9291_c021 - 21 Security Analysis 21.1 21.2 21.3 21.4...

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21 Security Analysis Nouredine Hadjsaid Institut National Polytechnique de Grenoble (INPG) 21.1 Definition. ........................................................................ 21 -2 21.2 Time Frames for Security-Related Decision . ................ 21 -2 21.3 Models. ............................................................................. 21 -3 21.4 Determinist vs. Probabilistic . ......................................... 21 -5 Security under Deregulation Appendix A . ................................................................................ 21 -5 Appendix B . ................................................................................ 21 -6 The power system as a single entity is considered the most complex system ever built. It consists of various equipment with different levels of sophistication, complex and nonlinear loads, various gener- ations with a wide variety of dynamic responses, a large-scale protection system, a wide-area commu- nication network, and numerous control devices and control centers. This equipment is connected with a large network (transformers, transmission lines) where a significant amount of energy transfer often occurs. This system, in addition to the assurance of good operation of its various equipment, is characterized by an important and simple rule: electricity should be delivered to where it is required in due time and with appropriate features such as frequency and voltage quality. Environmental constraints, the high cost of transmission investments and low = long capital recovery, and the willing of utilities to optimize their network for more cost effectiveness makes it very difficult to expand or oversize power systems. These constraints have pushed power systems to be operated close to their technical limits, thus reducing security margins. On the other hand, power systems are continuously subjected to random and various disturbances that may, under certain circumstances, lead to inappropriate or unacceptable operation and system conditions. These effects may include cascading outages, system separation, widespread outages, viola- tion of emergency limits of line current, bus voltages, system frequency, and loss of synchronism (Debs and Benson, 1975). Furthermore, despite advanced supervisory control and data acquisition systems that help the operator to control system equipment (circuit breakers, on-line tap changers, compensa- tion and control devices, etc.), changes can occur so fast that the operator may not have enough time to ensure system security. Hence, it is important for the operator not only to maintain the state of the system within acceptable and secure operating conditions but also to integrate preventive functions. These functions should allow him enough time to optimize his system (reduction of the probability of occurrence of abnormal or critical situations) and to ensure recovery of a safe and secure situation. Even though for small-scale systems the operator may eventually, on the basis of his experience, prevent the consequences of most common outages and determine the appropriate means to restore a secure state, this is almost impossible for large systems. It is therefore essential for operators to have at their disposal, efficient tools capable of handling a systematic security analysis. This can be achieved through the diagnosis of all contingencies that may have serious consequences. This is the concern of security analysis .
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This note was uploaded on 03/03/2010 for the course POWER 332 taught by Professor Dr during the Spring '10 term at Ain Shams University.

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9291_c021 - 21 Security Analysis 21.1 21.2 21.3 21.4...

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