扩大单元接线发电机定子接地保护方案

指出现有定子接地保护应用于扩大单元接线方式发电机上的不足，提出基于零序方向元件的选择性定子接地保护方案。采用发电机机端零序电流、接地变压器二次侧电流以及发电机零序电压构造零序方向元件，零序方向元件的动作边界可灵活整定，能够准确判断发电机区内、区外单相接地故障。该方案已应用到微机型发电机保护装置中，现场模拟试验结果证明了该方案的有效性和可靠性。

Study on Stator Earth Fault Protection of Generator Connected as Expanding Unit

A novel selective stator earth fault protection based on zero-sequence direction element is proposed, which can overcome the shortage of stator earth fault protection applied to generator connected as expanding unit. In the proposed algorithm, the zero-sequence direction criterion is calculated with zero-sequence current of generator terminal, the secondary current of neutral earthing transformer and zero-sequence voltage of generator, and its operating border can be set flexibly. The presented criterion can differentiate between a network earth fault and a generator stator earth fault exactly, which has been realized in digital generator protection. Experiment results show its validity and reliability.