Research On Coordinated Protection Of Overcurrent And Overvoltage In ±10kV Ring Four-terminal VSC-DC Distribution System

Multi-terminal VSC-DC distribution system has become one of the key technology routes to build a new type of power system with new energy as the main body in China because of its advantages such as gird integration of renewable energy.Different topologies can be adapted to different application scenarios,and the ring topology is more suitable for a large scale of multi-terminal VSC-DC distribution system due to its advantages such as good scalability.However,there are few studies on the electromagnetic transient characteristics of ring multiterminal VSC-DC distribution systems under faults at home and abroad.The coordination and optimization of current limiting scheme,overvoltage protection scheme and relay protection action of ring multi-terminal VSC-DC distribution system under various faults is the basis of equipment selection and one of the key technologies to ensure its safe and reliable operation.This article mainly focuses on the generation mechanism and propagation path of overcurrent under bipolar short circuit faults,the design method of current limiting scheme,the influence of new load access on the current limiting scheme,and the interaction and coordination optimization of current limiting scheme,overvoltage protection scheme and relay protection action in the ±10k V ring four-terminal VSC-DC distribution system.Firstly,based on the system topology and parameters design,the electromagnetic transient simulation models of the ±10k V ring four-terminal VSC-DC distribution system are established in PSCAD/EMTDC,and the steady-state operation characteristics of the system are analyzed.Secondly,the mechanism and propagation characteristics of the overcurrent of the system under the bipolar short circuit fault are analyzed.And combined with the breaking capacity of DC circuit breaker,the design method of current limiting scheme and two specific current limiting schemes are proposed,which are suitable for the ring topology.And the influence of new load access on the original current limiting scheme of the system is studied.On this basis,taking the current limiting reactor scheme as an example,the influence of the current limiting scheme on the system overvoltage is analyzed,and the arrester configuration scheme and the switching impulse withstand voltage at each key position of the system are proposed.In addition,the differences and reasons of overcurrent before and after the system is equipped with arresters are compared and analyzed,and the influence of arresters on the transient current of the key equipment and the current limiting scheme of the system is proposed.Finally,the influence of the current limiter on the system relay protection action is analyzed,and then the overcurrent and overvoltage coordinated protection method of the ring multi-terminal VSC-DC distribution system is proposed.This article comprehensively considers the mutual influence and coordination optimization of the current limiting scheme,overvoltage protection scheme and relay protection action.The research results can provide references for the research of overcurrent and overvoltage protection schemes for ring multi-terminal VSC-DC distribution systems.