| Neutral un-effectual grounded system is widely used in the distribution networks in China and other countries. It has the virtue of proving power supply's reliability. In the undercurrent earth system, the single-phase grounded fault is not big to electrical network's threat. Even if is the permanence single-phase earth fault, the electrical network still allowed the belt breakdown to move for 1～2 hours. When the neutral un-effectual grounded system has the single-phase earth fault, other two voltage magnification becomes the line voltage relatively. Even it leads to the intermittent arc light earth. Because the neutral point does not have the electric charge release circuit, it will cause the arc light earth over-voltage. The system insulation is destroyed. Therefore, It is great significant to select the fault line and clear the fault as soon as possible. The coefficient of single phase-to-ground fault is very high in NUGS, but the faulty current is so small that fault line selection problem has not been solved effectually as yet. We need to propose a new method to select urgently.The paper pays special attention to the transient procedure of peterson coil grounded system after faults. After the single-phase grounded fault occurs, the transient signal includes plenty of fault characteristics. The preliminary stage which occurs in the fault, the peterson coil may be ignored to the transition condition charging current's compensation. Therefore, we should find the transient signal includes plenty of fault characteristics as much as possible. It is important to enhance the route selection accuracy. Then it introduces the basic principle of wavelet analysis, multi-resolution analysis and Mallat algorithm. Special attention is paid to Wavelet analysis to signal irregularity examination principle.This paper proposed a faulty line selection method by using of Failure measure and wavelet transform that has local characteristic to pick-up transient information. When the electrical network has the single-phase earth fault, in this electrical network's each line including the bus bar is the object which suspected. Which is the fault line of a line needs to be judged according to their characteristics. Meanwhile, We hope to get the criteria to calculate each line in a fault line performance level of size. So we put forward the concept of fault measure. Firstly, transforming the post-fault transient component with wavelet, the fault line is found through comparing the magnitude and polarity of wavelet transform of zero sequence currents. Then we compute the calculation of the line (including bus) measure the value of the fault. Subsequently the comparison is conducted in the aspects of magnitude the polarity and fault measure. This method overcomes the defects of traditional fault line selection means, which will misjudge the fault line when the steady zero sequence current is very small. It is free from the fault resistance and the neutral grounding modes and can find the fault line reliability. A model of arc suppression coil grounded system is built combining the actual data in the software of MATLAB, and various of circumstances of single phase-to-ground fault are simulated and experimented.This paper briefly introduced the features and functions of fault phase selection device, and designed the hardware and software. The modular design method was used in hardware design. The data acquisition module and communication module were designed carefully. Because of the powerful and effective computing performance and the abundant interface circuit of ARMsth9 microprocessor used in the design, the signal processing ability was improved substantially, the complexity of external connection was induced greatly. In order to satisfied the communication requirement of the automation system, communication interface was set in the device. So the device can send phase-to-ground message and protection action message, or receive timing order.
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