Research On The Technology Of Single-Phase Grounding Protection For Boundary Switch Based Transient Signal In Distribution Network

With the rapid development of intelligent distribution grid, the power supply reliability has been greatly improved, the fault rate of trunk line in distribution grid has been rapidly decreased, and the user’s internal faults highlight. User’s internal fault may cause the blackout of whole distribution line, which will influence the normal power supply. Installing user demarcation switch in the user T junction in distribution line (intersection between main line and branch points) or end user’s incoming line can solve this problem effectively. In recent years, there is some research on demarcation switch protection based on the steady state detection technology, but the field operation is not effective. The main defect of using the steady-state fault signal to monitor fault is the steady-state fault component is small, which may cause the demarcation switch cannot be reliably operated. In arc-suppression coil neutral system with over compensation way, the zero modal current direction of fault line and healthy line are consistent and the zero modal current amplitude in fault line is smaller than that in healthy line, which may cause the miscarriage of demarcation switch.Based on analyzing steady state protection technology of demarcation switch, Guided by the fault line selection principle in non-effectively grounding neutral system, two demarcation switch protection schemes using transient signal are proposed. It can solve the problems of low sensitivity and poor reliability existed in the demarcation switch steady state protection technical.According to the obvious difference of the transient zero modal current amplitude between two sides of demarcation switch, the paper proposes demarcation switch action principle based on transient zero modal current amplitude protection and by comparing transient zero modal current amplitude with fixed value, internal fault or external fault is determined. According to the difference of transient zero modal reactive power in both sides of demarcation switch, the paper composes to demarcation switch action principle based on the transient zero modal reactive power direction protection, which determines the internal fault and external fault by comparing zero modal reactive power direction of the internal and external.By using EMTP-ATP, a simulation model of non-effectively grounding neutral system is built to verify the validity of two kinds of transient signal based protection technologies. Vast simulation in conditions of different transition resistance and fault location has been done to verify the effectiveness of the proposed technology about demarcation switch based on two kinds of transient signal protection. A static simulation experiment has also been designed in the laboratory to confirm the above two methods, which both proved their effectiveness and practicability. It is of theoretical and practical significance in promoting the research on demarcation switch based on transient signal protection.