基于介电响应法的发电机主绝缘状态评估技术研究

发布时间：2018-04-27 14:25

本文选题：发电机 + 环氧-云母绝缘　；参考：《西南交通大学》2017年硕士论文

【摘要】：大型汽轮发电机是发电系统的核心设备,其主绝缘主要由环氧云母复合电介质组成,主绝缘的老化状态将严重影响发电机的使用寿命。本文基于频域介电谱法(Frequency Domain Spectroscopy,FDS)对发电机主绝缘的老化状态评估展开研究,采用理论分析、物理模型构建、试验验证的方法,研究了主绝缘的老化特性和介电响应特性,对于利用介电响应法实现发电机主绝缘老化状态评估具有重要指导意义。搭建了发电机定子主绝缘试样电—热—机械多应力联合老化试验平台和FDS测试平台,对不同老化程度的试样分别开展了 FDS、吸收比、介质损耗等测试,此外通过试验研究了温度对频域介电谱的影响,运用电介质极化理论分析了试样频域介电谱变化机理,采用带直流电导修正的双弛豫Cole-Cole模型对FDS测试值进行拟合,研究了老化和温度对弛豫模型参数的影响。试验结果表明:吸收比和介损的变化规律反映出线棒绝缘随加速老化的进行而逐渐劣化,验证了老化试验平台的有效性;双弛豫Cole-Cole模型可有效拟合测试值;随着老化时间的增加,试样的复介电常数实部和虚部均逐渐增大,在较低频段(10-3～100Hz)增大趋势更为明显,直流电导率和界面极化弛豫强度迅速增大,弛豫时间呈减小趋势,分布参数没有明显的变化规律,其值分布于0.7～0.9之间;前两个周期与后三个周期的转向极化弛豫的弛豫参数差异较大,认为线棒绝缘老化严重时,绝缘的弛豫机制发生改变,产生了一个新的弛豫过程;对不同老化程度的试样,FDS测试结果和弛豫模型参数具有较高的敏感性并随老化呈现一定规律性,因此可将FDS法用于主绝缘的老化评估。研究了温度对主绝缘FDS特性的影响。随着温度升高,复介电常数实部和虚部的频谱曲线向高频方向移动;温度升高加强了界面极化强度和偶极子转向极化强度,在虚部频谱内,界面极化弛豫起主导作用的频率范围变宽;不同温度下的界面极化弛豫时间常数满足Arrhenius方程,根据过渡态理论,计算得到界面极化弛豫对应的活化焓为103.1kJ/mol;活化熵随温度升高而增大,表明绝缘体系有序性减小;活化能减小,表明各种极化过程更易完成,因此可用过渡态理论解释发电机主绝缘频域介电谱的温度依存性。最后通过构造温度主曲线不仅能消除温度对介电谱的影响,还能拓展测试频率范围。最后对珠海发电厂02#机组开展了现场FDS测试,结果表明:现场试验测试结果与实验室研究结论基本一致,可将频域介电谱法初步推广应用于发电机主绝缘老化状态的现场评估。
[Abstract]:Large turbogenerator is the core equipment of power generation system, its main insulation is mainly composed of epoxy mica composite dielectric, the aging state of main insulation will seriously affect the service life of generator. In this paper, based on frequency Domain spectroscopy-FDS in frequency domain, the aging characteristics and dielectric response of main insulation of generator are studied by means of theoretical analysis, physical model construction and experimental verification. It is of great significance to evaluate the aging state of main insulation of generator by using dielectric response method. An electric-thermal-mechanical multi-stress combined aging test platform and a FDS test platform were set up for the main insulation samples of the generator stator. The FDS, absorption ratio and dielectric loss of the samples with different aging degrees were tested, respectively. In addition, the influence of temperature on the dielectric spectrum in frequency domain is studied experimentally. The dielectric spectrum variation mechanism in frequency domain is analyzed by using dielectric polarization theory. The double relaxation Cole-Cole model with modified DC conductance is used to fit the measured values of FDS. The effects of aging and temperature on the parameters of relaxation model were studied. The experimental results show that the variation of absorption ratio and dielectric loss reflects the deterioration of the insulation of the wire rod with the accelerated aging, which verifies the validity of the aging test platform, and the double relaxation Cole-Cole model can fit the measured values effectively. With the increase of aging time, the real and imaginary parts of the complex dielectric constant of the sample increase gradually, and the increasing trend is more obvious in the lower frequency band, the DC conductivity and the interfacial polarization relaxation strength increase rapidly, and the relaxation time decreases. The relaxation parameters of the first two cycles and the last three periods are different greatly. It is considered that the relaxation mechanism of the insulation changes with the aging of the wire rod insulation. There is a new relaxation process which is sensitive to the test results and relaxation model parameters of samples with different aging degrees and has a certain regularity with aging. Therefore FDS method can be used to evaluate the aging of main insulation. The effect of temperature on the characteristics of main insulation FDS is studied. With the increase of temperature, the spectrum curves of real and imaginary parts of complex permittivity move to high frequency, and the interfacial polarization intensity and dipole turning polarization intensity are enhanced with the increase of temperature, which is in the imaginary region spectrum. The frequency range of the interfacial polarization relaxation is widened, and the interfacial polarization relaxation time constant at different temperatures satisfies the Arrhenius equation, according to the transition state theory, The activation enthalpy corresponding to the interfacial polarization relaxation is 103.1 kJ / mol. The activation entropy increases with the increase of temperature, indicating that the order of the insulation system decreases, and the activation energy decreases, indicating that the various polarization processes are easier to complete. Therefore, the transition state theory can be used to explain the temperature dependence of the dielectric spectrum in the frequency domain of the main insulation of the generator. Finally, the influence of temperature on dielectric spectrum can be eliminated and the range of test frequency can be expanded by constructing the main temperature curve. Finally, the field FDS test was carried out for the units of Zhuhai Power Plant 02#. The results show that the field test results are in good agreement with the results of the laboratory study, and the frequency domain dielectric spectrum method can be applied to the field evaluation of the main insulation aging state of the generator.
【学位授予单位】：西南交通大学
【学位级别】：硕士
【学位授予年份】：2017
【分类号】：TM31

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