Load-Carrying Capacity Research Based On Economy And Security Coordination

The power system operation is constrained by a multitude of factors,such as security,reliability and policy.As a result,the evaluation of load-capacity limit is always conservative,leading to the fact that line power flow is much lower than its bearing capacity.However,load-carrying capacity is bound up with the system's economy and security.A higher utilization is doomed to delay the upgrading and rebuilding of system,contributing to a low cost in equipment better economic gain.On the other side,the system is weaker in dealing with disturbances under a relatively higher utilization,which results in a poor security.In consequence,it is necessary to study the changing relationship of loading-capacity to security and economy.Research of load-rating is experiencing an unbalanced development around the world currently.In our country,constrained by traditional evaluation method only based on reliability,load-carrying capacity of transmission lines has not been made the most of,which is less than 50 percent of its designed level.Restricted by environmental factors,it gets harder to erect power transmission lines or get fresh investment.In this sense,re-evaluating transmission line capability limit and equipment usage situation with a modified method is the key to solve the problem,which is also an important objective of power transmission and distribution systems of the smart grid construction.On the basis of conventional security evaluation,a economy and security coordination method is put forward in this paper to evaluate the load-carrying capacity limit in this paper.Loads are allowed to get another increase after the calculation of traditional available transfer capability,during which process,security and economy are taken into consideration at the same time in order to evaluate the very capacity limit under the existing grid.Simultaneously,reliability evaluation method gets an improvement in this paper in order to solve the problem that Monte Carlo simulation takes a relatively long period of time to obtain a higher accurate reliability index.The combination of Importance sampling method and Discrete Latin hypercube sampling method is able to reduce the variance of the sample space and uniformly sample it simultaneously,which improves the convergence of Monte-Carlo simulation.This paper points out that,the combination of sensitivity analysis and linear programming in the process of overload correction is able to guarantee the solution optimality as well as improve the solving speed.Examples are presented to illustrate practicality and usefulness of the method put forward in this paper.The calculation results show that the computational efficiency improves significantly in the process of reliability evaluation and the load-carrying capacity limit also improves dramatically,which makes the most of transmission capacity.