Research On Emergency Control Strategy To Improve The Level Of Transient Voltage Stability

With the rapid development of science and technology, power system change a lot.For example, large capacity generators use generally, power systems are interconnected together, power grid voltage levels rise, load capacity is relatively concentrated, dc transmission and new type power electronic control device are applied and so on. But restricted by environment and construction cost, power grid structure is relatively weak, power generation equipments reserve less, systems often run under the condition of heavy load, modern sensitive loads have more proportion, the current situations make the voltage stability problem increasingly serious.This paper bases on: optimization of dynamic reactive power compensation device of Guangdong power grid. It deeply studies transient voltage stability and emergency control measures. Transient voltage emergency control is a control way after the accident. When the power system is under a state of emergency, by taking appropriate measures, make the electric power system return to normal or restore state temporarily. Common improvement measures have two kinds: one kind is dynamic reactive power compensation device represented by static synchronous compensator, another kind is emergency load control. Build optimization model respectively firstly. Then considering voltage stability constraints and the min cost of control, control the reactive power compensation and emergency load cooperatively to improve the probability of voltage sag. In this paper, main work is as follows:First of all, considering the transient voltage security, emergency load optimization control model is put forward. Use the cost of control as the single objective function. Introduce the trajectory sensitivity method so the complex nonlinear optimization control model is transformed into static linear integer programming model. In order to find the optimal solution, use heuristic algorithm and put forward Lsi index. With the numerical order, judge the degree of the improvement of the node load so as to determine location of cutting load and cutting load capacity. The results of simulation show that the method not only simplifies the calculation but also has no iteration.Then, this paper puts forward the dynamic reactive power capacity optimization model. From the Angle of the sensitive load, use the voltage sag index as voltage improvement goals. Based on the monte carlo theory, build the fault model and failure type model and generate a voltage sag probability table. Set up voltage sag cost model and establish the total annual cost optimization model considering the active loss and system cost of STATCOM. With the help of curve fitting method, calculate the relation between cost of voltage sag and capacity of STATCOM. So the optimization of capacity is simplified. The results of simulation show that the method is correct and effective.Finally, this paper puts forward the coordinated emergency voltage control strategy. Use the index of voltage sag probability as improved object. Consider the emergency load control and dynamic reactive power compensation of STATCOM at the same time. Use STATCOM as the first compensation, if it can not meet the requirements, consider emergency load control as the second compensation. Cooperate coordinately to minimize voltage sag occurrence probability. The results of simulation show that voltage sag probability is greatly reduced and the effect is obvious.