采用电流突变量夹角余弦的直流电网线路纵联保护方法

直流线路的保护是多端柔性直流电网发展面临的关键问题之一。文中针对现有纵联电流差动保护存在的问题,提出了一种采用电流突变量夹角余弦值的纵联保护方法,它利用线路两端电流突变量计算夹角余弦值从而进行区内、外故障判断。区内故障时,线路两端电流突变量方向相反,夹角余弦值为负值;区外故障时,线路两端电流突变量方向相同,夹角余弦值为正值。保护方法采用改进电压梯度法快速启动,并利用正、负极电压比值来识别故障极。仿真表明,所提出的保护方法不仅可以可靠识别区内、外故障,同时具有较强的耐过渡电阻能力且不易受线路分布电容电流的影响。

Pilot Protection Method for DC Lines Based on Included Angle Cosine of Fault Current Component

DC line protection is one of the key problems in the development of multi-terminal flexible DC power grid. This paper proposes a pilot protection method based on included angle cosine of fault current component to solve the existing problems of the pilot current differential protection. The included angle cosine is calculated by using the fault current component at both terminals of the line to identify internal and external faults. When internal faults occur, the directions of fault current component are opposite, and the included angle cosine is negative. When external faults occur, the directions of fault current component are same, and the included angle cosine is positive. In the proposed protection method, the voltage gradient is used to rapidly detect faults, and the ratio of the voltages of positive pole and negative pole is adopted to identify the fault pole. The simulation results show that the proposed protection principle can identify internal and external faults reliably. In addition, the proposed method is able to respond to faults with high transition resistance and is independent of distributed capacitive current.