Investigations of an EHV autotransformer tested with open and arrester terminated terminals

The Special Termination Lightning Impulse test was devised to insure that transformers are adequately designed for service conditions not presently covered by standard test procedures. Analytic studies and factory fests were made on an EHV transformer to show effects of this test on a particular design. Calculations predicted terminal and internal voltage responses to the new test and were verified by good correlation with the tests. Analysis of internal voltages indicate that the new test is meaningful for this particular transformer. Examination of terminal responses indicate that the clamping action of the arrester prolongs the voltage crest at the non-impulsed terminals.