A comparison between the chemical effects of degradation and the physical and electrical performance of EPDM rubber

A major drawback to the use of composite insulators is that the polymeric shed material ages and the limitations this imposes on the lifetime of insulators is at this stage unknown. The authors and co-workers have used advanced chemical analysis methods such as emission FTIR and XPS to study the ageing of field-aged insulators and results from this work have indicated that ageing of EPDM materials appears to be due to the combined effects of UV and surface discharging. In this paper the results of fundamental laboratory studies made to examine the factors affecting the rate of degradation of EPDM are presented. The ageing of thin film samples of uncrosslinked EPDM polymer was studied, as well as the ageing of ATH (Aluminium tri hydroxide) filled materials. Degradation was induced by high temperature operation and UVA. The chemical composition of the samples during ageing was measured using Fourier transform infrared absorbance spectroscopy and differential scanning calorimetry. Surface properties were monitored by contact angle measurement. The kinetics for the degradation of the model insulator materials are presented. Results from these tests are also compared with results of physical measurements of surface hydrophobicity and a correlation is made between this and the chemical tests. The most important factors contributing to the ageing of the EPDM samples are identified and the relative usefulness of the chemical and physical tests in providing information about insulator condition are discussed.