Failure analysis of extra-high voltage (EHV) hot sticks

Abstract

After three field flashover failures of EHV hot sticks, two in Canada at 500 kV and one in the USA at 345 kV, a study of the present day maintenance and testing methods was needed. Experimentation does show that rubbing of the fiberglass reinforced plastic (FRF) over aluminum, aged conductors, and galvanizing will deposit micron size conductive particles onto the insulating medium. The need for a new method of testing was suggested because these field failures implied that the testing methods being used might not have been sufficient in sensitivity to find the problems before they caused a field failure. The low voltage testing methods used for hot stick testing will be compared to aerial lift testing per ANSI-A92.2. In so doing, it may become evident that the evolution of hot stick testing needs a quantum leap in sensitivity to prevent future field failures. The reality of moisture having the capability to penetrate through FRF material will be demonstrated several ways. Moisture spots or an accumulation of metallic contamination that cannot be removed by normal cleaning techniques may determine the end of life of EHV hot sticks. Photographs of the conductive contamination will be provided in the technical paper. The metallic material has been found to be difficult to remove in the cleaning process since it is difficult to see with a 100 X microscope. To insure the flashover resistance of this very important insulation, it is recommended to go at least 700 kV for at least five seconds to make sure the flashover resistance is there. In addition work methods will be addressed, stressing the importance of proper care when installing, using, storing, and maintaining these tools to prevent surface contamination that can lead to reduction of the insulating integrity.