Synchronizing variable frequency drives for on-line transfer

In many industrial applications involving motors controlled by AC inverters, it is often necessary to transfer a critical load to an alternate power source. Transfer applications vary depending on many factors. Considerations such as load inertia, drive type, motor size, and the level of desired automation are important items that must be taken into account by the user. This paper presents various techniques of synchronized transfer for loads ranging from small draw roll motors to large extruder motors in the man made fibers industry. Understanding these techniques will result in reliable synchronized transfers and will help minimize problems that may be encountered.