Research On Single-Phase-to-Ground Fault Location Algorithms For Distribution Networks

In all aspects of power transmission, distribution networks cover the most regions.At the same time, single phase to ground faults happen most frequently in distribution networks. Therefore, to find out the single phase to ground fault points in the distribution networks has the great significance in improving the reliability of power supply. In the existing location methods, the impedance methods based on unilateral information are the cheapest. However, the accuracy of the methods is not ideal, the three phase voltage and current can not be completely detected in the incomplete star connection lines and the fault section can not be recognized by unilateral information in the lines with brunches have brought great difficulties to these methods.This paper studies the neutral groundings, voltage levels and the types of the faults though theoretical analysis and simulation experiments. In conclusion: the key to improve the fault location accuracy is to improve the amplitude of the additional fault current. Starting from the perspective of changing fault type, the amplitude of the additional current can be improved by setting artificial grounding point, in order to improve the accuracy of the location method.After setting artificial grounding point, this paper studies the the loop voltage equation of the fault phase, and deduces the location algorithm taking one-phase voltage and two-phase current as characteristic quantities which can locate the fault point in phase A or C. This paper studies the the loop voltage equation of artificial grounding phase too, and deduces the location algorithm taking one-phase voltage and one-phase current as characteristic quantities which can locate the fault point in phase B.In lines with brunches, this paper defines the coefficient of determination, and analyses the range of it when single phase to ground fault happens in different sections,and studies the the loop voltage equation of the artificial grounding phase, and puts forward the fault section identification method and the location algorithm which use unilateral information only. They can locate the fault point in the main line. Then this paper studies the the loop voltage equation of fault phase, and puts forward the location algorithm which can locate the fault point in the brunch lines.The artificial grounding transition impedance is mainly decided by the fault current and the fault resistance. This paper set the minimum value of the fault current to maximum load current, and set the maximum value to the starting current of definitetime over-current protection, and puts forward the calculation method of the fault resistance based on the residual voltage. This paper list the equation of the fault current,artificial grounding impedance and the fault resistance using the node analysis method and Ohm’s law. The value of artificial grounding inductance calculated by the equation is reasonable.