Research On Assessment Method Of Equipment Sensitivity To Voltage Sags Based On Uncertainty Theory

With the improvement of industrial production automation,a large number of precision equipment with microprocessor and power electronics technology as the core have been applied,and these equipment are very sensitive to voltage sag while improving production efficiency.Voltage sag has become one of the main power quality problems affecting the normal operation of sensitive equipment,causing huge economic losses to power users.Accurate assessment of voltage sag sensitivity of sensitive equipment can be used to assess economic losses,quantify treatment needs and select suitable treatment investment strategies and technical solutions,which has important practical significance and theoretical value.In thi s thesis,by considering the characteristics of system voltage sag and the tolerance of the equipment toward the sag,the assessment method of voltage sag sensitivity of sensitive equipment is studied.Firstly,in order to reasonably analyze the uncertainty and establish the assessment model,this thesis analyzes and summarizes the system voltage sag characteristics and the tolerance of the equipment toward the sag.The definition and causes of voltage sag are described.Based on the historical monitoring data,the distribution of the values of the main characteristic parameters of voltage sag is summarized.According to the relevant industry standards and test data,the sensitivity of sensitive equipment and processes to voltage sag is described.Then,in order to solve the problems of complex analysis and tedi ous solution process caused by the inclusion of both random variables and fuzzy variables in the evaluation of the sensitivity of voltage sag,a method of evaluating the sensitivity of equipment voltage sag based on equivalent random variables is proposed.The fuzzy nature of sensitive equipment withstand capability is analyzed.the concept of equivalent random variables is introduced,and the affiliation function of equipment withstand capability is transformed into the equivalent probability density function.An evaluation model is established based on the mean first-order second-moment method using the mean and variance of the equivalent random variables.The simulation results show that the proposed method can not only reflect the severity of voltage sag,the influence of tolerance of the equipment toward the sag,but also simplify the solution process and improve the calculation efficiency.Finally,considering the transition process of equipment operating state when suffering from voltage sag and the influence of voltage sag type on equipment operating state,the method of evaluating the sensitivity of equipment voltage sag based on fuzzy event probability is proposed.The fuzziness of the equipment operating state and the influence of the type of voltage sag on it are analyzed,and the process is described by the subordination of the equipment operating state to the fault state.Based on the basic theory of fuzzy event pro bability,the possibility of equipment failure caused by voltage sag is quantitatively analyzed.Evaluation models are established for two different application scenarios: specific voltage sag events and node voltage sag prediction.The simulation results show that the proposed method can reflect the influence of the equipment operation state and the type of sag on the sensitivity of the equipment voltage sag.