The Simulation Of Fiber-Optic Differential Protection Criterion For Power Cable

The paper is focus on the research of the optical-fiber differential protection that can adapt to the power system of urban mass transit. Feeding electric power with cables, high voltage level and short transmission lines are the characteristic of the power system of urban mass transit. When we only consider the principle of differential protection, the problem that the selectivity of power system relay protection is bad can be well solved by using differential protection in 35 (33) kV cables of urban mass transit.This paper analyzes the basic characters of general vector differential protection, sampled values differential protection, differential protection based on fault component vector and differential protection based on fault component sampled values in detail. In order to test the four types of differential protection, Differential protection modules used in PSCAD/EMTDC (Power Systems CAD/ Electromagnetic Transients including DC) have been designed. By which, the effect of using the four protection principle in the cables which is used in power system of urban mass transit has been simulated. The parameter of cables used in simulation comes from actual parameter in power system of urban mass transit. By digital simulation, the paper has investigated the action of protection criterion under the situation such as one-phase to-ground, two-phase to-ground short circuit in the lines and outside of the lines, and analyzes the influences made by transitional resistance on protection criterion. The result of simulation shows: General vector differential protection has high dependability, but it also has relatively poor effect on avoiding the influence caused by transitional resistance. The differential protection criterion based on fault component has obvious superiority on sensitivity and capability of avoiding the influence caused by transitional resistance. At the last of the paper, the existing capacitance current compensation schemes have been introduced. The conclusion, the compensation schemes based on steady state vectors method is adapted to the power system of urban mass transit, has been drawn. The effect of compensation has been substantiated by the result of simulation...