9291_c010 - 10 Voltage Stability 10.1 Basic Concepts. 10-1...

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10 Voltage Stability Yakout Mansour California ISO Claud io Ca n ˜ izare s University of Waterloo 10.1 Basic Concepts. ................................................................ 10 -1 Generator-Load Example . Load Modeling . Effect of Load Dynamics on Voltage Stability 10.2 Analytical Framework . .................................................... 10 -8 Power Flow Analysis . Continuation Methods . Optimization or Direct Methods . Timescale Decomposition 10.3 Mitigation of Voltage Stability Problems. ................... 10 -11 Voltage stability refers to ‘‘the ability of a power system to maintain steady voltages at all buses in the system after being subjected to a disturbance from a given initial operating condition’’ (IEEE-CIGRE, 2004). If voltage stability exists, the voltage and power of the system will be controllable at all times. In general, the inability of the system to supply the required demand leads to voltage instability (voltage collapse). The nature of voltage instability phenomena can be either fast (short-term, with voltage collapse in the order of fractions of a second to a few seconds) or slow (long-term, with voltage collapse in minutes to hours) (IEEE-CIGRE, 2004). Short-term voltage stability problems are usually associated with the rapid response of voltage controllers (e.g., generators’ automatic voltage regulator [AVR]) and power electronic converters, such as those encountered in flexible AC transmission system or FACTS control- lers and high voltage DC (HVDC) links. In the case of voltage regulators, voltage instability is usually related to inappropriate tuning of the system controllers. Voltage stability in converters, on the other hand, is associated with commutation issues in the electronic switches that make up the converters, particularly when these converters are connected to ‘‘weak’’ AC systems, i.e., systems with poor reactive power support. These fast voltage stability problems have been studied using a variety of analysis techniques and tools that properly model and simulate the dynamic response of the voltage controllers and converters under study, such as transient stability programs and electromagnetic transient simu- lators. This chapter does not discuss these particular issues, concentrating rather on a detailed presen- tation of long-term voltage instability phenomena in power systems. 10.1 Basic Concepts Voltage instability of radial distribution systems has been well recognized and understood for decades (Venikov, 1970, 1980) and was often referred to as load instability. Large interconnected power networks did not face the phenomenon until late 1970s and early 1980s. Most of the early developments of the major high voltage (HV) and extra HV (EHV) networks and interties faced the classical machine angle stability problem. Innovations in both analytical techniques and stabilizingmeasures madeit possibletomaximizethepower transfercapabilitiesofthe transmissionsystems.
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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_c010 - 10 Voltage Stability 10.1 Basic Concepts. 10-1...

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