Calculation Method And Application Of Three-phase Voltage Unbalance

Nowadays,with the development of human civilization and the continuous progress of the power system,more and more energy is needed by society.One of the energy sources that can evaluate the development of society is the widely used electrical energy.High-quality electrical energy plays a major role in the stable work of power system equipment and the maintenance of social order.Whether the three-phase voltage is balanced is a key criterion for evaluating power quality and an important indicator for evaluating the safety of power grid operation.Nowadays,in order to better produce and live,the scale of the power grid is gradually expanding,resulting in many unbalanced loads entering the power system.Coupled with the different power consumption habits of various users,the problem of unbalanced three-phase voltage is gradually revealed in the power system.In addition,some distributed power sources,such as solar energy,are intermittent and random when generating electricity.They are connected to the power system in a single-phase fonn,which makes the three-phase voltage unbalance of the grid more serious.The three-phase voltage unbalance has a considerable impact on the line losses of the power grid,and it also jeopardizes the normal operation of transformers and other equipment.This will cause a significant loss to the work of the power system,make the power supply unreliable,and also cause trouble to the users of electricity,greatly damaging their satisfaction with electricity consumption.It can be seen that the evaluation of three-phase voltage unbalance has obvious theoretical and engineering practical significance.At present,domestic and foreign scholars have obtained some achievements in the field of three-phase voltage unbalance,but the method applied is relatively simple,usually considering the use of electrical methods to calculate the three-phase voltage unbalance,ignoring the effectiveness of other subject methods.In addition,the method of calculating the unbalance of the three-phase voltage in the international standard requires a tedious measurement process to obtain the corresponding vector,and even if the corresponding power is obtained,it is more difficult to calculate in practice.Therefore,exploring a more convenient and appropriate three-phase unbalance evaluation method has become a problem that still needs to be solved.In view of the above problems,in order to effectively evaluate the degree of three-phase voltage unbalance,it is necessary to explore and select the evaluation method of three-phase voltage unbalance.Based on statistics,this paper establishes a new effective three-phase voltage unbalance evaluation system based on statistical methods.The system consists of a traditional evaluation module,a voltage stability module and a voltage qualification module to evaluate the voltage unbalance.In this system,the voltage unbalance rate is first calculated by the PVUR formula,and the traditional method is used to evaluate the voltage unbalance.In addition,in the aspect of voltage stability analysis,the three-phase voltage time series is regarded as three time subsequences by using the statistical method of strictly stability and weakly stability.Considering the stability of these subsequences,the voltage unbalance is analyzed.Three stability tests-DF,ADF,and PP tests-are also used to express voltage balance from the perspective of voltage stability.Finally,the system selects the Burr distribution that fits the three-phase voltage data well to fit the voltage data,and optimizes its parameters through two intelligent optimization algorithms-the multi-objective gray wolf optimization algorithm and the cuckoo search algorithm,and finally determines the Burr distribution is obtained,and the voltage qualified interval is obtained to further judge the balance of the three-phase voltage.The system uses statistical methods to successfully overcome the limitations of various electrical methods,effectively expanding the diversity of voltage unbalance assessment.The evaluation results show that there is a certain degree of three-phase voltage unbalance in the study area,indicating that the Burr distribution model and the time series stationarity test have a good effect in the field of voltage unbalance evaluation.The three-phase voltage balance evaluation method proposed in this paper can not only accurately improve the accuracy of voltage unbalance evaluation,but also improve the efficiency of voltage unbalance evaluation,break the inherent thinking of traditional methods,and promote the management,development and improvement of power systems.This article mainly has four innovations:first,a new voltage balance evaluation system based on statistical methods has been successfully established.The system consists of a traditional evaluation module,a voltage stability module and a voltage qualification module to evaluate and expand the voltage unbalance The diversity of the evaluation methods of the three-phase voltage unbalance degree.Second,a strictly stationary and weakly stationary random process is used to estimate whether the three-phase voltage is unbalanced by using three-phase voltage data as three time subsequences.Third,selecting the distribution of phase voltage data to evaluate the voltage qualification can better reflect the advantages of statistical methods,and for the first time,the Burr distribution with good fitting effect is used for voltage data fitting.Finally,two optimization algorithms,MOGWO and CS,are selected to calculate the parameters of the Burr probability density function.These two algorithms can reflect the accurate information of the three-phase voltage.The system method is simple and easy to use,and it is an effective method for evaluating the three-phase voltage balance.