Research On Stochastic Estimation And Economic Assessment Of Voltage Sag

With the rapid development of science and technology,the sensitive equipments are widely used in lots of areas.Voltage sag is the main cause of sensitive equipments failure,which leads to huge economic losses both on power system side and consumer side,resulting in adverse social impact.Voltage sag is usually caused by the short-circuit fault of line,with strong randomness.Therefore,the assessment of distribution of voltage sag in power system and economic losses are instructive to the improvement of power grid and the selection of the mitigation device for consumer.First of all,to understand the existing stochasitic assessment methods of voltage sag deeply,different methods are reviewed.In addition to introduce the principles of stochaistic assessment method of voltage sag,this thesis also compared the advantages and disadvantages of different methods,which made the foundatioan for the following study on putting forward an improved method.On basis of cognition of stochasitic assessment methods of voltage sag,in views of shortage of the traditional Monte Carlo method in the stochastic assessment of voltage sags only takes the influence of the length of line on the line failure rate,therefore,an improved Monte Carlo method is proposed in this thesis to assess the systems' s voltage sag problems.Firstly,a probability assessment system of line fault is established considering the line's properties and objective effects.Secondly,the probability model of the short-circuit fault state variable is established by combining the assessment system.The IEEE-30 system simulation model is then established on PSCAD/EMTDC,the random numbers module and Multiple Run component are used to simple and send the fault information.The probability distribution of voltage sag characteristic variable and evaluation index of the sensitive load access point are obtained through multiple sampling simulations.The simulation results show the improved Monte Carlo method is closer to real condition of system compared with Monte Carlo and prove effectiveness of this method.In order to analyze the influence of voltage sag to consumer according to the power system sag information,this thesis considers the probability distribution of the uncertain area of consumer's voltage-sensitive equipment,the assessment results of influence on consumer caused by voltage sag are then obtained.This thesis also presents a cost-effective method for the consumer to the selection of voltage sag governance ways.And technical and economic assessment study on the sensitive load access point of IEEE-30 system is discussed with the application of NPV method.In order to solve the shortcoming of the existing methods without considering the actual industrial conditions,the thesis puts forward the method of assessing the probability of process fault based on the condition of equipment connections.The proposed method has better value in terms of accuracy and application.