Abstract :
The paper outlines an investigation which was initiated to obtain an understanding of the mechanism by which overvoltages, of sufficient magnitude to cause flashover, are produced on a line section which forms part of a 132kV system. The line is terminated at one end with a series-connected inductor; the overvoltage occurs when the line is initially energised by an air circuit breaker at the other end. Basic data regarding the high-frequency performance of current-limiting inductors of different manufacturers have been obtained by measurement on site. This information is used, in conjunction with an estimate of the earth-capacitance distribution along the inductor winding, to obtain a simple equivalent circuit which is representative in the kilocycle-per-second range of frequencies. Owing to lack of access, the line parameters have been estimated from the known characteristics of other lines. The usual approach to a theoretical solution of the problem, by the use of transforms and lattice diagrams, is shown by simple examples to fall short of the requirements when reactive terminations are involved. A new approach, using a Fourier series, is shown to provide the required solutions. This form of analysis is explained in terms of the frequency response of the system, and the results are verified by crosschecking using various line-inductor combinations on a laboratory model. These model tests have also helped to provide an understanding of the action of various independent variables met with on the system, e.g. the effect of changes of source impedance. The results of the analysis and tests indicate that the overvoltage produced may be of the order of five times the peak phase-to-earth voltage of the system. To assist with estimating the probable overvoltages in similar circumstances, a curve has been obtained from a computer, showing the overvoltage against line length for a particular inductor. It is indicated that this method of solution can be used to determine sy- stem performance where more complicated terminations are used.
