【作者】 常涛；

【导师】 孙才新；

【作者基本信息】 重庆大学 ， 电气工程， 2010， 博士

【摘要】 电气设备的安全运行是电力系统安全、稳定、经济运行的重要基础。随着特高压电网建设,电力输送容量更大,覆盖范围更广,全国各级电网联系也更加紧密,因此电网事故的危害性更大。大型电力变压器是电力系统的枢纽设备,实时检测变压器绝缘状态,准确预知故障,做到防患于未然,是保证电网安全运行、提高设备利用率和降低设备检修费用的重要举措,也是建设坚强智能电网的关键技术课题,意义十分重大。油中溶解气体分析是目前判断油浸式电力变压器早期潜伏性故障最方便、最有效的方法,实际应用最为广泛,已成为判断充油电气设备内部故障和监视设备安全运行不可缺少的手段。近年来,应用气体传感技术开发研制小型气体检测装置,已成为新的发展趋势,目的在于实现对变压器油中溶解气体进行在线监测,随时掌握设备的运行状况。近年来传感技术取得了突破性进展,特别是纳米技术的发展,为传感器研发提供了全新的材料和加工方法,其中碳纳米管气敏传感器已经成为新的研究热点。作者在现有变压器油中气体检测和分析方法研究基础上,对纳米气敏传感技术应用于油中气体检测和分析进行了深入研究,研制了新型碳纳米管气体传感器,对碳纳米管气敏机理和特性进行研究,并通过气敏试验和计算机仿真进行验证,掌握了基本规律,提出了一种基于动态隧道模糊C均值的油中溶解气体故障诊断算法,丰富了变压器故障特征分析手段。对碳纳米管的制备、化学修饰以及表征方法进行了探讨,首次提出通过对碳纳米管进行化学修饰,来实现对变压器油中溶解气体的检测。采用透射电子显微镜技术对碳纳米管进行了微观结构分析,表明化学修饰使碳纳米管长度变短,端口打开,比表面积增大,同时管壁被撕裂,缺陷变大增多;采用红外吸收光谱分析技术进行了碳纳米管活性官能团分析,发现碳纳米管端头、部分侧壁或有缺陷的位置接上了羟基、羧基、羰基等活性官能团,可以作为吸附油中溶解气体分子的中心。表明化学修饰可以提高碳纳米管对变压器油中溶解气体的敏感性。研制了一种碳纳米管薄膜传感器(MWNTs),构建了传感器检测油中溶解气体试验装置。在此基础上,对碳纳米管的温度特性进行了测试,分析了碳纳米管薄膜的导电模型,发现化学修饰改变了碳纳米管的电学特性,使其具有更好的半导体性质。首次进行了油中溶解气体碳纳米管的气敏检测,机理分析和实验结果表明,混酸修饰使碳纳米管产生了大量的活性官能团,为气体的吸附增加了更多的活性点,提高了传感器对油中溶解气体的敏感性;采用氯化镍掺杂加剧了碳纳米管的结构缺陷,改变了表面势垒,构造了局部催化活性中心,提高了电荷转移能力,进一步改善了碳纳米管的气敏性,检测灵敏度更高。首次对羟基化碳纳米管(SWNT-OH)对变压器油中各溶解气体的吸附特性进行了计算机仿真,基于第一性原理及密度泛函理论,采用Materials Studio进行了大量计算,结果表明SWNT-OH对有机气体的吸附能力大于无机气体,而且在有机气体中,对C2H2最为敏感。将实验结果与仿真结果进行了对比分析,得到了很好的验证。针对模糊C均值聚类算法(FCM)用于溶解气体分析时易陷入局部极小的问题,利用全局最优化性能强的动态隧道算法,将两种算法结合,提出一种基于动态隧道FCM聚类的变压器故障诊断算法。该算法首先采用FCM算法聚类得到局部最优值,再利用动态隧道算法以该局部最优值为初始值寻找更小的能量盆地,再将其值返回给FCM算法进行迭代寻优,直到找到全局最小值。通过该算法应用于变压器DGA数据分析,从而实现变压器的故障诊断。变压器油色谱样本及加噪样本故障诊断试验表明,该算法能快速、有效地对样本进行聚类,具有较高的诊断准确率。更多还原

【Abstract】 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.更多还原