Long Line Distance Protection Based on Fast Phasor Calculation Algorithm

Abstract

In the long-distance and extra high voltage transmission system, distance protection has been widely used. Distance protection needs to determine if a fault is internal or external to a protection zone by calculating fault distance between the relay and the fault point. In another word, quickly and accurately extracting power-frequency phasor from transient fault signals is one of the most crucial factors to distance relay protection. This paper proposes a line distance protection scheme based on Fast Phasor calculation algorithm. Firstly, the fault transient is analyzed and the accurate frequency components are obtained by using the Fast Phasor calculation algorithm. In practice, the compensation matrix in the frequency-domain is vulnerable to signals extracting accuracy and calculation speed, not meeting the requirements of protection application satisfactorily. For practical application, the distributed parameter model is implemented with Bergeron method, and the matrix of fault signals is approximated by FIR filters in the time-domain. The new method Fast Phasor calculation algorithm is based on matrix pencil method and a reduced order method is made use of in order to simplify the algorithm and thus the calculation efficiency is improved. Obviously, Fast Phasor calculation (FP) algorithm has an outstanding advantage over Least Squares Matrix Pencil (LS) algorithm and Fourier algorithm. As a result, accurate fault signals data can be acquired quickly and accurately. Then, fault location can be obtained by using conventional methods. In this paper, single-terminal electrical quantities are used in the proposed scheme. The proposed distance protection scheme is not influenced by data window as theoretical analysis shows, which can be verified by further PSCAD simulation. Three types of fault are simulated in this paper, including single-phase ground fault, two-phase ungrounded fault and three-phase fault. All the simulational results from different fault types demonstrate that the presented scheme in this paper has low computational complexity, high accuracy and high efficiency. Simulated results also show that this method is valid and is capable of detecting the faults occurring on the transmission line quickly and accurately. This distance protection scheme is of practicality and reasonability.