Method of Continuous Electrolytic Loop-closing for 30° Phase-angle Difference Line Based on Three-Level Protection of Distribution Network

With the continuous development of the distribution network automation technology, the primary and secondary integration technology standards and equipment are becoming more mature, the reliability requirements of the distribution network are further improved, the protection range is extended from the switch inside the station to the switch on the column outside the station or the ring network cabinet, and the three-level differential protection mode of "station+branch+boundary" is gradually promoted, and "three-level protection" comes into being. Under the three-level protection of the distribution network, each section and branch switch of the distribution line is a circuit breaker, which does not rely on the action of the switch in the station to realize the local short-circuit current removal. At the same time, the extreme difference is formed through the protection settings, which further reduces the fault judgment and isolation interval, and improves the power supply reliability. On this basis, the three-level protection is also an important premise to solve the continuous electrolytic ring closing of the 30 ° phase angle difference line at the contact point: for the line load transfer with 30 ° phase angle difference at the contact point, the "break before make" power outage mode is generally adopted, which will cause power outage to users and greatly increase the workload of operation and maintenance personnel. Based on the actual work, this paper first describes the distribution automation and distribution network three-level protection mode, introduces the three-level protection coordination mode and line switch action mode under different faults through typical structural lines, and then proposes a 30 ° phase angle difference solution loop method for distribution line contact points based on the distribution network three-level protection method. Finally, the correctness of the proposed method is verified through theoretical and practical analysis.