Probability distribution laws for switching overvoltages on mixed high voltage transmission lines

Inhalt:
Climate change has brought up the need of fundamental changes in the energy landscape. The transformation towards “all electric society” requires many changes and huge investments in transmission infrastructure. In opposition to this trend, the construction of new overhead transmission lines faces in many countries low acceptance levels from the public and leads to increased need for installation of high voltage underground cables and/or mixed lines with series connection of overhead line sections and insulated cables. For both transmission elements, the selection of an appropriate insulation level, based on the statistical methods of is high importance. Making an optimal choice for required transmission line reliability with a minimum of investment cost for the equipment insulation is required. At high voltages, the switching overvoltages risk of failure estimation is one important factor for the line insulation design. The random character of overvoltages magnitude, shape and of the breakdown voltage represents the main difficulty in risk of failure calculations. Therefore, is very important to have for both variables an accurate estimation of their probability distribution laws, especially for the case of mixed transmission lines. The paper presents results of a study on probability distribution laws for switching overvoltages on mixed high voltage transmission lines. Three distribution functions have been considered in the evaluation: normal, logarithmic normal and Weibull. Two tests, Kolmogorov-Smirnov and chi-square have been applied in order to estimate the agreement between the chosen distribution functions and the empirical one, determined by network simulations. The results underline the importance of the analysis on a case-by-case basis.