| With the rapid development of science and technology, the electric power consumptionof industrial and agriculture rises sharply. The existing power grid can no longer meet thedemands of electric energy transmission. While the smart grid has been widely studied andbuilt by most countries, strategies for developing smart grid are work out by nationalrelevant departments. Online monitoring of transmission line is the requirement of grid inthe future, because statues of transmission lines will affect the transmission of electricenergy. As the online monitoring technology of transmission is a hot research point in theworld, many different methods are proposed.In this paper, the short, earth and open fault hasbeen analyzed at first. The application of wavelet transform in singular analysis has beenresearched and a fault detection algorithm based on wavelet transform has been designedsecondly. The hardware and software of online monitoring system has been designed at last.Main works of this paper are as follows.The model of transmission line, the change of current and voltage when fault happenand the transient and stable state have been analyzed. The feature of zero sequence currenthas been analyzed. The power transmission line faults were simulated with the Simulink ofMatlab. The result of simulation has been analyzed.In order to implement wavelet transform on computers, the discrete wavelet transform,the multiresolution analysis and subband filtering has been studied. An algorithm to monitortransmission status was designed on base of signal singularity analysis with wavelet theoryand the feature of zero sequence current. The algorithm has been proved by simulation onMatlab.The system design of the online monitoring system has been described. Thearchitecture of dual CPU based on TMS320F2812and S3C2440has been proposed. Thechips were selected. The schematics were designed. Software requirements were analysedbased on principle of software engineering. The software of signal process system based onDSP, communication system base on ARM and monitoring software based on Labview wasdesigned. The main flowcharts of software and codes are presented.The signal conditioning circuit, the implementation of wavelet transform based DSP，AD sampling and communication between DSP and ARM have been tested in lab. Thefunctions of system have been tested based on the fault signal produced by Simulation inMatlab. The result of testing proved that system designed can work effectively and stably. |
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