Degradation analysis of metal oxide varistors under harmonic distortion conditions
Date
2016-10-11
Authors
Bokoro, Pitshou Ntambu
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Abstract
Modern electrical networks provide an opportunity for inevitable interaction between
metal oxide arresters and power system harmonics. Therefore, these arrester devices
are continuously exposed to the combined e ect of distorted system voltage and envi-
ronmental thermal stresses. Recent studies supported by eld experiments have shown
signi cant rise in the leakage current through these surge arrester devices when exposed
to ac voltage with harmonics. However, the major shortcoming in the current knowledge
and applications of varistor arresters resides on the reliability and the electrical stabil-
ity of these overvoltage protection units, when subjected to long-term and continuous
distorted ac voltage and thermal stresses from the environment.
Commercially-sourced ZnO arresters of similar size and electrical properties are tested
using standard ac accelerated degradation procedure or electro-thermal ageing test. The times
to degradation, the coe cient of non-linearity, the reference voltages, as well as the
clamping voltage measured are used to analyse the reliability and the electrical stability
of the metal oxide-based arrester samples. The resistive component of the leakage current
is extracted from the measured total leakage current. The three-parameter Weibull
probability model is invoked in order to analyze the degradation phenomenon.
Description
A thesis submitted in ful lment of the requirements
for the degree Doctor of Philosophy
in Electrical Engineering
May 2016
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Citation
Bokoro, Pitshou Ntambu (2016) Degradation analysis of metal oxide varistors under harmonic distortion conditions, University of Witwatersrand, Johannesburg, <http://wiredspace.wits.ac.za/handle/10539/21153>