Non-ceramic insulators in coastal tropical climates: the case study of Tanzania field performance of polymeric insulators and dielectric characteristics of silicone rubber and epoxy resin formulations

Since use of non-ceramic insulators (NCIs) began worldwide in 1970s, researchers have been busy perfecting these products, monitoring them in service and analysing their failure modes. In Tanzania, there is need to monitor and evaluate NCIs for use in its tropical climates. This tropical climate is characterised by heavy rains, high insolation resulting to high temperatures and high humidity. One aim is to investigate and evaluate aging and performance of NCIs in these climates regarding their hydrophobicity (HC), layer conductivity, quantifying oxidation and chalking indices. Another aim is investigation in order to characterise the dielectric properties of polymeric formulations. Achieving those objectives necessitated adopting methods such as field visits, Swedish Transmission Research Institute (STRI) guide for HC measurements, guide for visual observations of damage and deterioration (STRI, 2005) and Fourier Transform Infrared Spectroscopy (FTIR) spectra. In addition, characterising the polymeric formulations used surface and volume resistivity methods and dielectric frequency spectroscopy. Fit of the resistivity data to curves used robust regression methods, which are resistant to outliers. Results indicated that, in Tanzania regardless of poor HC, higher layer conductivity caused by high contamination, deterioration and damage; there is only one NCI flashover at Masaki Substation for 10 years of service, no failures for over 36 years of NCIs service at Ruvu Chini, and no failure for over 10 years at all other (NCIs) feeders investigated. The failed Masaki substation NCI showed surfaces containing oxidation and chalking products. In addition, High Voltage yard insulators showed varying degrees of material deterioration and layer conductivity with varying degrees of HC after 2 years hanging outdoors un-energized. Dielectric characterisation of polymeric formulations showed higher surface and volume resistivities. Furthermore, there were higher dielectric losses in silicone rubber (SIR) than in epoxy resin. SIR displayed both low and higher frequency relaxations whereas epoxy resin displayed higher frequency relaxations. There was low and higher frequency relaxation exacerbated by electrode polarisation in series combined SIR and epoxy resin. The dielectric losses contained dc conductivity, hopping conductivity and electrode polarisations. With these findings, the Tanzania utility is urged to speed up upgrading insulation for distribution and transmission lines. In addition, it could set up a R&D department to deal with NCIs.