Analysis of the starting transient of a synchronous reluctance motor for direct-on-line applications

Current industrial trend shows a growing interest towards energy efficiency within industrial processes. In this field, electric motors play a paramount role. Traditionally, high efficiency applications have been satisfied through rare-earth (RE) permanent magnet (PM) motors run by a variable speed drive (VSD). However, also PM motors for direct-on-line applications have been manufactured for years, having though very special and limited applications as target. Due to the increasing cost of RE materials from one side and the intrinsic simplicity that lies in avoiding frequency converters on the other side, the attention has been focusing on the possibility to extend direct-on-line applications also to other synchronous technologies, such as synchronous reluctance, which is revealing its potential in terms of sustainability and environmental safety. This target is achievable by installing a squirrel-cage within the rotor, to enable asynchronous starting while preserving performances of the synchronous technology at steady state. The aim of this work is to report and comment starting tests on a synchronous reluctance motor (SynRM) for direct-on-line operation, in which the squirrel cage has been obtained by filling the flux barriers of a state-of-art SynRM with aluminum through a casting process. Related finite element analyses and comparisons with an equivalent induction motor are also included.