Study On Selective Leakage Protection System Based On Natural DC

The selective leakage protective system can give out alarming signal or cut off the fault branches selectively when the leakage fault happens, and the non-fault branches are working normally. It can reduce the power-off range and be facilitate to look for the fault, shorten the power-off time, and raise the reliability of power distribution.Firstly this paper has analysed the principles and deficiencies of existing selective leakage protective systems used in undergrounding low- voltage distribution network. The principle mainly includes the size of zero sequence current and the direction of zero sequence current . Then it studied the selective leakage protection based on natural DC in the un-grounding system, based on the simulated circuit of insulated resistance and distributed capacity of un-grounding distribution network, the principle of selective leakage protection based on natural DC was analysed in this paper.The main job of this research is:(1) the situation of one-phase leakage of one branch distribution network was analysed. And the process of building the math models of the measured current and leakage current was discussed separately in three parts of one periods. The relationship between detected current and leakage resistance was also discussed.(2) the situation of one-phase leakage of two branches distribution network was analysed. And the process of building the math models of main current and the current of leakage branch and current of non-leakage branch and leakage current was discussed separately in three parts during one period. The relationship between measured current and leakage resistance was also discussed.(3) Programs are made according to the characteristic of matrix operation and exporting figure of Matlab. The wave forms of detected currents under different leaking states in single branch and two branches distribution network was analysed. And the selectivity was expounded.(4)Through analysing the experimental data, the exactness of theory analysis was proved.(5) Finally the simple scheme of collecting data using computer and implementing their control using Delphi language was described. Although existing error and limitation in the experimental data. It was proved that the study of natural DC selective leakage protection is valuable no matter in theory or in fact.