Detection Of Dissolved Gas In Transformer Oil By Carbon Nanotubes And Dynamic Tunnel Fuzzy Fault Diagnosis

The safe operation of electrical equipment is the basic of the safety, stability and economical operation of electrical power system. Along with the extra-high voltage grid construction, power transmission capacity becomes larger, coverage area becomes wider, and the national power grids at all levels are closely linked to each other, so the harm of grid accidents would be more serious. Large power transformer, as the key equipment of power system, plays influential role to ensure the safe operation of power system. Real-time detecting the insulation state of transformer, accurately predicting the fault and avoiding possible trouble are important measures to ensure the safe operation of the electrical grid, to improve equipment utilization and reduce costs of equipment maintenance, which are also key technical issuese of constructing the strong and intelligent electrical grid.Dissolved gas-in-oil analysis (DGA) is the most convenient and effective method of judging the early potential fault of oil-immersed power transformers at present, and the method is the most extensive one in the real application, which has become an indispensable approach to judge the internal fault of oil-filled electrical equipment and oversee the safe operation of equipment. For the past few years, it has become the new trend to develop the pint-sized gas-detecting device by using the gas sensing technology, which is aimed at achieving on-line monitoring to dissolved gas in transformer oil and grasping the operational state of equipment at any time. In recent years a breakthrough has been making in the sensor technology. Especially the development of nanotechnology has been providing the new material and processing method, in which the CNTs gas sensor has become the new research focus.Based on the study of the existing method of detecting and analyzing dissolved gas-in-oil, the Nano-gas sensing technology, used in the detection and analysis of dissolved gas-in-oil, is studied in depth in this paper. A new kind of CNTs gas sensor is developed and the verification of experiments and theoretical simulation for gas-sensing properties are carried out. The basic laws are grasped, and a fault diagnosing method of dissolved gas-in-oil based on dynamic tunneling fuzzy C-means Algorithm(DTFCM)is proposed, which enriches analytical tools of transformer fault features.The preparation, modification and characterization are investigated. For the first time, it is introduced to modify CNTs to test the dissolved gas-in-oil of transformer.,. The micro-structure analysis of CNTs is carried out using transmission electron microscope, which shows that chemical modification reduces the length of MWNTs, opens the ports, enlarges the specific surface area. And the walls of tubes are torn, then larger defects are generated. The analysis of CNTs'active functional groups is carried out using infrared spectrum technology, which shows that the parts such as CNTs tips, some side walls or the positions of defectiveness, are connected with active functional groups such as hydroxide radical, carboxyl, carbonyl etc., and could be the centre of physical adsorbing dissolved gas-in-oil. It shows that chemical modification may improve the CNTs sensibility of dissolved gas-in-oil.The MWNTs film Sensor is developed, and the testing device for the sensor detecting gas-in-oil is built. The temperature property of MWNTs is tested, and the conduction model of the MWNTs film is analyzed, then it is found that chemical modification changes electrical characteristics of MWNTs, and makes CNTs have better semiconductor properties.For the first time, gas sensing detection of dissolved gas-in-oil is carried out using CNTs. The detection results and mechanism analysis show that the modification by mixed acid makes CNTs generate a number of active functional groups such as hydroxide radical, carboxyl, carbonyl and so on, which increases more active sites for gas absorption, and improve the sensibility of the sensor absorbing dissolved gas-in-oil; doping nickel chloride aggravates structure defects of CNTs, changes surface potential barrier, Constructs partial catalytic active centre, and enhances the ability of charge transfer, further improves the sensibility of CNTs.For the first time, the computer simulation of the absorbing ability of SWNT-OH to dissolved gas-in-oil is carried out. According to the first-principles and DFT(Density Functional Theory), the computer simulation is carried out by Materials Studio simulation software, then it is obtained that the absorbing ability of SWNT-OH to organic gas is better than that to inorganic gas, among which sensitivity to C2H2 is the best. The conclusion is well verified by contrastive analysis between experimental results and simulation results.Aiming at the problem that Fuzzy C-Means (FCM) clustering algorithm is likely to fall into local minimum point when being used for dissolved gas analysis, Dynamic tunneling (DT) algorithm was introduced for its high global optimization performance. Then a DT-FCM algorithm was presented based on these two algorithms. On the Basis of local minimum obtained by optimization searching of FCM algorithm, using dynamic tunneling process to search a lower energy valley, then the value was submitted to FCM algorithm for iterative optimization until global minimum point was found by repeating the process. Through the application of this algorithm for DGA in transformer oil, transformer fault diagnosis can be achieved. These tests for fault diagnosis of chromatography transformer oil and noise samples show that, the algorithm can cluster samples quickly and effectively and with high accuracy for diagnosis.