Research On Fault Line Detection In Neutral Indirectly Grounded Systems With Wavelet Packet And Actualizing With DSP Systems

In China, neutral isolated and Peterson coil grounded system are widely used in 6 kV~35kV medium voltage distribution networks. Single phase earthed fault is the common fault in this system. To detect the faulty feeder is difficult for the fault current is very small. When single phase earthed fault occurs, it is necessary to select the fault circuit quickly. But, from existing status of this field, it has not been done very well. This paper introduces a novel fault circuit selecting method, which utilizes wavelets packet transform to obtain useful fault transient components and based on DSP, proposes a feasible solution.This paper analyses the transient character of line fault when the neutral point connects to ground in different ways. From the angle of signal processing, the wavelet packet analysis theory is introduced to selecting fault, in which the fault character is not the steady signal but the transient signal. Judging by the different magnitude and direction of the wavelet packet coefficient modular maximum, we can select the single phase-to-earth line.The data from the example of typical small current grounding neutral system validate the feasibility of the algorithms. The simulation result shows that using Wavelet packet analysis to separate the character from the transient fault signals is an efficient way.High speed single chip digital signal processor (DSP) is the fast developing single chip computer in recent years, the typical one is the TMS320 family produced by the TI. This dissertation successfully developed a VLST digital signal processing single system, using TMS320F240 as its central processing Unit (CPU), finished the function of line-selecting of non-solid grounded networks.