Abstract
In order to evaluate an appropriate level of AC test voltage for 1000kV transformers, it is nece-ssary to make an accurate estimation of AC V-t characteristics. For the level of impulse test volt-age, V-N characteristics are important to evaluate effects of impulse stress repetition. Since both of the characteristics are dependent on insulation structures and manufacturing processes of trans-formers, it is important to make accurate simulations on transformer insulation for reliable insu-lation data.
To obtain some of the basic data for 1000kV transformer test levels, long time AC V-t tests and impulse V-N tests of up to 1000 times voltage application were carried out on an insulation model simulating fundamental structure of shell-form transformers. The model is composed of a para-llel electrodes system with a compound structure of pressboard barrier and oil gap.
The tests showed the following characteristics: AC V-t characteristics of up to several ten days could be described by two lines, each representing short time and long time characteristics. V-N characteristics of lightning and switching impulse were expressed by relatively flat lines, which showed decrease in breakdown voltage by less than 10% after 1000 times impulse application.
