变压器油纸绝缘热老化的时频域介电和空间电荷特性研究
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摘要
变压器的严重事故不但会导致自身的损坏，还会中断电力供应，造成巨大的经济损失。由内绝缘老化而引发的变压器故障占变压器事故的重要部分。以介电响应为基础的极化/去极化电流法和频域介电谱法不仅是无损的电气诊断技术，而且是变压器绝缘状态诊断中本领域国内外学者研究的热点之一。研究一种对变压器绝缘老化进行无损诊断的介电响应测量新方法或新特征量是尚需解决的难题之一。变压器油纸绝缘的介电性能和空间电荷特性的联系、油纸绝缘介质在老化过程中绝缘油性能对空间电荷形成及迁移的影响、以及作为油纸绝缘老化产物且直接影响油纸绝缘介电性能的水分对多层油纸绝缘介质空间电荷的影响，均是需要研究解决的问题。另外，由于绝缘材料在交流下空间电荷测试的复杂性和硬件设备性能的限制，绝缘材料交流空间电荷特性的研究未得到广泛开展，油纸绝缘介质的交流空间电荷特性也是需要研究的课题。因此，本文变压器油纸绝缘热老化的时频介电和空间电荷特性的研究具有重要的理论价值和工程实际意义。
本文首先采用极化/去极化电流和频域介电谱测试技术研究不同老化状态变压器油纸绝缘试品的极化/去极化电流特性和频域介电谱特性，分别研究提取对油纸绝缘试品老化状态反应敏感的时域和频域介电特征量，建立时域和频域介电特征量与绝缘老化状态的量化关系，并研究温度对变压器油纸绝缘试品极化/去极化电流特性和频域介电特性的影响；然后采用电声脉冲法研究不同热老化程度绝缘油浸渍油纸绝缘试品和不同水分含量油浸绝缘纸在直流下的空间电荷特性，分别分析绝缘油热老化和水分对油纸绝缘介质电荷积聚行为的影响；最后采用改进的电声脉冲法测试系统研究不同热老化状态油纸绝缘介质在正弦交流下的空间电荷特性，分析油纸绝缘介质在正弦交流加压、瞬时去压和去压过程中空间电荷的动态行为。论文取得的主要创新性成果有：
(1)首次提出采用“稳定去极化电量”评估油纸绝缘老化状态的方法。通过不同老化状态变压器油纸绝缘试品的Debye电路参数计算得到的去极化电量对绝缘老化状态反应极为敏感，不同老化状态变压器油纸绝缘试品的“稳定去极化电量”随绝缘纸聚合度降低呈指数规律增大，利用“稳定去极化电量”可评估油纸绝缘老化状态。
(2)首次提出采用在低频段特征频率处的介电特征量评估油纸绝缘老化状态的方法。变压器油纸绝缘试品在低频段的频域介电特征量对其绝缘老化状态反应敏感，不同老化程度油纸绝缘试品在特征频率处（10-3Hz,10-2Hz和10-1Hz）的εr和tanδ值与绝缘纸聚合度满足指数函数关系，利用低频介电特征量可评估油纸绝缘老化状态。
(3)油纸绝缘试品在低频段特征频率处（10-3Hz,10-2Hz和10-1Hz）的εr和tanδ值随温度的升高呈指数规律增大，提出利用“频温平移”法可将不同测试温度下的频域介电特征量归算到参考温度，解决了温度对频域介电特征量的影响。研究得到“频温平移因子”随温度的升高呈指数规律增大。
(4)采用电声脉冲法分别研究了绝缘油热老化和水分对多层油纸绝缘介质直流空间电荷特性的影响。与油纸绝缘整体热老化的空间电荷特性相比，发现绝缘油性能和水分对多层油纸绝缘介质直流空间电荷的影响显著。绝缘油热老化越严重，相应绝缘油浸渍油纸绝缘试品内部越容易注入和积聚电荷；油浸绝缘纸试品内部的空间电荷总量、表面陷阱能级密度和电场畸变率均随绝缘油老化程度的加重而增大。油纸绝缘试品的水分含量越高，越利于电荷的注入和迁移，而且油纸绝缘试品内部慢速运动电荷的量也越少。
(5)采用改进的电声脉冲测试系统研究了油纸绝缘热老化对其工频电压下空间电荷特性的影响规律。与直流条件下相比，在工频电压下油纸绝缘介质内部积聚的电荷量显著减少；在工频场强下，相位相差180o的两相位下电极处的电荷极性相反，电荷密度值基本相同；工频加压过程中，90o和270o相位下绝缘纸-绝缘纸界面处积聚的电荷随着油纸绝缘热老化的进行会不断向对面电极迁移。
The serious accidents of transformer can not only cause their own damage, but alsointerrupt the power supply, causing huge economic losses. Transformer failures causedby internal insulation aging is an important part of the transformer accident. Thepolarization/depolarization current method and frequency domain dielectricspectroscopy based on dielectric response are not only non-destructive electricaldiagnostic technique, and also the research focus of domestic and foreign scholars in thefield of transformer insulating condition assessment. Investigating new method or newcharacteristics parameters for diagnosing the transformer insulation aging and assessingits life non-destructively using dielectric response technique is difficult question to bersolved. The relationship between dielectric properties of transformer oil-paperinsulation and its space charge characteristics, the influence of insulation oil property onthe formation and migration of space charge in the aging process of oil-paper insulation,both are need to be investigated. What’s more, moisture is not only the byproduct ofoil-paper insulation aging, and also can deteriorate the property of the oil-paperinsulation. The influence of moisture on the charge distribution of oil-paper insulation isalso need to be studied. In addition, the space charge characteristics of insulatingmaterials under AC condition have not been widely carried out due to the complexity ofthe testing and the hardware restriction. There are many transformers running under theAC condition. It is a new topic to explore the influence of aging on the AC space chargecharacteristics of oil-paper insulation.
