Current Differential Protection for Distributed Transmission Lines using Low Sampling Frequency

Abstract

Current differential protection has been affected negatively by the distributed capacitive current of transmission lines. In order to solve the problem of distributed capacitance current of transmission line, the current differential protection in this paper is based on distributed parameters model of the transmission line. The current formula along with the transmission line is derived under this distributed parameter line model. The differential criterion is constructed with the current calculated from both ends to the set point. In order to improve the practicality of the criterion, the implementation of the differential protection is given under low sampling frequency. By adding a cubic spline data interpolation point at each sampling interval, the calculation of the set point distributed current under low sampling frequency is achieved. In order to improve the operating speed of current differential protection, the point is set at the midpoint of the line, and the magnitude of the current is calculated with a half data window absolute value integrals. The results show that the proposed novel current differential principle is not affected by the distributed capacitance current. It has obvious advantages compared with traditional current differential protection principle for the low sampling frequency requirement, fast action speed and the small amount of computation.