Design criteria for composite insulators

Composite insulators for overhead power lines are no longer new or untried products. With a service history of more than 15 years, it is possible to say that a well-designed composite insulator is reliable in the long term and may often prove the more economic solution. Here, the authors describe how, in selecting a composite insulator, it is important to consider a wide variety of design criteria, not simply the question of the covering material used. An insulator must be designed to fulfil all of its mechanical and electrical functions for the duration of its service life under all possible conditions. Injection moulding of the rod covering and weathersheds as one unit is shown to provide a reliable process and facilitates verification of interfaces, so eliminating the risk of puncture between weathersheds and the possibility of moisture ingress