| With the continuous development of social economy,science and technology,as well as the upgrading of electrical equipment,the requirement of quality for power supply is getting higher and higher.As one of the most serious power quality problems,voltage sag has become the focus of attention in academia and engineering because of its high frequency and great harm.Distribution network is directly oriented to power users,and the probability of voltage sag disturbance is far greater than that of transmission network.Therefore,it is very important to research related issues of voltage sag in distribution network.This paper takes the identification of voltage sag disturbance source and the comprehensive evaluation of power supply reliability with voltage sag as the entry point,the main research work is as follows:Firstly,the principle analysis and characteristics of several typical voltage sag detection methods in time domain analysis and time frequency domain analysis are summarized.The detection effect and detection law of multi-resolution singular value decomposition(MRSVD)method in voltage sag signal are studied emphatically by Matlab simulation.The function relationship between the first detail component after the decomposition process,the sag amplitude and the sag time is summarized.Secondly,the 10 k V distribution system model is built by the software of Matlab/Simulink.By simulating various disturbances such as line faults,large-capacity motor operation and transformer no-load input,the characteristics of voltage sag under different disturbance sources are analyzed.Combined with Y/Y0,Delta/Y0 and Y/Delta three typical transformer wiring modes in China's distribution network,the variation characteristics of voltage sag waveform after transmission through transformer are studied and summarized in detail.Thirdly,aiming at the identification of voltage sag disturbance sources,the principles of several typical methods are elaborated.Combining with the variation law of the sag waveform after transmission through transformer,the single and compound voltage sags that may occur on the high and low voltage sides of transformer in distribution system are partitioned concretely,and a kind of identification method based on FFT and shape based weighted dynamic time warping is proposed.And this method can identify the type of disturbance source and judge the fault phase of line fault disturbance.The feasibility of the method is verified by the identification simulation of high and low voltage side of transformer.The simulation results show that the proposed method not only makes the identification content more perfect,but also has an ideal identification accuracy,which can provide reference for engineering application.Finally,aiming at the comprehensive evaluation of power supply reliability,this paper combines the drawing methods of SCBEMA and IVSC curves with the generalized tolerancecurve of equipment,establishes the user voltage comprehensive tolerance curve by weighting method,and gives a weight calculation method based on energy loss,and then establishes the outage probabilistic 3D surface of industrial,commercial and residential users under voltage sag events.In addition,the specific process of power supply reliability evaluation considering voltage sag is elaborated,and the process is analyzed in detail through simulation examples.The simulation results show that this method can reasonably reflect the impact of voltage sags on different types of users,and incorporate it into the evaluation process in the form of revised indicators,which is an important supplement to the existing reliability evaluation system. |
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