Ultrasonic detection of absorbed water in solid insulation

Polymeric high voltage insulation systems are often prone to water absorption when used in outdoor applications. If the insulation is not shielded from the elements, water can be slowly absorbed over a number of years. This process is accelerated if the temperature is raised or if the absorption takes place under the influence of an electric field. The presence of water invariably affects the integrity of the insulation and can promote a number of different breakdown scenarios. This paper describes a method for determining the water content of a polymer using commercially available ultrasonic non-destructive testing equipment. Two types of insulation commonly prone to degradation by water have been tested