9291_c012 - 12 Power System Stability Controls 12.1 12.2...

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12 Power System Stability Controls Carson W. Taylor Carson Taylor Seminars 12.1 Review of Power System Synchronous Stability Basics . ............................................................................... 12 -2 12.2 Concepts of Power System Stability Controls . ............. 12 -5 Feedback Controls . Feedforward Controls . Synchronizing and Damping Torques . Effectiveness and Robustness . Actuators . Reliability Criteria 12.3 Types of Power System Stability Controls and Possibilities for Advanced Control . ............................... 12 -7 Excitation Control . Prime Mover Control Including Fast Valving . Generator Tripping . Fast Fault Clearing, High-Speed Reclosing, and Single-Pole Switching . Dynamic Braking . Load Tripping and Modulation . Reactive Power Compensation Switching or Modulation . Current Injection by Voltage Sourced Inverters . Fast Voltage Phase Angle Control . HVDC Link Supplementary Controls . Adjustable Speed (Doubly Fed) Synchronous Machines . Controlled Separation and Underfrequency Load Shedding 12.4 Dynamic Security Assessment. ..................................... 12 -14 12.5 ‘‘Intelligent’’ Controls. ................................................... 12 -14 12.6 Wide-Area Stability Controls . ...................................... 12 -15 12.7 Effect of Industry Restructuring on Stability Controls. .......................................................... 12 -16 12.8 Experience from Recent Power Failures. ..................... 12 -16 12.9 Summary. ....................................................................... 12 -16 Power system synchronous or angle instability phenomenon limits power transfer, especially where transmission distances are long. This is well recognized and many methods have been developed to improve stability and increase allowable power transfers. The synchronous stability problem has been fairly well solved by fast fault clearing, thyristor exciters, power system stabilizers (PSSs), and a variety of other stability controls such as generator tripping. Fault clearing of severe short circuits can be less than three cycles (50 ms for 60 Hz frequency) and the effect of the faulted line outage on generator acceleration and stability may be greater than that of the fault itself. The severe multiphase short circuits are infrequent on extra high voltage (EHV) transmission networks. Nevertheless, more intensive use of available generation and transmission, more onerous load characteristics, greater variation in power schedules, and other negative aspects of industry restructuring pose new concerns. Recent large-scale cascading power failures have heightened the concerns. In this chapter we describe the state-of-the-art of power system angle stability controls. Controls for voltage stability are described in another chapter and in other literature [1–5]. ß 2006 by Taylor & Francis Group, LLC.
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We emphasize controls employing relatively new technologies that have actually been implemented by electric power companies, or that are seriously being considered for implementation. The technologies include applied control theory, power electronics, microprocessors, signal processing, transducers, and communications. Power system stability controls must be effective and robust. Effective in an engineering sense means ‘‘cost-effective.’’ Control robustness is the capability to operate appropriately for a wide range of power system operating and disturbance conditions.
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9291_c012 - 12 Power System Stability Controls 12.1 12.2...

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