In this paper, firstly, the polarization/depolarization current and frequency domaindielectric spectroscopy characteristics of transformer oil-paper insulation sample withdifferent aging degree was measured using the polarization/depolarization current andfrequency domain dielectric spectroscopy testing technology. The time domain andfrequency domain dielectric characteristic parameters which are sensitive to the agingstate of oil-paper insulation sample were investigated. The quantitative relationshipbetween time domain or frequency domain dielectric characteristic parameters and theinsulation aging status was established. The temperature effect on thepolarization/depolarization current and frequency domain dielectric characteristics oftransformer oil-paper insulation was also investigated. Secondly, the DC space charge
Supported by: The National Basic Research Program of China (973Program)(2009CB724505-1). characteristics of oil-paper insulation samples impregnated with oil aged for differenttimes and oil-paper insulation samples with different moisture content were measuredby pulse electro-acoustic (PEA) method. The influence of oil aging and moisture on thespace charge dynamic behavior of oil-paper insulation was analyzed respectively. Lastly,space charge characteristics of oil paper insulation with different aging state under thesinusoidal (50Hz) AC were studied using the improved pulse electro-acoustic method.The dynamic behavior of space charge for oil-paper insulation under sinusoidal ACcondition was analyzed. The main innovative achievements of this paper are asfollowing:
(1) The depolarization charge quantity of oil-paper insulation samples calculatedusing their Debye circuit parameters is very sensitive to their aging condition. There isan exponential relation between the “stable depolarization charge quantity” of oil-paperinsulation sample and the degree of polymerization (DP) of paper. The “stabledepolarization charge quantity” can be used to predict the aging condition of oil-paperinsulation.
(2) The frequency domain dielectric characteristics parameters of the transformeroil-paper insulation in the low frequency band are sensitive to the insulation aging state.The ε 'rand tanδ values at10-3Hz,10-2Hz and10-1Hz of aged oil impregnatedpressboards have an exponential function with the DP. The frequency domain dielectriccharacteristic quantity (ε 'rand tanδ) of the oil-paper insulation sample in10-3-10-1Hzcan reflect the aging status of oil impregnated insulation paper.
(3) The ε 'rand tanδ values at10-3Hz,10-2Hz and10-1Hz of aged oil impregnatedpressboards increase in an exponential way with tepmperature. The“frequency-temperature shift” method could be used to impute the frequency domaindielectric characteristics parameters at different test temperatures to the referencetemperature. In this way, the temperature effect on the frequency domain dielectriccharacteristics parameters can be resolved. In addition, the “frequency-temperature shiftfactor” increases exponentially with temperature.
(4) The effect of thermally aged oil and moisture on DC space charge dynamics inoil-paper insulation system had been investigated using the PEA technique respectively.Compared with the space charge dynamics result of oil-paper insulation thermal aging,it is founded that the influence of insulating oil properties and moisture on the DC spacecharge of multi-layer oil-paper insulation is significant. The total amount of charge, thesurface trap energy density and the electric field distortion of the oil-paper sample increase with the oil aging degree. The higher moisture content of the oil-paper sampleis helpful to the charge injection and migration. The higher mobility of the trappedcharges leads to less slow moving charges trapped in the sample with higher moisturecontent.
