Electrical, physical and chemical measurements on electric field degraded polyethylene

The surface degradation of polyethylene insulators under high electrical stress can be investigated using several surface techniques in conjunction with discharge current measurements. Degradation occurred in air with relative humidities of 25 to 75 percent. The electrical discharge measurements include both pulse (partial discharge) and direct current (DC) values. Humidity influences the partial discharge and DC currents. At higher relative humidities partial discharge current increases and DC current decreases. The surface analysis techniques include surface resistivity, X-ray photoelectron spectroscopy (XPS) and atomic force microscopy (AFM) roughness measurements. Measurement of surface resistivity is dependent on relative humidity. Surface resistivity decreases with increasing relative humidity which may be a boundary condition for decreased discharge currents. The measurement techniques necessary to quantify such parameters are discussed. The utility of antioxidants for retardation of electrical degradation is also investigated. Antioxidant performance for thermal stabilization of thermoplastics is well established through tests such as oxidative induction time tests. Proposed chemical mechanisms for electric field induced degradation are similar to chemical mechanisms for thermally induced degradation. The performance of antioxidants as high electrical stress stabilizers is reported, as measured by XPS.