Resonant Grounding System Fault Line

The single-phase to earth faults are the most probable faults in resonant earthed system, which is about 80% in all faults. It is difficult to detect the fault line because of the weak current and unstable arc. In absence of a more reliable detection method, manual switching is still generally used to identify an earthed line in current supply enterprise.Therefore, fault characteristics of resonant earthed system are deeply analyzed in this thesis. A simulation resonant earthed system including trolley wire, hybrid transmission line and cable is established in MATLAB/Simulink environment. Based on the model, various fault types are roundly simulation analyzed. Four new fault line detection methods are proposed and their reliability and feasibility are validated by digital simulation. The main contents of the thesis are listed as follow:(1) Fault characteristic of resonant earthed system are deeply analyzed in this thesis, which is the theoretical basis of fault line detection research.(2) A magnetic-transient simulation system is established. Various fault types in the magnetic-transient simulation system are roundly studied basing on the model. Current and voltage characteristics are contrasted in different faults. The effect of fault closing angle and the transition resistance to the fault zero-sequence current and voltage are inducted, which provide a better base for perfect line detection method.(3) On the basis of correlation analysis fault line detection method, a new fault line detection method through PRONY algorithm that extracts transient characteristics of fault zero-sequence current is studied. The method's availability is simulation-proved, the method's merits and demerits are generalized and the optimization programmed to improve the method's reliability is put forward.(4) The practical application effect of detection methods are not ideal because they excessively depend on mathematic tool and ignore the system's nature characteristics. Therefore, a simulation after test method using the fault's nature characteristics to detect fault line is studied. According to the excitation signals, above method can be divided into two. One fault line detection method uses zero-sequence voltage as excitation signal to simulate fault zero-sequence current, while the other use zero-sequence current. (5) A fault line detection method using traveling wave detection is shown, the issue in two-phase CT fault line detection can also be solved through the method.(6) Several factors that affect upon the fault line detection accuracy are considered, several fault line detection methods by Extenics are effective integrated, a perfect resonant earthed system fault line detection method is set up.