【作者】 马月姣；

【导师】 刘念；

【作者基本信息】 四川大学 ， 电机与电器， 2004， 硕士

【摘要】 大型发电机是大型电站的主要设备，是电力系统的心脏。现代社会日益剧增的电能需求和电力工业的迅速发展，对大型发电机的安全运行提出了更高的要求。大型发电机前端虽然有避雷器的保护，但雷电过电压对发电机所造成的损伤仍然不容忽视，特别是超高压输电线路上的雷电过电压对发电机绕组造成的冲击问题，最终可能导致严重的绝缘事故。同时，大型发电机的绝缘若受到损坏，需更换或修复的时间往往很长，这将造成很大的影响。因此，针对雷电过电压对大型发电机的冲击问题，重点开展大型发电机绕组电压在线分析计算的研究，对电力系统的安全运行具有重要的现实意义。 本文在分析和总结国内外旋转电机的雷电过电压分析方法及其研究现状的基础上，对发电机雷电过电压进行了理论分析，研究了大型发电机雷电过电压的在线监测方法，提出了用快速傅立叶变换FFT与多导体传输线理论相结合，计算大型发电机绕组电压分布的方法。 针对该研究课题，本文的主要研究内容如下： 1、对雷电过电压进行了详细的理论分析和计算。阐述了雷电过电压的产生、形成及雷电参数的计算；分别对输电线路、变电站和发电厂的雷电过电压进行了讨论，针对可能造成发电机雷害的过电压进行了分析计算，并根据具体情况对发电机绝缘损伤进行了分析。 2、研究了一种发电机雷电过电压的在线测量方法，此方法选用了LiNbO₃无源光纤电压传感器作为测量的传感元件，具有暂态性能好、响应速度快、不受外界电磁场干扰、频带宽、结构简单、造价低、绝缘性能优良、有电隔离的作用等优点。用这种方法可以准确的取得ns级的雷电过电压信号，确保了用计算机模型计算绕组电压分布的准确性。 3、建立了发电机绕组的多导体传输线模型，对发电机进行了线圈分析，给出了发电机单线圈、单相绕组、三相绕组以及大型发电机的多导体传输线模型。提出采用按时间抽取的快速傅立叶变换处理复杂激励源的方法，将在发电机出线端测得的雷电过电压信号分解为若干谐波信号，分别作为上述多导体传输线模型的激励源来计算发电机绕组匝电压，再通过时域上的叠加，得到发电机定子绕组实际的匝电压。 4、用MATLAB仿真软件对雷电冲击全波、波尾截断雷电冲击波和波前截断雷电冲击波进行了仿真，用快速傅立叶变换FFT将其分解为多次谐波，并采用幅值阀值法提取出幅值较大的谐波。以540槽三峡发电机为例，运用多导体传输线模型计算出其定子绕组的雷电冲击全波过电压，给出了仿真结果，验证了这个理论的正确性、可行性和优越性。 本文提出的大型发电机雷电过电压在线监测分析方法，采用实时性较好的信号测量方法，将多导体传输线理论与快速傅立叶变换相结合进行信号处理和计算，具有一定的现实意义。 关键词:大型发电机雷电过电压实时监测快速傅立叶变换多导体传输线理论绕组绝缘更多还原

【Abstract】 Large generator unit is the major equipment in larger power station, and also the heart of power system. The growing demand of electrical energy in modern society and the rapid development of power industry have resulted in a higher requisition for the safe generating operation of generator units. In the front of generators have some protective arrester, but the damage of generators made by lightning can’t be ignored. Particularly, the problem about lightning surge of large generator in high voltage power line, which may lead to serious insulative accident finally. Simultaneously, if generator’s insulation is damaged, it will cost very long time to repair or replace, which will bring about great influence. Therefore, the study of real-time analyzing for large generators under lightning overvoltage has very important practical meanings to safe generating operation of power systems.Based on the investigation of analysis methods for electric machines lightning overvoltage and its research status at home and abroad, this paper has made theoretical analysis on lightning overvoltage, researched an lightning overvoltage on-line monitoring method of large generator and presented the method which combines Fast Fourier Transformation (FFT) with multiconductor transmission line model to calculate voltage distribution in stator windings of large generator. For this subject, the main contents are described as follows: 1 Make the theoretical analysis and calculation on lightning overvoltage. Expound the generation, formation and parameters of lightning overvoltage.Respectively discuss lightning overvoltage of transmission line, electric substation and power station. Calculate lightning overvoltage of generator and the analyze insulation fault.2 Research a real-time lightning overvoltage monitoring method of generator, which used LiNbO3 as sensing element, thus it has many advantages, such as nice transient function, rapid respond, wide frequency, simple structure,good insulation, electric isolation, no electromagnetic field interference, and so on. This method can accurately get lightning overvoltage signal in ns grade, which ensures the accuracy of using computer model to calculate voltage distribution in windings.3 Build the model of multiconductor transmission line of generator windings and analyze generator windings. Give the generator single coih single phases three phase winding models and multiconductor transmission line model. Propose the method that DIT to deal with complex excitation. Then decompose lightning overvoltage signal to a number of harmonic waves and put these harmonic waves into the multiconductor transmission line model respectively to calculate voltages in the windings and then added these response of the harmonic waves in time domain, the real voltages of stator winding is obtained.4 Use MATLAB software to simulate all lightning wave lightning wave cut off in tail and lightning wave cut off in the head. Firstly, FFT decompose these waves into multiple harmonic waves; then according to the amplitude to take out of larger harmonic wave. For the generator with 540 slots of the Yangtze Gorges example, use the multiconductor transmission line model to calculate all wave lightning overvoltage in the stator windings and give the simulation result, which verified the accuracy, feasibility and advantage of this theory.This paper proposed the method of lightning overvoltage real-time monitoring of generators, which has combined the multiconductor transmission line theory and FFT. It has certain meanings in practices.更多还原