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
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Date
2010-08
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Publisher
The University of Dar es Salaam
Abstract
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 excellent performance of NCIs in Tanzania regardless of poor HC,
higher layer conductivity caused by high contamination, deterioration and damage.
Contamination caused failure of one insulator from Masaki substation with its surfaces
showing presence of oxidation and chalking products. In addition, High Voltage yard
insulators showed varying degrees of material deterioration and layer conductivity with
varying degrees of HC. 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.
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Keywords
High voltage insulators, Silicone rubber insulators, Ceramic insulators