Digital Model And Application Of Frequency Dependent Parameter Transmission Line

Transmission line model plays an important role in the area of transient protective relaying. In this paper, the digital model of frequency dependent parameter is proposed by means of orthogonal projection method and Poisson sum formula, combined with traveling wave propagation theory, the traveling wave propagation digital equation can be deduced. Hence, the algorithm is obtained practical application of transmission line protection.According to function space projection theorem established the discrete time digital equation of the distributed parameter model and the frequency dependent model, however, the crucial technique lies in how to calculate propagation function and surge impedance coefficient. This paper made use of Poisson sum formula got recursive discrete sequence of propagation function and surge impedance, and then Prony algorithm fitted to zeros and poles form, this reduces the number of discrete sequence. Ultimately, traveling wave propagation translate to recursive calculation of few coefficients. Propagation function is applied to parameter model, through programming by Matlab, to complete the propagating traveling wave quickly calculation from one terminal to the other terminal on line. By existing protection device it can be achieved for the lower sampling frequency, the results between PSCAD simulation and practical datum show that, the maximum error is less than 1.4% when Ts is 0.1ms, and the maximum error is no more than 1% when Ts is 0.01ms.On the basis of a new traveling wave based on differential protective principle is proposed by employing the characteristics of current traveling waves for the frequency dependent parameter line model, fits for only fundamental component but the transient components. There are fixed propagation relations between traveling waves of terminals as the line is healthy or the fault is external, however, the relationship is broken for the internal faults. The protective criterion and scheme are established by this characteristic. The large amounts of PSCAD simulation tests show that the protective scheme and algorithm is simple with high reliability, security, speedy and sensitivity, and fits for the transmission line with non-linear boundary.Propagation function obtained from this algorithm can achieve the fast protection of transmission line. The tests by PSACD simulations prove that novel principle is correct and efficient. These principles and theorems are approved to be the foundation of ultra high-speed protective relaying.