A Comprehensive Technology Of Fault Line Detection Based On Transient And Travelling Wave In Non-Effectively Grounding Neutral System

In China,non-effectively earthed neutral is widely used in medium voltage distribution networks.As in the single-phase ground fault occurs, it do not form an effective fault current loop.Single-phase ground fault allowed to continue to run0.5to2hours.To ensure the reliability of power supply.However, due to the non-fault phase voltage increases, the failure is easy to develop for multiple fault.Should therefore be taken as soon as possible measures to find out the fault line to avoid the failure expansion.Artificial pull path method greatly reduces the reliability of electricity supply by the line selection.Line selection principle based on the traditional steady-state because of its inherent defects, leading to low reliability of protection devices.Often mistaken election, drain on selected issues. Therefore, it is necessary to conduct in-depth study.Analysis shows that the small current grounding system single-phase ground fault, Rich in fault transient component failure. Principle of the transient component of the line selection and line selection principle based on the steady-state component compared, Regardless of system operation mode, the advantages of the neutral grounding modes, the obvious advantages.In this paper, the transient traveling wave signal generated by the point of failure in the single-phase ground fault line selection. The line selection principle of comprehensive utilization of the energy of the transient zero-mode current signal and the polarity of the current traveling waves. When a fault occurs, the fault lines in the transient zero-mode current signal energy is much larger than the non-fault line. Of the difference of the transient zero-mode current signal energy line selection criterion. According to the fault line phase epidemic wave polarity different fault line fault discrimination. Based on the above principle, do the following work:1. Small current grounding fault mode network structure. Transient traveling wave generation and propagation characteristics were analyzed. Changes in the grounding resistance, the system is running the way little effect on transient traveling wave component, Principle is still applicable.2. The principle of superposition the fault network is decomposed into a superposition of the normal operation of network and fault component network. Study the fault component network. Analysis of the role of the bus on the current traveling wave refraction, reflection. Come to the bus will not affect the current traveling waves polarity.3. Establish the mathematical model of the transient zero-mode equivalent circuit. Derive the transient zero-mode voltage, current mathematical expressions. Draw the underdamped, over the way of damping and the case of the metal ground zero mode current oscillation.4. Based on the size of the relationship of the transient zero-mode current signal energy, as well as the faulty line and non-fault line current traveling wave polarity differences. Comprehensive utilization of transient zero-mode current signal energy, power pop wave polarity line selection principle.5. The PSCAD establishment of a distribution network fault model, selecting device unit. Verified the feasibility of the method.