Design Of The Filter Circuit Of Injected Signal In Distribution System

There are a lot of applications using signal injected system in Distribution System. The filter circuit of injected signal is used in the various testing, protective and control equipments based on signal injected method. Its performance will directly determine the quality of the signal that the equipments get, which relates to the actual performance of the applications, even the success or failure of the applications. Therefore, it has great significance to improve for the detection, protection and control levels for the distribution network, and also to improve the reliability of power supply.However, in order to reduce the cost and the impact to the power system, the injected signal of signal injected method in Distribution System is so weak, that it’s very difficult to pick the signal up. There is no systematic exposition of filter circuit design ideas, no detailed design, analysis and experimental demonstration in existing literature and articles for signal injected detection.Based on the analysis of principle, characteristics, realization to the three applications of signal injected method, and the characteristics of the channel of Distribution System, we determine design purpose and various indexes of the filter circuit of injected signal first. Then we design a general-purpose filter circuit of injected signal using cascade method. Finally we use PSPICE simulation and experiment to analysis and testing the filter.The detailed research works include:(1) We analyzed and summarized the three main applications of the signal injected system in the Distribution System:choosing signal phase to ground fault line based on single injected method, the signal injected method for the measuring of ground capacitance and Power System harmonic elimination, signal injected method for islanding detection and islanding protection. We discuss the basic application principles, the realization in the power system, problems and solutions of the signal injected method in distribution network.(2) We classify the existing filter circuit, give each of them a analysis of its feature and then we make a selection. We show the elements of our filter circuits, including the four sub-units:low-pass filter circuit, band-stop filter circuit, band-pass filter circuit and amplifier circuit. Then we define the function, requirements and design specifications of the filter circuit and its various sub-units.(3) We designed Sallenkey low-pass filter, double T notch filter, Fliege band-pass filter and amplifier classification. And we also give a detailed analysis to Op amp power supply, the relationship with the virtual ground and circuit design, component selection in the design.(4) We use the data got from PSPICE simulation and experiment to validate the filter circuit we designed and make further analysis.There are three important applications of signal injected method in Distribution System. By the analysis of their basic principles, implementation method, problems and solutions, we get that the design and research of the signal detection circuit has very important significance. The PSPICE simulation and experiments show that the filter we design can strongly suppressed 50Hz frequency zero sequence current,4th and 5th harmonic current harmonic interference. And the ideas of the design to the detection filter circuit is clear, simple structure, and can be widely applied to various monitoring in distribution network that based on signal injection to which protect and control the power system. It has great significance to improve for the detection, protection and control levels for the distribution network, and also to improve the quality and reliable of power supply.