The New Method Of Fault Line Selection Research The Small Current Grounding System

In China, distribution network generally adopt non-effectively grounding in order to avoid the power interruption causeed by the single-phase ground fault, and also to improve the reliability of power supply.For the single-phase ground fault in non-effectively grounding system, the fault current is small, and the failure characteristics is weak and vulnerable to the impact of environmental interference noise, these eventually lead to a error in judgement of fault line.In particular, the system which neutral point grounded by the Arc-suppression coil,because of the capacitive current is compensated, the amplitude of residual current at the point of failure is very small, and phase is also changed, so the fault line selection method based on steady state component of zero sequence current is no longer effective.The problem of fault line selection in non-effectively grounded system has been studied for years both at home and abroad, however,it still has not been resolved satisfactorily, which has seriously blocked the improvement of reliability of distribution network power supply and automation level.With the improvement of quality of power supply requirements, the technology of fault line selection in non-effectively grounded system becomes more and more prominent.Therefore, The technology of fault line selection which is accurate and reliable has great significance.In this paper,a detailed analysis of characteristics of the single-phase ground fault in non-effectively grounded system has been presented, especially,there is a discussion in deepth about single-phase ground fault transient in the system which neutral point grounded by Arc-suppression coil, and study the effect which produced by Arc-suppression coil for fault zero-sequence current under different initial angle of fault.In non-effectively grounded system,the amplitude of fault transient current is times or even several times than steady-state current, but the duration is very short and susceptible to interference.Thereby,the thesis proposed a novel algorithm to extract the principal component from zero-sequence transient current in order to avoid random interference signals and high-frequency transient oscillations, the principal component can reflect the main features and the overall trend of the transient current. The thesis using PSCAD/EMTDC simulation software to build a non-effectively grounded system simulation model, and construct a simulation model of the dynamic arc furnace by using the MATLAB interface in PSCAD/EMTDC based on numerical solutions of electric arc furnace dynamic characteristics of differential equations.On the basis of this platform, the compensation characteristics of the Arc-suppression coil, the fault characteristics of the overhead lines and cable lines and the nonlinear of arc furnace load have been simulated, a novel fualt line selection method based on the correlation analysis of SVD principal component which is extracted from zero-sequence transient have been proposed, and a large number of simulation results show that this fault line selection method has high reliability margin larger and anti-jamming capability.Based on the study of SVD algorithm, this paper also proposed a new method of signal singularity detection based on the SVD algorithm,the method is also applied to the fault line selection based on the direction of the zero-sequence current mutation detection technologies, a large number of simulation show that the method can correctly identify mutations direction of the zero-sequence transient current, and thus reliably.