Natural insulator contamination test results on various shed shapes in heavy industrial contamination areas

In Shanghai, China, industrial contamination is very severe and periodic insulator washing is performed not only in substations but also on transmission lines. In order to review the present insulator contamination design and maintenance practices, a series of periodical contamination measurements under de-energized conditions were made. Also insulators that had been energized at two sites for one year were removed, and withstand voltage tests were conducted in an artificial fog chamber. Unexpectedly high ESDD (Equivalent Salt Deposit Density) values >1 mg/cm² and NSDD (Nonsoluble Deposit Density) values over >5 mg/cm² were measured. Aerodynamic type insulators showed a smaller accumulation of contamination than deep-rib type insulators. However, no significant difference can be seen between aerodynamic type and deep-rib type insulators in the withstand voltage per unit insulator string length. CaSO_4/12H₂O (Bassanite) is identified as the most dominant soluble contaminant