Research On Hierarchical Protection Of AC/DC Hybrid Power System

The traditional protection which is based on local information still takes the heavy responsibility of power grid security.However,there are the problems that the traditional back-up protection is difficult to set cooperation and may cause cascading trip under condition of heavy load transfer.And due to the advantages such as long transmission distance,low line loss,HVDC transmission system is widely used and the complex fault characteristics from AC/DC hybrid area bring more new challenges to traditional relaying protection system.With great development of smart substation in recent years,station-area protection and wide-area protection,which are based on multi-source information,have become a hotspot in the research field of relaying protection.In order to solve a series of problems in the traditional primary and back-up protection based on local information and adapt to the fault characteristics of AC/DC hybrid power system,it’s necessary to take efforts on hierarchical protection,in which the information level is based on local protection,station-area protection and wide-area protection.First,establish the HVDC system in PSCAD/EMTDC power system electromagnetic transient simulation software and take simulation test on it to find the effect of continuous commutation failure on AC protection.After analysis of existing construction models of station-area protection and wide-area protection,this dissertation proposes a new hierarchical protection construction model and take research on the construction model of hierarchical protection in AC/DC hybrid area.Then,this dissertation proposes the protection configuration of each level in hierarchical protection,and studies on the sequential coordination of every level’s protection.And proposes a countermeasure for the effect of the continuous commutation failure in converter transformer differential protection.Last,by analyzing several typical fault cases and simulation,prove that the hierarchical protection,which adapts to the AC/DC hybrid area,can solve the problems in traditional relaying protection system effectively,and the fault can be removed quickly and reliably.