Research On The Phenomenon Of ’Virtual-short And Virtual-cut Off’ And Static Voltage Stability In Power System

The strength of the power structure is an important factor affecting the static voltagestability of power system, recently, research on the static voltage stability problem hasachieved many appreciable results, but present article is less considering the static voltagestability factor of grid structure. The thesis puts the power system structure as thebreakthrough point, and launches the research from the power system structure change trendand static voltage stability problems. Specific works are as follows:On the basis of in-depth research on the mechanism of voltage collapse, it finds thephenomenon that Some power system is approximately equal to the voltage across the line andthe branch is approximately zero transmission power when voltage is on the critical state. Atthis time, the corresponding structure of power system has changed, therefore, this thesisintroduces the concept of "Virtual-short, Virtual-cut off", and the phenomenon is called"Virtual-short, Virtual-cut off" of power system.When voltage change from a state of normal to a state of collapse, it qualitativelyanalyzes the real reason for the phenomenon of "Virtual-short, Virtual-cut off" to powersystem with the load of weak nodes load increases. It gives the characteristic structure of thesystem changes, and the power system is divided into the basic system, weak system andderivative system which research on strength change trend of grid structural.The mathematical model of grid power system in consideration of change of networkstructure and the current injection model is built based on the situation changes in gridstructure with load increasing so that the variation of grid network is found. On this basis, firstof all, redistribution of the system load caused by injection of power changes is derived in theprocess from the basic system to derivative system with "Virtual-short, Virtual-cut off", whichuse interpolation method. Secondly, it gives the variation of the admittance power system bythe redistribution of power system applied to admittance matrix of reflect the system structure,then, variation is given the power system with load growth.The variation of the system structure considering the static voltage stability criterion isgiven, by using eigenvalue analysis in process of load growth applied to the study of staticvoltage stability problems. For IEEE-30bus bar system and6bus bar system, it is simulated.The results show the practicality and effectiveness of the method to determine voltagestability, and the results show that considering the system structure factor is a new method andnew idea to be arrived, which is to analyze voltage stability at the same time.