Detection Technique Research Of Single-Phase Break Line Fault For Distribution Line

As an important part of the distribution network operation, distribution lines can achieve the distribution of power but is very fragile at the same time. Any improper operation from staff as well as destruction from the outside world, may have resulted in large-scale power outages, and even cause the collapse of the power grid, and consequently bring about serious consequences for social economy and people’s life. Therefore, it is extremely important to carry out the distribution line fault detection for timely finding out the fault, restoring system normal power supply, maintaining the distribution network’s security and stability.There are a lot of researches on the transmission line fault detection at home and abroad. People put many manpower and financial resources, and equip with comprehensive protection devices for rapid detection, removal, fault isolation to protect the transmission grid security and stable operation. For fault detection of distribution lines, people focus more on various types of short-circuit fault detection and location. But to the break line fault, it has not received enough attention because the feature is not obvious. Therefore, maintainers will be short of related experience, and it often delays the accident and hazards safe operation of the grid.In order to response to the development requirements of smart grid and improve distribution network reliability, this paper treat the traditional distribution lines and distribution lines containing distributed power as the research object, achieve high sensitivity fault detection of single-phase break line fault. The main contents include:For 10 kV neutral ungrounded overhead distribution lines, use symmetrical component method to analyze each sequence component and each phase component in the relay location of current and voltage in the case of single-phase break line fault, single-phase break line plus power side ground fault and single-phase break line plus load side ground fault, and summarize electric parameter change characteristics of the corresponding fault conditions to provide a theoretical basis for protection criterion selection in the single-phase break line fault.According to the fault analysis results, when single-phase break line fault happen, the negative sequence current change on the fault line is greater than or equal to the positive sequence current change, and can be able to clearly distinguish with the fault line. It can be used as a single-phase break line fault protection criterion, but the sensitivity is not high enough. In order to improve the sensitivity of break line protection, the paper firstly use Hilbert-Huang Transform method to extract the second order intrinsic modal function IMF2 that is significant from negative sequence current, then obtain instantaneous amplitude of IMF2, calculate the summation of sampling value in m cycles and consider the amount of change as criterion to achieve high sensitivity fault line selection.Access of distributed power will affect the distribution power flow, and may lead to the result that the original fault line selection approach is no longer applicable. In order to solve this problerm, firstly, change the distributed power sources to a analysis model, and then establish 10 kV overhead distribution network containing distributed power, finally, analyze and summary the variation characteristics of all the electric parameters in the relay location after single-phase break line fault. The results showed that the negative sequence current before and after fault changed significantly, which can be used as protection criterion for distribution lines containing distributed power after single-phase break line fault, but the sensitivity is not high. Therefore, the paper propose that use Hilbert-Huang Transform to process the negative sequence current digitally, extract the second order intrinsic modal function IMF2, calculate the instantaneous amplitude of m cycles before fault and after the moment of fault after 7 cycles, and then choose the amount of change of the instantaneous amplitude as protection criterion to achieve high sensitivity fault line selection.When the single-phase break line fault occurring in the case of traditional distribution lines or distribution lines containing distributed power, use the negative sequence current together with the second order intrinsic modal function of negative sequence current to select fault line, which is verified by PSCAD/EMTDC and MATLAB. The simulation results show that, whether the traditional distribution lines or the distribution lines containing distributed power, this method can correctly and effectively select the fault line. The propose applies to traditional distribution lines and distribution lines containing distributed power. At the same time, it has high reliability, good sensitivity and important practical significance.