Dielectric breakdown simulations of an OLTC in a transformer

Abstract

Purpose – The purpose of this paper is to report on the simulation of an on-load tap-changer (OLTC) in a power transformer. During design and test of the electrical insulation the influence of the environment on the OLTC is normally neglected. The authors investigate how large these influences are. Design/methodology/approach – The environment of the OLTC is taken into account by modeling tap leads in detail as well as transformer windings. The electric fields are computed and resulting breakdown voltages are estimated by using the streamer criterion. The results are compared to the ones of an OLTC without transformer and leads. Findings – For the investigated typical example the influence of the transformer and the tap leads on the internal OLTC insulation is small enough to neglect them during design optimization and test procedures. Originality/value – New is the execution of a finite element simulation and breakdown evaluation of such a complex geometric structure as the complete system consisting of OLTC combined with tap leads and windings. Furthermore, standard design and test procedures used by OLTC manufacturers are justified.