Research On The Improved Algorithm In Current Differential Protection Of Multi-terminal Line

With the large scale of distributed power supply and the increasing complexity of power system structure,T or multi-terminal of distributed power plants(including wind farms)tie line,more and more appeared in the grid frame structure,the operation mode of the grid system are complex,which will lead to challenge the conventional system configuration of relay protection.Once the line breaks down,it is required to protect the fault in the shortest possible time and minimize the economic loss.Based on the calculation method of longitudinal impedance of transmission lines at both ends,an improved algorithm for differential protection of multi-terminal lines is derived.This is an algorithm that uses the power of both ends of the circuit in the malfunctioning circuit and as a function of the current,the maximum voltage difference between the two ends of the line between the two ends of the line is the ratio of the maximum voltage between the two ends of the line,and that is the ratio of the voltage to the end of the end of the line,and the voltage,the voltage,the current,and the line impedance are the electrical triangle balance,and it can be separated from each other,and it makes it possible to be able to distinguish between the areas and the areas outside of the area..Through a reasonable decoupling algorithm,the three-phase power transmission line has achieved the aim of reducing the electromagnetic coupling between the two phases,so that the algorithm can realize the function of phase discrimination.Because of the unique nature of the T or multi-terminal line,the problem with the traditional differential is that it has to be affected by the power of the circuit capacitors,and the algorithm has proven that the algorithm itself can avoid the effects of the capacitor current.Based on the current saturation of current transformer,the algorithm is used to verify that the algorithm has a certain reliability margin when the current transformer is saturated.This paper simulates the high-voltage multi-terminal transmission line model of distributed contact line in ATP-EMTP,and carries out statistical analysis on the simulation data in combination with MATLAB.The results show that this algorithm has good state discrimination ability,simple setting,large discrimination margin and high reliability,and can effectively resist the adverse effects of line capacitance current and current transformer saturation,which has a good prospect of project promotion.