Differential Protection Of Distribution Network Based On Fault Signal Synchronization

In recent years, Distributed Generation has been developed, more and more low-voltage short lines appear, the closed-loop operation mode is applied in distribution network, a number of voltage-sensitive equipments has been used. In these circumstances, traditional protection has been very difficult to meet the requirements of quick action. Differential protection can remove the faults on the full line quickly, however, its synchronization is complex and expensive, which restrict the development of differential protection in distribution network. So the study of economical and practical synchronization mode for differential protection is very significant.With the development of distribution network, differential protection has been used in some areas to meet the requirements of quick action, its synchronization mode contain sampling data modification, sampling time adjustment, clock checkout, synchronization mode based on the reference vector, synchronization mode on GPS. These methods are complex and expensive, which constrict the application of differential protective. Thus, according to the structure of modern distribution network, we should study a synchronization mode suitable to the application of differential protection for distribution network.This article will introduce the principle of differential protection and its basic component, compare its channel types and synchronization mode, analyze the application of differential protection in distribution network.Analyze the structural characteristics of the distribution network, considering that the length of distribution lines is short, put forward a synchronization mode based on fault signal, that is, mark the initial moment of the fault signal detected by the protection device on both ends, put this moment as a benchmark to achieve synchronization of both ends. Based on this synchronization mode, propose the Phase-differential protection project in distribution network. According to its action criterion and performance requirement, obtain the demand of synchronization error.The synchronization error is determined by fault detection method, sample frequency in device and the length of distribution lines. This article compares fault detection method used commonly, selects the current break arithmetic to detect fault, derives the formula of fault detection delay, obtains the relationship between detection delay and the parameters in formula. By modeling the distribution network, calculate the maximum delay time of fault detection, educe the requirement of sample frequency. At last, the simulation test about fault signal synchronization has been carried out, through the digital simulation analysis and static simulation test, verify its practicality in distribution system. However, because of time limit, works about field validity has not been implemented, which should been practiced in future.The synchronization mode based on fault signal, whose process need not depend on channel, can reuse the fiber channel. It only change the algorithm in microcomputer protection, do not increase the cost of device. Theoretical analysis and test results show that this synchronization technology can meet the requirement of differential protection in distribution network and be beneficial of differential protection to further generalization in distribution lines, it has very important meaning.