(5) Space charge characteristics of oil-paper insulation with different aging stateunder the sinusoidal AC were studied using the improved PEA system. The amount ofspace charge accumulated in the oil-paper insulation sample under sinusoidal ACcondition is significantly reduced compared with that under DC condition. The chargepolarity is opposite at the electrode position for two phases where the phase differencebetween them is180o. In the process of AC electric field applied, the space chargeaccumulated at the paper-paper interface under the phase90oand270omigrates to theopposite electrode with the aging conducted.
本文首先采用极化/去极化电流和频域介电谱测试技术研究不同老化状态变压器油纸绝缘试品的极化/去极化电流特性和频域介电谱特性，分别研究提取对油纸绝缘试品老化状态反应敏感的时域和频域介电特征量，建立时域和频域介电特征量与绝缘老化状态的量化关系，并研究温度对变压器油纸绝缘试品极化/去极化电流特性和频域介电特性的影响；然后采用电声脉冲法研究不同热老化程度绝缘油浸渍油纸绝缘试品和不同水分含量油浸绝缘纸在直流下的空间电荷特性，分别分析绝缘油热老化和水分对油纸绝缘介质电荷积聚行为的影响；最后采用改进的电声脉冲法测试系统研究不同热老化状态油纸绝缘介质在正弦交流下的空间电荷特性，分析油纸绝缘介质在正弦交流加压、瞬时去压和去压过程中空间电荷的动态行为。论文取得的主要创新性成果有：
(1)首次提出采用“稳定去极化电量”评估油纸绝缘老化状态的方法。通过不同老化状态变压器油纸绝缘试品的Debye电路参数计算得到的去极化电量对绝缘老化状态反应极为敏感，不同老化状态变压器油纸绝缘试品的“稳定去极化电量”随绝缘纸聚合度降低呈指数规律增大，利用“稳定去极化电量”可评估油纸绝缘老化状态。
(2)首次提出采用在低频段特征频率处的介电特征量评估油纸绝缘老化状态的方法。变压器油纸绝缘试品在低频段的频域介电特征量对其绝缘老化状态反应敏感，不同老化程度油纸绝缘试品在特征频率处（10-3Hz,10-2Hz和10-1Hz）的εr和tanδ值与绝缘纸聚合度满足指数函数关系，利用低频介电特征量可评估油纸绝缘老化状态。
(3)油纸绝缘试品在低频段特征频率处（10-3Hz,10-2Hz和10-1Hz）的εr和tanδ值随温度的升高呈指数规律增大，提出利用“频温平移”法可将不同测试温度下的频域介电特征量归算到参考温度，解决了温度对频域介电特征量的影响。研究得到“频温平移因子”随温度的升高呈指数规律增大。
(4)采用电声脉冲法分别研究了绝缘油热老化和水分对多层油纸绝缘介质直流空间电荷特性的影响。与油纸绝缘整体热老化的空间电荷特性相比，发现绝缘油性能和水分对多层油纸绝缘介质直流空间电荷的影响显著。绝缘油热老化越严重，相应绝缘油浸渍油纸绝缘试品内部越容易注入和积聚电荷；油浸绝缘纸试品内部的空间电荷总量、表面陷阱能级密度和电场畸变率均随绝缘油老化程度的加重而增大。油纸绝缘试品的水分含量越高，越利于电荷的注入和迁移，而且油纸绝缘试品内部慢速运动电荷的量也越少。
(5)采用改进的电声脉冲测试系统研究了油纸绝缘热老化对其工频电压下空间电荷特性的影响规律。与直流条件下相比，在工频电压下油纸绝缘介质内部积聚的电荷量显著减少；在工频场强下，相位相差180o的两相位下电极处的电荷极性相反，电荷密度值基本相同；工频加压过程中，90o和270o相位下绝缘纸-绝缘纸界面处积聚的电荷随着油纸绝缘热老化的进行会不断向对面电极迁移。
The serious accidents of transformer can not only cause their own damage, but alsointerrupt the power supply, causing huge economic losses. Transformer failures causedby internal insulation aging is an important part of the transformer accident. Thepolarization/depolarization current method and frequency domain dielectricspectroscopy based on dielectric response are not only non-destructive electricaldiagnostic technique, and also the research focus of domestic and foreign scholars in thefield of transformer insulating condition assessment. Investigating new method or newcharacteristics parameters for diagnosing the transformer insulation aging and assessingits life non-destructively using dielectric response technique is difficult question to bersolved. The relationship between dielectric properties of transformer oil-paperinsulation and its space charge characteristics, the influence of insulation oil property onthe formation and migration of space charge in the aging process of oil-paper insulation,both are need to be investigated. What’s more, moisture is not only the byproduct ofoil-paper insulation aging, and also can deteriorate the property of the oil-paperinsulation. The influence of moisture on the charge distribution of oil-paper insulation isalso need to be studied. In addition, the space charge characteristics of insulatingmaterials under AC condition have not been widely carried out due to the complexity ofthe testing and the hardware restriction. There are many transformers running under theAC condition. It is a new topic to explore the influence of aging on the AC space chargecharacteristics of oil-paper insulation.
