Computation of Transmission Line Transients Including Corona Effects

Surges propagating on an overhead power transmission line are attenuated and distorted by a number of factors. Corona is probably the most significant one of all these factors for surges with sufficiently high crest values and steepness of fronts. A good understanding of the effect of corona is thus important in overvoltage protection and insulation coordination. The effect of corona on wave propagation has been under investigation with a long history. However, a satisfactory approach to include it quantitatively in the calculations of transmission line transients is still not available due to the intricacy of the mutual effect of corona and surges. Empirical formulas are still being used widely in the calculations for insulation designs and other purposes. Corona effect on travelling waves is attributed to the power loss and change in capacitance during corona. Early studies considered only one of these two aspects. Recent efforts have been made to combine both of them. This is achieved in this paper by simulating a non-linear capacitor having the same charge-voltage characteristics as the line in corona. From the point of view of the algorithms for the computation of transmission line transients, recent progress has been made in two directions. The first one is to solve numerically either the telegraphers' equations or the wave equation that describes the wave propagation on transmission lines. The finite different method is commonly used in this methodology. Convergence, stability, and efficiency are important here.