Positive-sequence-fault-component-based blocking pilot protection for closed-loop distribution network with underground cable

- The protection is realized by RTUs, and fault can be isolated by cooperation of adjacent RTUs.
- State of RNCs and the uniform blocking signal sending principle is defined.
- Fault can be located by comparing the power direction of positive sequence fault component.
- It has high sensitivity and strong tolerance ability of transition fault resistance.
- The protection can meet the demand of both open and closed loop operation mode.

Closed-loop operation of distribution network has attracted more attention recently to improve supply reliability and adopt Distributed Energy Resources (DERs) friendly. Its protection is usually independent of distribution automation system (DAS). This article presents a blocking pilot protection method for closed-loop distribution network with underground cable, that can be accomplished by remote terminal units (RTUs) in DAS. First, operation value of RTUs is designed on the current variation after fault and the RTUs are synchronized automatically based on fault signal. Second, the power direction characteristic of positive-sequence fault component is analyzed when various short circuit fault occurs at different locations. Based on that, the state of Ring Network Cabinet (RNC) are classified into five types and uniform blocking signal exchanging rule between adjacent RTUs is designed. The fault can be located and isolated directly by cooperation of adjacent RTUs. The setting principle and the operation logic for the pilot protection is given and its performance is analyzed. Finally, simulation model based on PSCAD is constructed. The simulation results prove that this protection can locate and isolate faults timely on the premise of high sensitivity. It has strong ability of enduring fault resistance and it can fit closed and open operation mode.