柔性中压直流配电网线路加速纵联保护

分布式能源蓬勃发展和城市直流负荷快速增长,进一步夯实柔性直流配电网在城市的重要地位.文中以四端柔性中压直流配电网为研究对象,针对架空线频发的瞬时故障,提出具有速动性工程需求的加速纵联保护方案.该保护方案由启动方案、重合闸后瞬时性故障判别、永久性故障类型和故障区域识别组成.为降低加速保护第1次动作造成的误动,设计启动方案用于避免干扰、断线和功率翻转等情况.直流断路器在故障后1～2 ms内启动跳闸,确保换流器中电力电子器件不受破坏且故障后不闭锁.重合直流断路器后识别为永久性故障时,利用重合后的电压电流故障信息,准确识别出故障类型和故障区域.在PSCAD上搭建四端直流配电网进行大量仿真测试,仿真结果表明所提加速保护方案可靠有效.

Accelerated Line Pilot Protection of Flexible MVDC Distribution Network

The booming development of distributed energy resources (DERs) and the rapid growth of urban DC loads have further consolidated the important position of the flexible DC distribution network in the city. This paper takes the four-terminal flexible medium voltage direct current (MVDC) distribution network as the research object and proposes an accelerated line pilot protection scheme with the engineering requirement of quickness aiming at frequent transient faults of overhead lines. The protection scheme consists of pick-up program, transient fault identification after reclosing, permanent fault type and fault area identification. In order to reduce the maloperation caused by the first operation of acceleration protection, the pick-up program is designed to avoid the conditions of disturbances, line-broken, and power inversion. The direct current circuit breaker (DCCB) starts tripping within 1~2 ms after the fault to ensure that the power electronics in the converter will not be damaged or blocked after the fault. When a permanent fault is identified after the DCCB reclosing, the voltage and current fault information can be used to accurately identify the fault type and fault area. Finally, a four-terminal MVDC distribution network is built in PSCAD to do a large number of simulation tests. The simulation results show the reliability and effectiveness of the proposed acceleration protection scheme.