Study On Electrical Calculation Method For Reducing Aperiodic Component

The measurement accuracy of protection relay is severly affected by the aperiodic and random high frequency components in the input signal. Fourier algorithm, as the most widely used algorithm in the microprocessor-based protection, is largely influenced by the aperiodic component. The R-L model algorithm can only be applied to the calculation of the impedance of transmission line. The traditional curve fitting algorithm has high precision and flexible data window. However, it is not widely used due to its large computation and unsatisfied results.The accuracy problems of Fourier algorithm and curve fitting algorithm are compared and analyzed in dissertation. Combined with the specific circumstances of 11 OkV and above transmission system, several kinds of electrical calculation methods for reducing the impact of aperiodic component are proposed. First of all, to make up the poor effect of the traditional curve fitting algorithm, which using linear methods to fit aperiodic component, an improved method based on the general quadratic curve to fit the aperiodic component is proposed. Secondly, to reduce the influence of the random signals, a factor of aperiodic component is introduced to an improved method. Furthermore, a method which can filter the aperiodic component is proposed. Finally, a constant decay time is used into an improved method, so its errors within a certain range of the decay time constant and its calculation amount can be reduced.The improved methods proposed in dissertation are analyzed by using MATLAB ideal signal examples and PSCAD simulated signals. The results show that these methods have different anti-frequency fluctuations ability, anti-interference ability and response speed, and they have higher accuracy compared with the traditional method. In order to achieve the purpose of reducing the impact of aperiodic component accuracy, the advantages and disadvantages of each method should be considered. Then, one of them alone or several of them in conjunction can be used in real power system protection.