Research On Voltage Stability Of Power System

The tendency and the characteristic of the modern power system's development is extra-high voltage, great electric systems, transmission with long distance and heavy loads. And it makes the power system stability more striking, the regulation of the voltage more difficult. In the mean time, the increase of a large number of the air conditioner loads, modern electric and electronic equipments, widely used reactive power/voltage control devices on distribution systems bring badly influence to the system stability, though the supply of the electricity to the user improves. The research and experience inside and outside the country indicates that, to keep the voltage stability and power/angle stability is a very important technical question for discussion when running the modern power systems.In this thesis we summarized the definition of voltage stability, its phenomena and mechanism, and its classification and study methods. Then according to the actual state of the study in voltage stability index aspect, we proposed a new index which is quite easy to calculate and can be implemented for online use. The method does not need complicated matrix computations and other time-consuming calculations, so the solution can be expected to be obtained faster. Besides this method can identify the exact location of voltage collapse and quantify how close a particular operating point is to voltage collapse.Although power transmission paths are very complex in practical power systems, the voltage stability degree of power systems can be represented by the voltage stability of the power transmission path which is the most prone to voltage instability due to the local nature of voltage instability problems. Through the ordinary calculation of the power flow, and using the information of conductance matrix, the method can work out the weakest nodes of the system loads. Based on the definition of electrical distance, find the nodes in the generators (key generator nodes) which have close connection with the weakest load nodes. Then make equivalence to the path (power transmission path) between the weak load nodes and the key generator nodes. And the stability margin index can be found from the equivalent simple system.Through the analysis based on the IEEE 39-bus example, the method can easily find the weakest nodes of the system loads and calculate the voltage stability margin index quickly and exactly. Because the generators of Shandong Power System distribute at the west, and the loads distribute at the east part. Power must be transferred from west to east. And this could easily affect the power stability. The result of simulation of the practical Shandong power system indicates that the method can be used to on-line analysis of power system.