors in planning and operation, weak interconnection of the power system, lack of maintenance or due to overload of the network.
In order to overcome these consequences and to provide the desired power flow along with system stability and reliability, installations of new transmission lines are required. However, installation of new transmission lines with the large interconnected power system are limited to some of the factors like economic cost, environment related issues. These complexities in installing new transmission lines in a power system challenges the power engineers to research on the ways to increase the power flow with the existing transmission line without reduction in system stability and security.
In this research process, in the late 1980’s the Electric Power Research Institute (EPRI) introduced a concept of technology to improve the power flow, improve the system stability and reliability with the existing power systems. This technology of power electronic devices is termed as Flexible Alternating Current Transmission Systems (FACTS) technology. The potential of this technology is based on the possibility of controlling the route of the power flow and the ability of connecting networks that are not adequately interconnected, giving the possibility of trading energy between distant agents. Flexible Alternating Current Transmission System (FACTS) is a static equipment used for the AC transmission of electrical energy. It is meant to enhance controllability and increase power transfer capability. It is generally a power electronics based device. The FACTS devices can be divided in three groups, dependent on their switching technology: mechanically switched (such as phase shifting transformers), thyristor switched or fast switched, using IGBTs. While some types of FACTS, such as the phase shifting transformer (PST) and the static VAR compensator (SVC) are already well known and used in power systems, new developments in power electronics and control have extended the application range of FACTS. Furthermore, intermittent renewable energy sources and increasing international power flows provide new applications for FACTS. The additional flexibility and controllability of FACTS allow to mitigate the problems associated with the unreliable of supply issues of renewable. SVCs and STATCOM devices are well suited to provide ancillary services (such as voltage control) to the grid and fault rid through capabilities which standard wind farms cannot provide Furthermore, FACTS reduce oscillations in the grid, which is especially interesting when dealing with the stochastic behaviour of renewable.
Power System Constraints
The overall control task in an electric power system is to maintain the balance the electric power produced by the generators and the power consumed by the loads, including the network losses, at all time instants. If this balance is not kept, this will lead to frequency deviations that if too large will have serious impacts on the system operation. As, the transmission system is the high-voltage part of the electric power infrastructure responsible for the bulk transfer of electricity from power plants to substations located near population centres, they are being pushed closer to their stability and thermal limits while the focus is on the quality of power delivered is greater than ever. The limitations of the transmission system can take many forms and may involve power transfer between areas or within a single area or region and may include one or more of the following characteristics:
Controllability of Power Systems
To illustrate that the power system only has certain variables that can be impacted by control, we have considered here the power-angle curve, shown in Figure 2. Although this is a steady-state curve and the implementation of FACTS is primarily for dynamic issues, this illustration demonstrates the point that there are primarily three main variables that can be directly controlled in the power system to impact its performance
FACTS
A Flexible Alternating Current Transmission System (FACTS) is a system composed of static equipment used for the AC transmission of electrical energy. It is meant to enhance controllability and increase power transfer capability of the network. It is generally a power electronics-based system.
Given the nature of power electronics equipment, FACTS solutions will be particularly justifiable in applications requiring one or more of the following qualities:
• Rapid dynamic response
• Ability for frequent variations in output
• Smoothly adjustable output.
FACTS are a family of devices which can be inserted into power grids in series, in shunt, and in some cases, both in shunt and series.
CONCLUSION
Today, FACTS devices are individually controlled. But according to a new EPRI report, inventive strategies incorporating system-wide control logic could further increase power transfer capability, stability and reliability of transmission systems. Controllers would be able to maximize available transfer capacity which maintaining dynamic stability and security, which could help accommodate even more electricity transactions .The essential features of FACTS controllers and their potential to improve system stability is the prime concern for effective & economic operation of the power system. The coordination problem among different control schemes was also considered. Performance comparison of different FACTS controllers has been reviewed. The likely future direction of FACTS technology, was discussed. In addition, utility experience and major real-world installations and semiconductor technology development have been summarized. A brief review of FACTS applications to optimal power flow and deregulated electricity market has been presented.