A new type of automatic bus transfer equipment with function of ring current protection — Research and application

The 10kV distribution grid operates under an ‘open-ring operation’ mode. To avoid disturbance in HV power system due to the ring-opening or ring-closing current, ring-closing switching operation is forbidden on the LV (400V) bus-bar in distribution room. So, when switching operation on the LV busbar occurs, the customer should always endure a blackout, at least for several minutes. To solve this problem, the feasibility of ring-closing switching operation on the LV bus-bar is researched, through the digital simulation and field test. On this basis, a novel LV automatic bus transfer equipment (ABTE) based on PLC is developed and applied to distribution room in Beijing. By real time monitoring and detecting the ring-opening and ring-closing current, the function of ring current protection is integrated into the traditional ABTE, including function of automatic transferring and automatic resumption. Thus the LV customers can be automatic transferred to a standby resource without outage. This LV ABTE has been successfully applied to distribution grid in Beijing.