In this paper, firstly, the polarization/depolarization current and frequency domaindielectric spectroscopy characteristics of transformer oil-paper insulation sample withdifferent aging degree was measured using the polarization/depolarization current andfrequency domain dielectric spectroscopy testing technology. The time domain andfrequency domain dielectric characteristic parameters which are sensitive to the agingstate of oil-paper insulation sample were investigated. The quantitative relationshipbetween time domain or frequency domain dielectric characteristic parameters and theinsulation aging status was established. The temperature effect on thepolarization/depolarization current and frequency domain dielectric characteristics oftransformer oil-paper insulation was also investigated. Secondly, the DC space charge
Supported by: The National Basic Research Program of China (973Program)(2009CB724505-1). characteristics of oil-paper insulation samples impregnated with oil aged for differenttimes and oil-paper insulation samples with different moisture content were measuredby pulse electro-acoustic (PEA) method. The influence of oil aging and moisture on thespace charge dynamic behavior of oil-paper insulation was analyzed respectively. Lastly,space charge characteristics of oil paper insulation with different aging state under thesinusoidal (50Hz) AC were studied using the improved pulse electro-acoustic method.The dynamic behavior of space charge for oil-paper insulation under sinusoidal ACcondition was analyzed. The main innovative achievements of this paper are asfollowing:
(1) The depolarization charge quantity of oil-paper insulation samples calculatedusing their Debye circuit parameters is very sensitive to their aging condition. There isan exponential relation between the “stable depolarization charge quantity” of oil-paperinsulation sample and the degree of polymerization (DP) of paper. The “stabledepolarization charge quantity” can be used to predict the aging condition of oil-paperinsulation.
(2) The frequency domain dielectric characteristics parameters of the transformeroil-paper insulation in the low frequency band are sensitive to the insulation aging state.The ε 'rand tanδ values at10-3Hz,10-2Hz and10-1Hz of aged oil impregnatedpressboards have an exponential function with the DP. The frequency domain dielectriccharacteristic quantity (ε 'rand tanδ) of the oil-paper insulation sample in10-3-10-1Hzcan reflect the aging status of oil impregnated insulation paper.
(3) The ε 'rand tanδ values at10-3Hz,10-2Hz and10-1Hz of aged oil impregnatedpressboards increase in an exponential way with tepmperature. The“frequency-temperature shift” method could be used to impute the frequency domaindielectric characteristics parameters at different test temperatures to the referencetemperature. In this way, the temperature effect on the frequency domain dielectriccharacteristics parameters can be resolved. In addition, the “frequency-temperature shiftfactor” increases exponentially with temperature.
(4) The effect of thermally aged oil and moisture on DC space charge dynamics inoil-paper insulation system had been investigated using the PEA technique respectively.Compared with the space charge dynamics result of oil-paper insulation thermal aging,it is founded that the influence of insulating oil properties and moisture on the DC spacecharge of multi-layer oil-paper insulation is significant. The total amount of charge, thesurface trap energy density and the electric field distortion of the oil-paper sample increase with the oil aging degree. The higher moisture content of the oil-paper sampleis helpful to the charge injection and migration. The higher mobility of the trappedcharges leads to less slow moving charges trapped in the sample with higher moisturecontent.
(5) Space charge characteristics of oil-paper insulation with different aging stateunder the sinusoidal AC were studied using the improved PEA system. The amount ofspace charge accumulated in the oil-paper insulation sample under sinusoidal ACcondition is significantly reduced compared with that under DC condition. The chargepolarity is opposite at the electrode position for two phases where the phase differencebetween them is180o. In the process of AC electric field applied, the space chargeaccumulated at the paper-paper interface under the phase90oand270omigrates to theopposite electrode with the aging conducted.
引文
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