Studies On Voltage Control Area Of Electrical Power System

Following the development of electrical power industry, voltage stability andcollapse problems appear gradually and have given cause for cascading in somepower systems. So, they attract more and more attention of power engineers. With thedesire of preventing faults of voltage collapse away from power system and keeping itstable in voltage, operators want most to know if the power system was stable involtage and how far it is apart from the critical point of voltage stability. Based on theGlobal Position System (GPS) and the Phasor Measurement Unit (PMU), it ispossible to observe power system's dynamic behaviour and so a powerful tool toanswer the two questions above is provided. To apply this powerful tool in the actualsystems, what we should do first is to answer two another questions that how to locatePMUs in power systems and how to use the information they provide. Answers to thetwo questions form the main part of this thesis.Firstly, to select representative buses for PMU locating, the whole system shouldbe divided into different areas in advance according to the character of the areareactive power which should be balanced locally. This thesis has compared severaldifferent methods of system dividing and chooses Voltage Control Area (VCA) as thebest one. And then it analyses this method in view of its physical meanings and pointsout its bug in the step of small elements eliminating matrix selection. Based on theresults above, a new idea of using the sum of P-V and Q-V parts of the NewtonRaphson load flow Jacobian matrix to get VCAs is adopted for the first time. Besides,the modifying process of traditional VCA partition methods is completed necessarilyin the thesis by using the most terrible system topology changes to modify VCAs. Theefficiency and veracity of VCAs got by the improved method are testified in the10-generator, 39-bus New England Test System.Secondly, the thesis discusses the relation of power system transient voltagestability and the dynamic characters of loads, and then points out the difficulty ofcreating a transient voltage stability index according to the loads'dynamic characters.In order to obtain a simple index, the thesis selects several representative buses, ofwhich each one was most sensitive to the system disturbance in its own VCA,according to the voltage variation of all buses after system topology changes in eachVCA based on the VCAs obtained by the improved method. And then theserepresentative buses'real time status messages are used to create a transient voltagestability index.Finally, we illuminate that even when the system's operating mode was changed,the VCAs obtained by the improved method are still appropriate in voltage stabilityanalysis of the system.