9291_c004 - 4 System Protection Miroslav Begovic Georgia...

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Unformatted text preview: 4 System Protection Miroslav Begovic Georgia Institute of Technology 4.1 Introduction......................................................................... 4-1 4.2 Disturbances: Causes and Remedial Measures ................. 4-1 4.3 Transient Stability and Out-of-Step Protection................ 4-2 4.4 Overload and Underfrequency Load Shedding ................ 4-3 4.5 Voltage Stability and Undervoltage Load Shedding......... 4-4 4.6 Special Protection Schemes ................................................ 4-6 4.7 Modern Perspective: Technology Infrastructure............... 4-7 Phasor Measurement Technology . Communication Technology 4.8 Future Improvements in Control and Protection............ 4-9 4.1 Introduction While most of the protective system designs are made around individual components, system-wide disturbances in power systems are becoming a frequent and challenging problem for the electric utilities. The occurrence of major disturbances in power systems requires coordinated protection and control actions to stop the system degradation, restore the normal state, and minimize the impact of the disturbance. Local protection systems are often not capable of protecting the overall system, which may be affected by the disturbance. Among the phenomena, which create the power system, disturb- ances are various types of system instability, overloads, and power system cascading [1–5]. The power system planning has to account for tight operating margins, with less redundancy, because of new constraints placed by restructuring of the entire industry. The advanced measurement and communication technology in wide area monitoring and control are expected to provide new, faster, and better ways to detect and control an emergency [6]. 4.2 Disturbances: Causes and Remedial Measures [7] Phenomena that create power system disturbances are divided, among others, into the following categories: transient instabilities, voltage instabilities, overloads, power system cascading, etc. They are mitigated using a variety of protective relaying and emergency control measures. Out-of-step protection has the objective to eliminate the possibility of damage to generators as a result of an out-of-step condition. In case the power system separation is imminent, it should separate the system along the boundaries, which will form islands with balanced load and generation. Distance relays are often used to provide an out-of-step protection function, whereby they are called upon to provide blocking or tripping signals upon detecting an out-of-step condition. The most common predictive scheme to combat loss of synchronism is the equal-area criterion and its variations. This method assumes that the power system behaves like an equivalent two-machine model ß 2006 by Taylor & Francis Group, LLC. where one area oscillates against the rest of the system. Whenever the underlying assumption holds true, the method has potential for fast detection....
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9291_c004 - 4 System Protection Miroslav Begovic Georgia...

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