中文摘要：

Powerformer非全相运行时将在其中性点产生很高的位移电压，而其分级绝缘的特点使中性点附近成为耐受过电压的薄弱环节。因此，相对常规发电机而言为Powerformer配置专门的非全相保护更为必要。在分析非全相运行状态特点的基础上，提出了一种基于Powerformer机端零序电压和定子绕组负序电流的非全相运行保护方案。采用EMTDC建立系统仿真模型，仿真结果证明，保护方案将零序电压和负序电流配合使用，对系统非全相运行的识别能起到相互补充的作用，保护原理正确可行。

英文摘要：

When Powerformer runs in the condition of open phase, the neutral point is exposed to high over-voltage. The weakest part in the insulation system of Powerformer is the neutral side and the high over-voltage is a serious threat to the neutral point. Hence it is important to study the open phase protection for Powerformer. Based on the analysis of the characteristics of open phase operational state, a novel open phase protection scheme utilizing the zero sequence voltage of the terminal and the negative sequence current of the stator windings is proposed. A simulation model has been constructed using EMTDC, and intensive simulations have been carried out, which demonstrate that the protection scheme is correct and practical, and using the combination of zero sequence voltage and negative sequence current can improve the reliability of the protection.