Medium-Voltage Autotransformer Failures: Explaining the Unexplained—Continuation of the Story

When medium-voltage reduced-voltage autotransformer (RVAT) motor starters fail, also referred to as Korndorfer starters, 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, the results are almost always catastrophic. An offshore platform is used as an example to discuss site-specific solutions that are based on the recently developed switching transient analysis, sweep frequency-response analysis, and state-of-the-art electromagnetic transient program (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 the implementation of these new solutions, no further failures have occurred.