Principles of the Choice of Support Insulators under the Conditions of Their Pollution and Moistening

To determine whether the electrical strength of polluted insulators complies with the requirements of regulatory documents in international and domestic practice, tests are carried out using two main methods: solid layer and salt fog. The first method applies to insulators designed to operate in continental regions, and the second method applies to insulators supplied to seashore regions. It is shown that when choosing insulators tested by the solid layer method, excessively increased values of the ratio of the creepage distance to the insulating height of the insulator L/H are allowed, and design solutions are obtained that a priori lead to a nonuniform distribution of voltage along insulating columns consisting of two or more elements. All these features negatively affect the insulation electrical strength and often lead to negative test results. The insulator selection principles are proposed that are based on the following main criterion: ensuring conditions for the effective use of the creepage distance by the arc discharge. For insulators designed to operate in continental regions, this criterion applies in the area of L/H ≤ (L/H)opt. It is shown that the recommendations of international regulatory documents on the upper limits of the L/H ratio are acceptable for insulators operating in seashore regions and are not acceptable for insulators operated far away from the sea. It has been found that, due to the nonuniform distribution of leakage current density, even with a uniform distribution of voltage across the column elements with different geometric parameters, it is not possible to ensure the maximum possible electrical strength of the structure.