Transient over-voltages during switching of korndorfer auto-transformer motor starters

Induction Motors are widely employed in industries to perform various mechanical tasks. In spite of many advantages, it has a major challenge of high starting current, which demands the need of Motor starters to limit the starting current. For Higher rating motors, Autotransformer Starting method also known as Korndorfer Autotransformer starter is used. It is widely used in industries from decades along with Air insulated switchgear combination in medium voltage (MV) range but it suffers from major issue of transient switching overvoltages generation during Switching of MV Vacuumm circuit breaker (VCB) which results in failures and sometimes flashover. Basic Details of Krondorfer autotransfor starter and its working is presented in below article along with its advantages and disadvantages. Overview of transient overvoltage and a case study of failure or flashover in MV Air insulated switchgear is mentioned along with its root cause of failure. Preventive measures to limit these overvoltage during switching of circuit breakers are also briefed in this article.