Surface charging characteristics of fiberglass reinforced plastic (FRP) hot sticks under HVDC operating conditions

Currently, more and more industrial interest is given to surface charging of polymeric materials and their flashover performance. This paper focuses on studying the surface charge characteristics found on the surface of fiberglass reinforced plastic (FRP) hot-sticks during live-line maintenance work. In this work, three sources for depositing space charges to the surface of the FRP sample are used. Corona discharge are generated by a ring of needles that is energized by both polarities of a DC voltage. Corona discharge along the sample surface are also generated by pre-stressing using positive or negative DC voltages. Another source of charge deposition is by friction when the surface of the hot-stick is wiped by a cotton cloth and/or silicone cloth. Wiping is an on-site routine done before live-line maintenance work. A cylindrical FRP sample, 130 mm long with a diameter of 38 mm, is used throughout the study. Surface potentials are measured by means of a vibrating Kelvin probe connected to an electrostatic voltmeter. The measured surface potential values are captured and stored in a computer using a data acquisition system. The probe response matrix is numerically calculated using the finite element method. The measured surface potential values are used to calculate the corresponding charge density distributions by using the probe response matrix method. It has been found that, for both positive and negative charging voltages, the measured surface potentials have bell shapes and their magnitudes increase proportionally with the charging voltage. Charging by pre-stressing results in depositing hetero-charges along the entire sample surface with a smaller amount of homo-charges close to the electrodes. Wiping the FRP samples produces large amounts of positive charges on its surface as compared to the other two charging methods.