Application Research On Adaptive Technology In Distribution Feeder Protection

Distribution network is the part of power system which connects directly with the customer, and whose operation status is directly related to electricity’s security and reliability of the users. The settings of traditional distribution protection is calculated out off-line, and remained unchanged in the operation, and then makes big influence on the sensitivity and protection range of protection, which is the key issue affecting the performance of distribution protection. But adaptive protection can be calculated its setting online in real-time as power system operation and fault status changes, it is able to adapt to different kinds of changes in system as much as possible in order to improve validity of protection. Therefore the adaptive protection comes into being, which provide an effective way to solve the problem of distribution network protection.Firstly, research status of distribution protection adaptive protection and wavelet analysis are summarized in this paper, and the basic principles and settings calculation of traditional protection and present adaptive protection are introduced. And according to their problems, an adaptive current protection approach which based on fault component of two-phase current is proposed. The approach can adaptive system’s operation style and fault types, without judging the type of short-circuit, and it also can improve the sensitivity of protection.Secondly, the key point of adaptive protection’s settings calculation is how to calculate system impedance online in real-time, for which an approach of using complex Morlet wavelet algorithm to extract the fundamental amplitude in fault component of steady-state voltage and current is illustrated in the paper. Because of its specific time-frequency localization feature, the complex Morlet wavelet algorithm can effectively filter attenuated direct current component and non-integer harmonics, which Fourier can not. Based on simulation analysis, the stability and accuracy of complex Morlet wavelet algorithm is better than Fourier algorithm, and it is able to fully meet the real-time and accuracy requirements of adaptive protection setting calculation.Finally, this paper also analyzes the protection problems of distribution with distributed generators (DG). According to detailed analysis of protection impact when DG access to distribution, an adaptive current protection scheme which make distribution suitable with DG is proposed. This scheme is based on the system operation modes and topological structure, and gets its equivalent transform and Thevenin model of the network back against the protection firstly. Then the method of combining adaptive protection setting with communication technology is used to protect all length of lines, and then the selectivity of tripping problem of DG access to distribution can be solved. Simulation results show that the proposed scheme of current instantaneous protection is able to protect all length of the lines.