A Study On Power System Thermal Security Region

The security and stability of power system operation is of vital importance to theprosperous development of national economy and harmony of social life. Recentlylong-distance transmission, regional grid interconnection, electricity market and newtechnology components are increasingly more, due to the rapid upgrade of power grid.These new situations make the operation of power system more and more complicate,and equipments of power system always work near their stability limits, thus theproblems of power system security and stability are more obvious. And the frequentoccurrence of large scale blackout in recent years is just the concentrated reflection ofsuch problems. Methods of power system security region have contributed to dealingwith the problems of power system security and stability, while the power systemthermal security region which meets the current constraints of all the transmissionlines is a kind of the basic power system security regions. This paper defines powersystem thermal security region in the decision-making space and studies the approachof fast calculation of thermal security region boundary.To begin with, this paper establishes the decision-making space based on thevariables of power system real time operation and presents the expression of powersystem thermal security region in decision-making space. Actually, thermal securityregion boundary which is within the engineering concern and limits of equipmentscan be approximately described by several hyper planes, and examples show suchfeasibility.Furthermore, a mathematic expression based on the AC power flow to calculatethe hyper plane coefficients of thermal security region boundary is derived fromTaylor series and sensitivity. To improve its accuracy, this paper also provides a fastcalculation approach of thermal security critical points, and obtains the hyper planecoefficients in a certain critical point. Examples show that the accuracy and thecomputation speed of the approximate boundary of power system thermal securityregion is significantly improved by the approach given in this paper.At last, concerning about that practical power system thermal security regionboundary consists of few lines’ thermal security boundary, a method to choose lineswhich likely exceed their respective current limits is give by decoupling AC powerflow model and tangent plane of hyper surface, such that it is possible to calculate thermal security boundary which takes all lines into consideration with lesscomputation burden.