Sequence current component and its power direction-based improved protection for spot network with DERs

Spot network has very high supply reliability and it is beneficial for integrating distributed energy resources (DERs). In conventional spot network, all the feeders are the sole power source, providing unidirectional power to the secondary network. The equipped network protector prevents power flow from the network to the feeder, to protect the transformer against upstream fault. If there are amounts of DERs injected, excess power inside the network will lead to frequently mistrip of the protector because the cause of reverse power cannot be differentiated. This study presents an improved protection for spot network with high penetration of DERs. It is based on the sequence current component and its power direction. There are various positive and negative components when different types of fault occur at different locations. Based on the sequence current variation, the reverse power caused by fault or by DERs can be differentiated. Then the fault can be located by comparing the sequence power direction among feeders. Based on this theory, the sectionalized bus-bar protection is also discussed. The simulation results prove that the proposed method functions effectively on enhancing the penetration amount of DERs and improving the supply reliability further.