Application of Equation of Light Shutting in Selective Protection Device

At present, power distribution of 10kV and 6kV users generally adopts the wiring mode of connecting incoming and outgoing lines (distribution transformer) through the busbar. When each circuit breaker is equipped with protection, protection operation mode of three-stage series protection is formed, including incoming line protection, bus tie protection and outgoing line (distribution transformer) protection. With the development of the industrial process, users’ load is growing day by day. In particular, some smelting and foundry enterprises adopt two-stage power supply mode of switching station/distribution room. When each circuit breaker is equipped with protection, a six-stage series operation mode is formed. The protection operation mode is more complicated, as there are facts such as short protection circuit, similar fault currents, and no time limit for quick-break protection (all 0 seconds). Conventional protection devices have no selective protection functions and cannot achieve in-situ protection of circuit breakers in 10kV line. Local failures of the outgoing line can easily cause override trip of the incoming circuit breaker or the upper-level circuit breaker, which expands the power outage range, reduces reliability of power supply, and causes outage of some unnecessary equipment, thus affecting normal production of enterprises. In view of the above problems, this paper proposes a power distribution terminal device solution with selective trip protection function to realize intelligent protection, monitoring and management of 10kV substation and distribution network, and achieve multi-stage series protection of 10kV substation and distribution line against override trip and shutting. In the event of a line failure, it is possible to achieve in-situ quick protection, automatic quick isolation of the fault area, and automatic quick power supply transfer in the non-fault area, thereby greatly shortening power outage time, reducing power outage range, and increasing power supply reliability.