A Study on the Reliability of Polyester Insulators Blended with Borax
Tracking is the main factor which limits the safe working electric stress of insulation in power system applications. Polymer samples have been tested in laboratory conditions according to ASTM D2303 on accelerated inclined plane tracking test. In this paper, a model based on improved Weibull statistics is proposed for estimating the breakdown time of polymeric insulating materials with borax. The confidence intervals of the Weibull shape parameter and the Weibull scale parameter are determined for the borax concentration values using the Weibull 7++ program.
Statistical analysis of oil insulation breakdown voltage
Liquid or oil insulation are widely used in electrical power apparatus. The breakdown characteristic of oil insulation is statistically analysed. In order to obtain adequate information, suitable statistical distribution function needs to be identified to map with breakdown voltage data set. In this work, breakdown test of oil insulation is carried out with certain ramp rate i.e. rate of rise of voltage. The experimentally obtained breakdown voltage data was mapped with normal and weibull distribution. The statistical distribution of data is adopted to obtain information about the breakdown characteristics of oil insulation. The normal distribution is used to estimate mean value, standard deviation, whereas scale parameter, shape parameter are estimated using weibull distribution. Skewness factor is estimated for normal distribution and is seen to be of non-zero value. This non-zero skewness represents asymmetric distribution of experimental data. Weibull distribution being asymmetric in nature fits well with the experimental data. The weibull distribution provides significant information about the breakdown mechanism as well as characteristic breakdown voltage magnitude.
Control of the homopause level
Abstract This paper reviews the hypothesis that internal gravity wave breaking in the factor responsible for upper atmosphere turbulence generation and control of the number density at the homopause level. Available data from Mars and Earth support the hypothesis, originally introduced by Lindzen, that breaking thermal tides are responsible for the necessary turbulence. The lowest-order, equatorially trapped, westward-propagating diurnal tidal mode is the primary cause on the Earth, and lower-order westward-propagating semidiurnal modes are the primary cause on Mars. The frequencies and vertical wavenumbers of the responsible modes determine the eddy diffusion coefficients; energy density is only indirectly involved by determining which modes can break. A general scale relationship between tidal heating and velocity amplitude can be used to assess the breaking potential of tidal modes, and is used here as the basis for arguing that the number density at the Martian homopause is likely to have been stable over much of geologic time. Difficulties with this approach arise in the cases of Venus and Titan because of their peculiar zonal winds. For Jupiter and Saturn, internal gravity waves generated by nontidal mechanisms probably control the homopause.