The Confidence Limit of High-Voltage Dielectric Test Results

The uncertainty of high voltage dielectric test results is emphasized. This uncertainty can be expressed by a suitable confidence limit. The best figure suggested is the standard deviation σ for all the possible results of a test. A method for the calculation of σ is reported. Four types of confidence limits are considered and values are reported on the basis of available data from Centro Elettrotecnico Sperimentale Italiano (CESI) and many other laboratories. The spread of the results is found to be higher than expected. A survey of apparent causes of the uncertainty is presented but a series of unknown factors must be assumed to justify the figures found. Examples of application indicate the usefulness of the knowledge of the confidence limits of the test results.