Research On Fault Location Technology For Extra-high Voltage Mixed Overhead Lines And Cables

Fault location for mixed overhead lines and cables gets more attention with the widely use of mixed lines. Fast faulted section identification and precise fault location for mixed lines contribute to a right action of re-closure and a quick recovery of power supply. Currently most research at home and abroad is in relation to uniform overhead transmission lines. Whether or not these fault location algorithms for overhead lines can be used for mixed lines is another question to be considered. Therefore, it is necessary to summarize the advantages and disadvantages of the current research, and find a new algorithm and method for mixed line fault location.This paper firstly summarizes the current research status for mixed line fault location. According to different fault location principles, the algorithm for mixed overhead lines and cables can be classified into algorithm based on power frequency, algorithm based on travelling wave, combined algorithm based on power frequency and travelling wave, algorithm based on artificial intelligence. Algorithm based on power frequency is chosen in this paper after comparison.A new fault location algorithm for extra-high voltage mixed lines based on phase characteristics of the faulted section identification functions is proposed. Overhead-cable-overhead lines is taken as an example to illustrate the principle. Faulted section identification functions for overhead-cable connections described by hyperbolic tangent are developed separately when faults occur on the first overhead line, on the middle cable and on the last overhead line. When fault occurs on different sections, the faulted section identification functions appear obviously different phase characteristics according to the phase characteristics of hyperbolic tangent function. Thus the faulted section can be identified. The fault location can be therefore accurately determined with the voltage and current positive sequence fault components on both ends of the faulted section. Simulations and calculations with PSCAD and MATALB show that the fault location algorithm is of high reliability and accuracy and is not influenced by load current, fault type, fault resistance, initial angles, lines parameters and asynchronous data. The algorithm can be used for mixed lines with more sections.A universal method is proposed in order to apply algorithms developed for uniform overhead lines into mixed lines. This method take each section of the mixed lines as a separate uniform line. The algorithm for uniform overhead lines is used for each section to calculate a ratio which equals the calculated fault location divides by the length of the section. According to the range and phase characteristics of each ratio for each section, the faulted section can be identified and the exact fault location can be calculated. Simulations and calculations with PSCAD and MATALB show that the algorithm is robust and is of high reliability and accuracy.A fault location algorithm for uniform overhead lines based on the phase characteristics of the fault location function is introduced. The algorithm then is used for mixed lines. The ratio for each section is calculated and according to the range and phase characteristics of each ratio for each section, the faulted section can be identified and the exact fault location can be calculated. Simulations and calculations with PSCAD and MATALB show that the universal method is effective.