A Permanent Magnet Excited High Efficiency Synchronous Motor With Line-Start Capability

Permanent magnet excited synchronous motors have seen relatively little application in the industrial area except where their synchronous motor characteristics are of absolute necessity. This is mainly due to their increased size and higher cost as compared to conventional induction motors. Part of that can be traced to the fact that the magnet utilization in those machines is relatively low. That causes both relatively high amounts of magnets per output power (cost) and a larger than common motor size. Recent work at General Electric has focused on the question of improving the magnet utilization. This has resulted in the design, fabrication, and test of a 25 hp permanent magnet excited synchronous machine with line-start capability. The goal of this project has been to demonstrate a machine which combines higher than previously known magnet utilization, very high motor efficiency and line-start capability. The paper presented describes the design, manufacture and successful testing of this motor which achieved the prescribed goal within the frame size constraints of conventional motors. Particular emphasis is paid to the machine performance during start and during synchronization.