This chapter discusses the use of the enlargement law in relation to geometrical and time differences between laboratory test and system services in assessing the reliability of insulation. The more accurately the performance functions of the breakdown voltage of the individual elements have been determined (bearing in mind the statistical criteria outlined), the better the description that can be provided of the overall performance of the composite insulation of a large apparatus. Only in this way is there any prospect of being able to estimate the performance of the breakdown voltage for service conditions for structures that are extremely complex in insulation-engineering terms, such as metal-clad switchgear or power transformers. In the future, the high-voltage engineer will have to work even more intensively with statistical methods.

Inspec keywords: reliability; high-voltage engineering; electric breakdown; power apparatus; statistical analysis; insulation testing

Other keywords: large apparatus; insulation reliability; high voltage engineering; composite insulation; enlargement law; breakdown voltage; statistical techniques

Subjects: Power line supports, insulators and connectors; Other topics in statistics; Insulation and insulating coatings; Reliability; Dielectric breakdown and discharges; Power apparatus and electric machines