Voltage Sag Assessment Study

As the updating of the electric equipment, digital automate control device are used widely in industry since 1980s. But these ones have a deficiency: they are easily disturbed by the voltage. So people put forward higher request towards the quality of the power system. And during the different reasons which affect the power quality , the Voltage collapse stands more than 80 percent of the whole Complaints of the consumer. So the Voltage collapse becomes the most serious problem among the power quality problems and the new challenge produced by the more advanced society.This thesis first introduces the basic concept of the Voltage collapse, including the definition, the causes, and three characters figuring the degree of Voltage collapse. Then analyses the range of Voltage collapse , and the two methods for analyzing which are the way of critical distance and fault points. Afterward the article focus on the two evaluating means: the way based on the real-data from locale and the way of digital simulation and theoretics analysis.(1) In the method based on the real-data, the article builds the Voltage collapse measuring system using LabVIEW, which is the famous virtual instrument software. The real-time display of the characters of Voltage collapse is realized by the data simulated through the MATLAB. Thesis also compares several methods for scaling characters of Voltage collapse.(2) In the digital simulation, thesis builds a basic math model which include the type ,the transmission line , the position and the persisting time of a fault, and simulates 500 times in a Standard IEEE 3 Generators and 9 buses using MATLAB with this model. From the result the most serious node can be seen through the amplitude andpersisiting time of Voltage collapse. The possible problem of the second Voltage collapse after the reclosing is analyzed in thesis. From the typical fault it can be concluded that the Voltage collapse of this situation is just a transition process, not a real Voltage collapse. The article also simulates the Busbar Breakdown separately. With the same condition in all the buses, the strongest bus can be found through the amplitude of Voltage collapse. What's more, thesis adds a new factor in to the probability evaluation which is the transition resistance. They are distributing stand by the normal school. Comparing the new result of simulation with the former one, it can be seen that the new one is more precise, and more close to the reality.