Study Of The Fault Distance Measurement Method For Small Current Grouding System By Injecting Signal & Design Of The Signal Source

The high-voltage transmission lines take on an important task of carrying electric energy, which are the vitals of electrical power system. At the same time, it is significant that the fault point will be found out quickly and accurately not only to the timely circuit repair and the power supply with guarantee, but also to the safety and the economic running of the electrical power system. The dissertation first generally introduces the present researching and application situation of the domestic and international three fault distance measurement methods which exit now. They are transmission line impedance method and the fault analysis method and the traveling wave method. Then, the fault characteristics of the small current grounding system are explained. After the basic principles of these algorithms are specified, the relative merits of them are analyzed. The principle of the fault distance measurement for small current grounding system by injecting dual frequency signal are discussed from many aspects such as the method and the characteristic of the signal, the test of the signal, the method of the line select, the algorithm of the fault distance measurement, and the method of the fault location, etc. The task adopts this kind of principle, in which the signal injection is completed by the coupling between the power source and the PT. In this way, the wattless power of the test signal at the head spot of the fault is only needed to sample when the system fault occurs, which simplifies the measurement. This paper also analyzes the errors of the algorithm with arc extinguishing coil and user load in the system, and explains its practicability and feasibility. Afterwards, the signal injecting power source and the partial hardware circuit of signal detection are designed and analyzed in detail. Finally, the flow chart of the main program for the fault distance measurement control process and the flow chart of the subprogram for fault disposal are given. It is worthy to be presented that the transconductance amplifier in which exerts the bootstrap technology is adopted in design on the high-voltage input power source, and the measurement of the wattless power is done by using mixed analog-digital multiplier and double-rank active low-pass filter in design on detection circuit...