Microcomputer Distance Protection And A New Algorithm Of Realization

Distance protection is the one which is influenced less by network structure and operation mode of the power system. It is the main protection mode of high voltage transmission lines in complex electric network all along.In computer distance protection, the protection generally selects fault lines first and then measures and computes electric quantity, i.e., phase selection methods are based on the idea of phase switch. The realization of phase selection is always based on software, that is, special programs are put up to distinguish the fault types and fault phases. This measure can ensure devices correctly switch off the fault phases and keep away from influence of the non-fault phase.At present, classification faults is mainly based on the methods of difference of phase currents integrated with symmetrical sequence components, the algorithms of Fourier transform analysis or solving differential equation. These two algorithms have their excellences, but also have drawbacks that response speed is slowly and computational accuracy is low. With the development of technique and the raised requirements to power system, it asks that the algorithms dealing with voltage and current data can select fault phases more nicety and quickly.This paper presents a new method to classify shorted faults. It analyzes the relative merits of distance protection theories and algorithms, and the methods for shorted fault phase selection in being. This paper puts forward a precept using transient energy to locate the fault phases and based on transient currents' characters brings forward the phase selection criterion. In this paper, a simulation mode for 500kV ultrahigh voltage transmission lines is made by Matlab6.5 Simulink, by which many simulations of shorted faults are done that are used to analyze phase selection algorithm. Simulation data verifies the reliability of the method. Besides that, a comparative study of wavelet transform algorithm and the Fourier transform algorithm is also done. The results prove that the convergence rate using wavelet transform algorithm is faster than that of Fourier transform algorithm, this can reflect on the time of fault determination.This paper raises a scheme realizing phase selection algorithm in hardware and software. The TMS320VC5402 of TI is used as central processing unit (CPU). The function of phase selection of distance protection is finished through modularization design.With the development of power system, the appearance and applying of new technologies, the requirement to reliability and rapidity of protection is raised. This paper can provide certain groundwork and reference for the realization of new theories and algorithms used in computer distance protection.