Influence Of Composite Load Model On Power Grid Fault Analysis

Fault analysis calculation is the basis of power grid design,dispatching and planning.In recent years,with the rapid development of national economy and society,the proportion of special loads in the power grid is increasing,therefore,their impact on the safe and stable operation of the power grid is also increasing.At the same time,the mechanism of the influence of the load model on the transient stability calculation and short-circuit calculation is very complex,if the equivalent load model of a wide variety of widely distributed electrical loads cannot be accurately selected,it will inevitably lead to errors and bias between the simulation calculation results and the actual operation of the power grid,making it difficult to accurately understand the operating characteristics of the power grid and its development trend.In order to meet the challenges mentioned above,in this paper,the influence of high-speed railway traction load on the transient stability of power grid and the effect of the proportion of induction motor with composite load on short-circuit current are studied against the background of an actual large grid.Firstly,the traction load characteristics are studied on behalf of CRH2 in view of the deficiencies of the research on the composite load characteristics of traction substations.The working principle of high-speed rail is introduced and the working principle and control strategy of the converters are analyzed in detail.Moreover,the detailed simulation model of high-speed railway is constructed and tested based on different operating conditions,and the simulation results show the validity and reasonableness of the detailed simulation model.The foundation for the later work on modeling the traction load of high-speed railway and the analysis of the impact on power grid is laid.Secondly,a composite load equivalent modeling method for substations with traction loads is studied for the needs of large grid simulation calculation.Based on the analysis of the operation characteristics and load composition of the traction power supply system,a composite load equivalent model of high-speed railway traction load--the mechanism load model of "constant impedance parallel induction motor" is proposed,and the accuracy and practicability of the equivalent load model is also verified.Then,using the Hunan power grid as the background,PSASP is used to simulate the transient stability of Hunan power grid and analyze the effect of traction load of high-speed rail on the transient voltage stability of Hunan,which enriches the composite load model category of power grid simulation calculation for the special loads.The above traction load equivalent model structure is also the composite load model used for short-circuit current calculation in some provincial grids,in which the dynamic characteristics of induction motor load is the most important element in the dynamic characteristics of power grid load.Therefore,in this paper,from the mechanism of short-circuit current provided by the asynchronous motor in short-circuit current calculation,the influencing factors between them are analyzed systematically.Furthermore,a method for determining the equivalent proportion of induction motor in power system short-circuit current computation is proposed.Simulation results verify the effectiveness and superiority of the method.Finally,typical substations in different regions of a provincial power grid are selected for simulation and the influence of load dynamic model on the short-circuit current calculation in power system is studied,and it is suggested that the parameters of load model of each substation are determined according to the regional characteristics of load distribution in the short-circuit current calculation by zoning.This paper further improves the work related to load modeling and enriches the load model categories of power grid simulation calculation,which lays a good foundation for power grid dispatching,planning and design.