IEEE 930-2004 pdf download IEEE Guide for the Statistical Analysis of Electrical Insulation Breakdown Data
1.Scope
Electrical insulation systems and materials may be tested using constant stress tests in which times to break-down are measured for a number of test specimens, and progressive stress tests in which breakdownyoltages may be measured. In either case, it will be found that a diferent result is obtained for each specimen and that, for given test conditions, the data obtained ay be represented by a statistical distribution.This guide describes, with examples, statistical methods to analyze such data.
The purpose of this guide is to define statistical methods to analyze times to breakdown and breakdownvoltage data obtained from electrical testing of solid insulating materials, for purposes includingcharacterization of the system, comparison with another insulator system, and prediction of the probabilityof breakdown at given times or voltages.
Methods are given for analyzing complete data sets and also censored data sets in which not all the specimens broke down. The guide includes methods. with examples, for determining whether the data is a goodfit to the distribution. graphical and computer-based techniques for estimating the most likely parameters ofthe distribution, computer-based techniques for estimating statistical confidence intervals, and techniquesfor comparing data sets and some case studies. The methods of analysis are fully described for the Weibulldistribution. Some methods are also presented for the Gumbel and lognormal distributions. All the examplesof computer-based techniques used in this guide may be downloaded from the following web site “http:/grouper.ieee.org/groups/930/1EEEGuidexls” Methods to ascertain the short time withstand voltage or oper.ating voltage of an insulation svstem are not presented in this guide, Mathematical techniques contained inthis guide may not apply directly to the estimation of equipment life.
2.References
The following publications may be used when applicable in conjunction with this guide. When the followingstandards are superseded by an approved revision, the revision shall apply.
ASTM D149-97a(2004) Standard Test Method for Dielectric Breakdown Voltage and Dielectric Strength ofSolid Electrical Insulating Materials at Commercial Power Frequencies.!
3. Steps required for analysis of breakdown data
3.1 Data acquisition
3.1.1 Commonly used testing techniques
There are two commonly used breakdown tests for electrical insulation: constant stress tests and progressivestress tests. In these tests a number of identical specimens are subjected to identical test regimes intended tocause electrical breakdown. In constant stress tests the same voltage is applied to each specimen (they areoften tested in parallel) and the times to breakdown are measured. The times to breakdown may be widelydistributed with the longest time often being more than two orders of magnitude that of the shortest. In progressive stress tests an increasing voltage is applied to each specimen, usually breakdown voltages aremeasured. The voltage may be increased continuously with time or in small steps. Other protocols, forexample impulse testing, may also be used. Breakdown voltages may be much less widely distributed withthe highest voltage sometimes only being 2% more than the lowest voltage.
Various international standards, e.g., BS 2918-2 and IEC 60243, give appropriate experimental proceduresfor constant and progressive stress tests. This guide is intended to provide a more rigorous treatment for thebreakdown data obtained in this way.
3.1.2 Other data
Breakdown data may also be available from other sources; for example, times to breakdown of the insula-ion in service may be available, Such data is generally much more difficult to analyze since the history ofeach failed insulator may not be the same (see 3.1.4), particularly as units that failed will have been replacedt may also be unclear how many such insulation systems are in service and hence what proportion of themhave failed. The techniques described in this guide are, nevertheless, appropriate for such data provided sufficient care is exercised in their application.
IEEE 930-2004 pdf download
PS:Thank you for your support!
