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.
Migration, Labor Mobility, and Relocation Assistance: The Case of the American Indian
This article, an example of "indirect" program evaluation, utilizes a 1/100 public use sample of American households from the 1970 U.S. census to examine family welfare levels among three categories of Indian families: (1) nonmigrant families living in traditional areas of Indian population concentration; (2) families in areas not receiving relocation assistance through the Bureau of Indian Affairs (BIA); and (3) migrant families moving to urban areas with BIA relocation assistance. The article concludes that the population of migrants receiving relocation assistance has a substantially higher level of economic welfare in both absolute and relative terms and that earnings are the principal source of increased welfare. It is suggested that such assistance might be utilized on a wider basis to assist other migrating populations.