Research On Centralized Protection Methods For Spot Network With Multi Low-voltage Sources Parallel Supply With High Penetration Of DERs

Supply reliability is an important index to measure the performance of the power system,which only pays attention to the outage with duration of over 3 minutes.However,with the rapid development of society,a huge loss of sensitive load has been caused due to the short outage,which has aroused the attention of various circles in society.Spot Network with multi low-voltage sources parallel supply(Spot Network)which has been utilized overseas is regarded as one of the most reliable and flexible power supply mode,which supports both access management and local application of DERs.But the outputs of each source could be unbalanced due to their different parameters,what's worse,there could be reverse power flow in one incoming line and overload power flow occurred in others,which affects the economy,security and stablility of Spot Network.Thus,Network protector(reverse power flow protection)is configured on the secondary side of transformer,which is aimed at faults on primary side and preventing reverse power flow.However,the traditional network protector could not adapt to Spot Network with high penetration of DERs,which restricts the development of them.Firstly,in this paper the law of power flow distribution in this mode with the connection of DERs was analyzed,which proved the inapplicability of the original network reverse power protectors theoretically;then a new method of reverse power protection for Spot Network with DERs was put forward based on the positive and negative sequence current difference and their power flow directions,which could make the new protector accustomed to the large output of DERs by accurately distinguishing the large output of DERs from faults on the upstream of Spot Network,which could both cause reverse power flow;Besides,based on fault characteristics of Spot Network,low-voltage bus protection and outlet protection were improved and entrance and DER protections and their setting criteria were put forward to establish a centralized protection system,which could reduce outage losses of loads and improve the reliability of system by accurate fault location and rapid fault isolation;Last but not the least,the centralized protection system was simulated to justify the validity of protection logics and the rationality of setting criterias,which laid foundation for the practical application.