Dielectric Tests and Test Procedures for EHV Transformers Protected by Modern Surge Arresters and Operated on Effectively Grounded Systems 345 KV Through 765 KV

The shortcomings of the existing standard dielectric test procedures for EHV transformers are stated. Proposals are made to correct the shortcomings. The proposals include dissociating the low-frequency test voltage requirements from the transient test voltage requirements, and relating each test independently to. corresponding operating conditions. Impulse and switching surge tests are related to the characteristics of the protecting surge arrester. Low-frequency tests are related to operating voltages. The duration of the low-frequency test is increased, and the magnitude is reduced. The trans former is connected, for the test, as it is connected in service. Continual monitoring of corona is recommended. The objective of the proposals is improved operating reliability by specifying tests which are more compatible with service requirements. Examples are given.