Study Of Adaptive Window Length Algorithm For Differential Equation Based On Noise-Level Control

For a long time , distance relaying protection had been widely used in the power system. Distance relaying protection requires an algorithm used in it to achieve accurate calculation and fast convergence in the impedance measuring. Fourier-transform-based algorithms has a fast convergence and good high-frequency characteristics, it is widely been used in the digital distance relay protection. But Fourier-transform-based algorithm also has its shortcomings, it has a long window size and can not eliminate the influence of the unperiodic component current. Thus it may delay the trip time. The differential equation based algorithm are not affected by the unperiodic component current. It has a short window size. And what's more, it is not affected by the fluctuation of the power frequency. But the differential equation based algorithms exhibit poor high-frequency characteristics so that significantly time-delaying filters are required.An adaptive window algorithm controlled by disturbance after fault was presented by the authors based on the 1st order differential equation after study of many used algorithms in relay protection. This new algorithm can break the limitation of the conventional poor high-frequency characteristics problems of fixed window length distance relay protection algorithm. When a fault occurs, the noise lever will be first caculated. Only after the noise lever being lower than a certain value dose the differential equation based algorithm begin to caculate. And the window size is fixed at a time which is between now and the fault start's time. If the noise lever is not lower than the certain value after 15ms for 3.3ms, the differential equation based algorithm will be automatically put into caculation, and the window length is fixed at 15ms. Thus the high-frequency characteristics of this algorithm is greatly improved and it also achieves a fast convergence. Besides, Automatically change the window length will not delay the trip time. This algorithm can make the the differential equation has a strong filter ability. And both accuracy and operating speed are satisfactory owing to the variable-window-processing technique. Relatively few computations are involved so that it really can be put into practical use.Extensive ATP testing has been conducted using the model of the 500kv power system and the results are presented to demonstrate the noise lever controlled window length algorithm's performance. The simulation data results of different type of fault...