Simulation Research On Fault Line Detection For Non-Solid Grounded System Based On Integrated Method

Non-solid Grounded System is widely used in our country's medium and low voltage distribution network, with the reasons that fault current is weak, the system can still keep symmetrical and continue to provide power to the load while single-phase grounding faults occur and some other reasons. In distribution networks, single-phase grounding fault is the most frequent in all faults. However, the fault detection of Non-solid Grounded System when single-phase grounding fault occurs has never been effectively solved because fault current is weak and fault arc is unstable. This paper aims solving the above problem.Firstly, basic principle of non-solid system and steady/transient fault characteristics after single-phase grounding are introduced. Secondly, simulation model of non-solid system is built in the software of MATLAB and EMTP. Thirdly, three kinds of simulation including metallic grounding, high-resistance grounding and arcing grounding are done in Neutral Ungrounded Power System and Neutral Resonant Grounded Power System, basing on the simulation model and the methods of utilizing steady /transient /injection fault information to detect fault. Last but not least, the application scope, advantages and limitations of different line detection methods are analyzed.In order to increase the accuracy of fault line detection and utilize the advantages of different detection methods, six methods including zero sequence fifth harmonic current method, energy function method, transient zero sequence reactive power direction method, signal injection method, zero sequence reactive power method, zero sequence active power method are integrated as the criterions based on simulation results. Basing on fuzzy theory, fault membership function of every line and weight membership function of every method are built. Then, one index which is used for fault line detection is generated according to the integration of fault membership function and weight membership function. At the end, digital simulation of fault line detection by integrated methods based on fuzzy theory is done and demonstrates its validity and reliability.