| Non-ground neutral system and arc-suppression-coil-ground neutral system are called non-direct ground neutral system. The study of the feed line protection and fault location is one of the main fields when non-direct ground neural system is used. Proved by practice, the protection based on conventional over-current principle can effectively fulfill the work of protecting the feed line. The Qinghai-Tiber railway is across the Qinghai-Tiber altiplano. Because of short of power sources in the altiplano, very long feed line of power distribution system have to be used when one of the substations is failed to operate, in order to guarantee the reliability and security of the power supply.In this paper, firstly, one or more lump equivalent capacitances are used to simply the distributed parameter model of very long feed line. A fault location method is proposed, and different models are used to determine the fault point, as that is different. Simulation results indicate that this fault locating method is effective for the single-phase-to-earth fault of very long line of power distribution system on condition that the solid or arc fault occurs.Secondly, the simulation model of very long feed line of power distribution system of Qinghai-Tiber railway is set up. The simulation results indicate that the protection based on conventional over-current principle cannot meet the requirements of sensitivity when it is used in the very long feed line of power distribution system.Thirdly, two novel protective principles are proposed in the paper by analyzing data of simulation, which based on the negative-sequence current and variety of load angle. And setting rule of these principles is discussed in the paper.Finally, on the basis of the advanced software and hardware technology, a protection, measurement and control system for feed line is developed to overcome the disadvantages in present protection.
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