ABSTRACT
This chapter presents the characteristics of air-porcelain insulations subjected to lightning and switching impulses. In addition, the lightning impulse strength of wood or fiberglass in series with air-porcelain insulation is discussed. To determine the switching impulse (SI) strength of a tower, a full-scale simulated tower is created in a high-voltage laboratory. The lightning impulse (LI) strength is usually specified only by the CFO. However, benefiting from the results from switching impulse strength investigations, it is quickly realized that the LI strength characteristic can also be modelled as a cumulative Gaussian distribution having a mean value equal to the CFO and a standard deviation. The CFO of the outside phase with V-string insulator strings should be expected to have a larger CFO than that of the center phase, since there exists only one tower side. A general approach to the estimation of the positive polarity CFO for alternate gap configurations was suggested by Paris and Cortina in 1968.
