Medium voltage autotransformer failures: Explaining the unexplained — Continuation of the story

When medium voltage autotransformer (RVAT) motor starters fail, also referred to as a Korndorfer starter, the results are almost always catastrophic, particularly ones in which there is no clear failure to the core or tap-to-tap but just layer-to-layer deep down in the windings. An offshore platform is used as an example to explain the techniques and to discuss site specific solutions that are based on recently developed switching transient analysis, sweep frequency response analysis and state-of-the-art EMTP simulation techniques. This paper will explain how the power system, interrupter, and transformer interact and outline the steps to solve this long-standing problem as well as present the newly applied solutions. Since implementation of these new solutions, no further failures have occurred.