Demagnetization Analysis of Additional Permanent Magnets in Salient-Pole Synchronous Machines With Damper Bars Under Sudden Short Circuits

To improve output performance of salient-pole synchronous machines, permanent-magnet-assisted salient-pole synchronous machines (PMa-SMs) that have permanent magnets (PMs) between the field poles were previously developed. The PM effect of increasing the output power and the terminal voltage has already been confirmed by finite element analysis (FEA) and experiments under steady states. In this paper, demagnetization in the PMs due to sudden three-phase short circuits is evaluated by FEA. The results show that irreversible demagnetization arises in the PMs of a PMa-SM with relatively smaller circumferential PM length. Effects of the PM shape and damper bars on the irreversible demagnetization are also investigated. The results show that making the PM shape a rectangle and adding damper bars on the outer surfaces of the PMs are effective to reduce the demagnetization, while increasing the number of the conventional damper bars is not effective.