Transmission lines located in the desert are subjected to desert climate, one of whose features is
sandstorms. With long accumulation of sand and with the advent of moisture from rain, ambient
humidity and dew, a conductive layer forms and the subsequent leakage current may lead to
surface discharge, which may shorten the insulator life or lead to flashover thus interrupting the
power supply. Strategically erected power lines in the Egyptian Sinai desert are typically subject
to such a risk, where sandstorms are known to be common especially in the spring. In view of
the very high cost of insulator cleaning operation, composite (silicon rubber) insulators are
nominated to replace ceramic insulators on transmission lines in Sinai. This paper examines
the flow of leakage current on sand-polluted composite insulators, which in turn enables a risk
assessment of insulator failure. The study uses realistic data compiled and reported in an earlier
research project about Sinai, which primarily included grain sizes of polluting sand as well as
their salinity content. The paper also uses as a case study an ABB-designed composite insulator.
A three-dimensional finite element technique is used to simulate the insulator and seek the
potential and electric field distribution as well as the resulting leakage current flow on its polluted
surface. A novel method is used to derive the probabilistic features of the insulator’s leakage
current, which in turn enables a risk assessment of insulator failure. This study is expected
to help in critically assessing – and thus justifying – the use of this type of insulators in Sinai and
similar critical areas.