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. © 2021 Automation of Electric Power Systems Press.