Fast And Accurate Calculation Of Breaking Flow Based On Nonlinear Breaking Function

Static safety analysis is to analyze all possible accidents in the power system,and take corresponding preventive measures to adjust the system's operating status to ensure the safe operation of the power system.The automatic selection of the expected accident set is one of the main contents of the static security analysis.In this process,firstly,the approximate open-cut power flow algorithm is used to calculate all the expected accidents in the power system,and the expected accidents are filtered and sorted,and then the accurate open-end power flow calculations are performed in order from the highest to the lowest severity.Due to the lower accuracy of the approximate power flow algorithm,the shadowing may occur,resulting in mis-ordering of the expected accident.At the same time,the two power flow calculations will consume a lot of computing time.In this paper,the current open-cut power flow algorithm is studied in depth.It is found that there is a strong nonlinear relationship between node voltage and admittance of breaking branch when admitting the branch admittance of the system continuously,resulting in a relatively fast convergence rate.The emergence of problems such as slowness and low calculation accuracy.Aiming at the shortcomings in the breaking current algorithm,this paper presents a fast and accurate calculation method of breaking current,which can directly judge whether the breaking current of the expected accident meets the security requirements of the power system.The 3rd-order Taylor series expansion of the admittance of the breaking branch is used to represent the voltage of the power system node,and the concept of nonlinear breaking function is proposed.The nonlinear breaking function can improve the linear relationship between the node voltage and the parameter of the breaking function,improve the Taylor series convergence speed and the calculation accuracy.Applying the nonlinear breaking function to the complex network,the general expression of the nonlinear breaking function is deduced and proved.It is defined as the ratio of two linear polynomials,and the nodal voltage and application matrix inversion obtained by the general expression is calculated.The conclusion reached by the law is exactly the same.This general expression applies not only to the branch breaking simulation but also to the node breaking simulation.In this paper,it is found that when using the nonlinear breaking function to calculate the breaking current,different breaking factors are selected,and the Taylor series convergence speed and the calculation accuracy are also different.Therefore,the optimization study of the nonlinear breaking function,by determining the optimal opening factor,to obtain the optimal nonlinear breaking function,can further improve the calculation speed and accuracy of the breaking flow.In the traditional static security analysis,it is not only necessary to sort and sort the expected accident set,but also to perform accurate correction calculation,which has a great influence on the calculation efficiency.If the algorithm is applied to static safety analysis,accurate scanning calculation of the expected accident set can directly determine whether the predicted breaking current of the accident meets the safety requirements of the system.This article takes the IEEE 14-node system as an example to perform simulation calculations.The computational results show that the computational load of this algorithm is equivalent to the three DC power flow calculations,but its calculation accuracy is close to the iterative power flow algorithm.The maximum error of the voltage amplitude is less than 0.0120p.u.,and the maximum error of the voltage phase angle is less than 0.0136rad,which verifies the feasibility and application value of the fast and precise algorithm of the breaking current proposed in this paper.The algorithm can also be extended to the case of breaking multiple loops to achieve fast and accurate calculation of the N-k breaking current of the power system.