Chopped impulses for distribution transformers their importance for dimensioning and performance evaluation

Impulse tests on distribution transformers are requested by all main international standards as IEC, IEEE and ANSI. They are also adopted by most national standards and normative. These tests consists in the application of a sequence of impulses, including chopped ones, to evaluate the insulation withstanding of the equipment, mainly failures on paper and windings. Although the chopped impulses are of main importance in this evaluation process, there is a discussion in some countries considering removing them from the test sequence. This paper discusses the importance of the chopped impulses and how they aid in the evaluation of the transformer failure probability.