基于零模电流相关性的直流配电网单极接地选线方法

Single-pole ground selection method for DC distribution networks based on zero-mode current correlation

柔性直流配电系统最常见的故障是单极接地故障。发生单极接地故障后,系统出现故障极与非故障极电压不平衡的现象,对系统安全稳定运行产生威胁,对保护方案的快速性和可靠性提出很高要求。针对此问题,首先分析了柔性直流配电系统线路发生单极接地故障后的故障电流特征,然后验证了故障时线路两端零模电流分量的相关性,最后提出基于线路两端零模电流量相关性的柔性直流配电系统单极接地选线方案。该保护方案充分利用故障后系统固有暂态特征,无需利用边界元件构造边界特性。在实时数字仿真器(Real Time Digital simulator,RTDS)上搭建基于模块化多电平换流器(Modular Multilevel Converter,MMC)的柔性直流配电系统电磁仿真模型验证所述方案的有效性。结果表明该选线方案能够实现快速、可靠识别故障线路,且耐受过渡电阻、噪声、传输延时的能力强,不受交流侧故障影响。

The most common fault of a flexible DC distribution system is the single-pole grounding fault.After the occurrence of such a fault,the system will have voltage imbalance between the fault and non-fault poles.This poses a threat to the safe and stable operation of the system,and demonstrates the need for the speed and reliability of the protection scheme.This paper first analyzes the fault current characteristics of a flexible DC distribution system after a single-pole grounding fault,and then verifies the correlation of zero-mode current components at both ends of the line when the fault occurs.Finally,a single-pole grounding line selection scheme based on the correlation of zero-mode current at both ends of the line is proposed.This protection scheme makes full use of the inherent transient characteristics of the system after failure and does not need to use boundary elements to construct boundary characteristics.A modular multilevel converter(MMC)-based electromagnetic simulation model of a flexible DC distribution system is built on a real time digital simulator(RTDS)to verify the effectiveness of the scheme.The results show that the proposed route selection scheme can identify fault lines quickly and reliably,and has a strong capability to withstand transition resistance,noise and transmission delay,and is not affected by AC side faults.