基于直流断路器动作响应的环状柔性直流配电网后备保护方案

A Backup Protection Scheme Based on the Response of the DC Circuit Breaker Tripping for the Meshed DC Distribution Networks

直流配电网由于供电能力强、线路损耗小、电能质量高等优点,已经成为未来配电网的发展趋势。柔性直流换流器过载能力差,且直流线路故障时,换流器直流侧电容向故障点提供数值很大的放电电流,对环状直流配电网继电保护的快速性和选择性提出了极高的要求。此外,一方面直流故障电流分断困难,技术尚不成熟,直流断路器存在拒动风险;另一方面,即使换流器闭锁后,仍然需要继电保护识别故障位置并采取故障隔离措施,以保障重启动和恢复过程的顺利进行,因此环状直流配电网的后备保护也应得到足够的重视。提出一种基于直流断路器动作响应的环状柔性直流配电网后备保护方案,分析了直流故障线路一侧断路器拒动情况下,相邻非故障线路上限流电抗器的电压变化特性,提出基于直流电流二阶变化率的故障识别判据和故障隔离方案;其次,分别考虑了高阻故障和故障线路两端直流断路器非同期分断等问题,提出基于直流电流一阶变化率的辅助判据和基于电流二阶变化率数值和方向的闭锁判据,以提升后备保护方案的整体性能;最后,基于PSCAD/EMTDC平台搭建电磁暂态仿真模型,验证了所提方案的有效性,结果表明:该方案动作无需通信,耐过渡电阻能力强,不受交流侧故障影响,能够在直流断路器动作后快速启动并为柔性环状直流配电网提供有效的后备保护。

DC distribution networks have become the development trend due to advantages of large power supply capacity,small loss and high power quality.However,the overload capacity of the converter is poor and the discharging current of the converter equivalent capacitor is large when a DC fault occurs,which puts forward high requirements for the rapidity and selectivity of the protection.In addition,DC circuit breakers(DCCBs)may fail to trip due to its difficulty in breaking DC fault current,and the protection is still needed to identify and isolate fault even after the converter is locked to ensure the restart and recovery of the system.Therefore,the backup protection for the meshed DC distribution networks should be paid attention to.This paper proposes a backup protection scheme for the meshed DC distribution networks on the basis of the transient DCCB tripping.When the DCCB on one side of the fault line fails to trip,the characteristics of the reactor voltage change rates on the non-fault lines are analyzed,and the fault identification and isolation scheme based on the DC current second-order change rates are proposed.Secondly,considering high resistance fault and asynchronous tripping of DCCBs,the additional criterion and locking criterion based on the DC current first-order and second-order change rates are proposed,respectively.Finally,the effectiveness of the proposed scheme is verified with PSCAD/EMTDC simulations,indicating that the scheme needs no communication and is unaffected by transition resistance and AC side faults,which can start quickly after the DCCB tripping and provide effective backup protection for the meshed DC distribution networks.