Establishment Of The Mathematical Model In The Malfunction Calculation Of Power Transmission Circuit With 500Kv Extra-High Voltage And Long Distance

Based on the project of power transmission from Yangcheng Power Plant in Shanxi Province to Jiangsu Province and using distributed parameters, this paper derive the mathematical models of long Extra High Voltage (EHV) transmission lines with series capacitor compensation. What have been summed up in this paper are the traditional protection principles of EHV transmission lines and factors influencing the accuracy of protection, and some solution to these problems have also been given. The focus of this paper is the influence of series capacitor and its protection on high frequency transient component of faults current. Matlab, a simulation tool for power system, has been adopted to simulate long EHV transimission line with series capacitor compensation. As it possesses the properties of multi-scale analysis and of time-frequency localization, wavelet transform is particularly well adapted to the processing of sharply changing signals and to extracting of characteristic of those signals. A large amount of study utilizing wavelet multi-scale edge detection method has been made of singularity degree of tiansient current signal in EHV transimission line at sudden change point. The author also proves that series capacitor compensation does not affect propagation constant of transimission line. Through the snalysis using Wavelet Toolboxin Matlab, the author concludes that the non-unit transient protection criterion of using the energy descent rates of differentfrequencies dring a certain period, and of detecting lipschiz degree of different frequencies during a certain period, and of detecing lipschiz degree at singularity poing, to distinguish internal and exetemal faults, are inapplicable to the EHV transmission line with series capacitor compensation. Thus the author provides a new criterion suitable for the transient based protection of EHV transmission lines with series capacitor compensation. The results of simulation denote that the new methods in this paper are officient and reliable. Finally, the author presents some suggestions on line protection design.