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System Integrity Protection Scheme Based on PMU Technology

The Power Transmission System (PTS) has to meet strict demands for greater reliability, with fewer investments made into the main infrastructure. By implementing new digital and adaptive solutions for protection and control of the entire PTS, a new generation of the transmission system will be created, which is widely known as Intelligent Power Transmission System or Smart Transmission Grid. Liberalization of electricity market, generation from distributed renewable energy sources (RES) and continuous growth in energy consumption set economic profit ahead of technological requirements, as a determining factor in strategic decisions of power system development. Consequences are reaching as far as fewer investments into construction of new facilities, especially of the transmission system, which again results in questionable protection and control, with lowered protection margins. This challenge requires new technological solutions that will be able to meet real time monitoring, protection and control demands. The aim of many experts all over the world is research and development of an Intelligent System for protection and control of the PTS, as well as its deployment in a section of the PTS. The Intelligent System requires the creation of a System Integrity Protection Scheme (SIPS) in case of failure. Also, adequate circuit architecture, necessary for the implementation of the developed system scheme, has to be created and deployed. Wide Area Monitoring, Protection and Control (WAMPAC) is a concept that uses Synchronized Measurement Technology (SMT) to counteract the propagation of large disturbances. Monitoring of wide-area (WAMS) is the main function currently implemented in power systems, but with the development of protection and control schemes, WAMPAC is expected to improve security and reliability of power system operation, as well as disturbances mitigation and blackout prevention. Although the idea of synchronized measurement is not new, its implementation is enabled with the use of time stamp from GPS. Also, implementation of the wide area schemes becomes possible due to the lower costs of technologies such as PMUs, PDCs and modern communication infrastructure. Energy consumption increase and the modern trends in the electric power system operation force the grid to operate closely to its stability limits with small power margins. Rapid development of electric power market, where often technical aspect is not emphasizes enough, but only economical one, treating electric power as any other merchandise, puts additional effort on the infrastructure which is not always upgraded or maintained as it should be. As a result we can witness huge electric power blackouts, some of them in the last decade. Power blackouts are low probability but extremely costly conditions, which frequency is increasing over years, due to the grid complexity and trends which comprise distributed renewable energy, two way power flow, deregulation, liberalization, etc.. Usually the triggering event is a contingency or a combination of few events. Such wide area disturbances cannot be treated or even “seen” by using local measurement and systems. For wide-area monitoring, protection and control, and in the end maintaining power system integrity, information about the system state must be available in the real-time. Cascading blackouts can affect national, regional or continental power systems. Therefore, efficient tool for detection and prevention of disturbances which can cause wide-area blackouts must be developed and deployed. As the blackout risk can be represented as the multiplication of the blackout probability and the cost it produces, effective solutions should be found in order to decrease both factors. WAMS offers multiple benefits such as stability, reliability and safety of supply. Also, it has economical effect if the system is operated closer to the grid’s stability and capacity limits, which leads to the increased energy transfer. General trend is to operate power grid close to its stability limits in order to increase power transfer capacity, consequently decreasing safety margins and increasing disturbances and blackout risk. Realistic solution can be found in real-time wide area monitoring, which is based on synchronized phasor measurements (amplitude and phasor angle) of voltages and currents and their frequencies. WAMS measurement data enable real-time monitoring and it can be used as an early warning system – system which uses a fast diagnostic and gives the operator enough time to make required steps for system stability in order to limit disturbance’s range and impact and to prevent power system blackout. Analyses of the major system blackouts in the last few decades show that the operator mistake was the initial event in about 10% of all the cases. Taking into the consideration blackout cost and consequences, even minor reduction in the blackout risk would result in a vast savings. WAMPAC has indirect impact on the system blackout caused by the operator mistake. The operators have the main role in the safe system operation and it can be assumed that they are highly qualified, educated and monitored in their work and that accidental mistakes happen rarely. Main goal of the quality monitoring system is to supply the operator with the real-time data about the power grid and its state in order to ensure him enough time for quality decisions and fast reactions. Intention is to use WAMPAC and implemented concepts of SIPS (System Integrity Protection Schemes) to discover and treat real- time disturbances in wide-area in order to prevent system blackout and maintain integrity of the whole power system, not just locally or focused on particular element of the grid. Direct WAMS impact on the system reliability and blackout risk cannot be easily or explicitly expressed, but increased accuracy, additional functions and applications, chronological event registration with time stamps via GPS, as well as future developments in the protection and control field, would significantly improve power grid operation and play main role in decreasing blackout risk.

PMU Technology ; SIPS ; Islanding ; WAMPAC ; Power System Control

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