Comprehensive evaluation of the transformer oil-paper insulation state based on RF-combination weighting and an improved TOPSIS method

The accurate identification of the oil-paper insulation state of a transformer is crucial for most maintenance strategies.This paper presents a multi-feature comprehensive evaluation model based on combination weighting and an improved technique for order of preference by similarity to ideal solution(TOPSIS)method to perform an objective and scientific evaluation of the transformer oil-paper insulation state.Firstly,multiple aging features are extracted from the recovery voltage polarization spectrum and the extended Debye equivalent circuit owing to the limitations of using a single feature for evaluation.A standard evaluation index system is then established by using the collected time-domain dielectric spectrum data.Secondly,this study implements the per-unit value concept to integrate the dimension of the index matrix and calculates the objective weight by using the random forest algorithm.Furthermore,it combines the weighting model to overcome the drawbacks of the single weighting method by using the indicators and considering the subjective experience of experts and the random forest algorithm.Lastly,the enhanced TOPSIS approach is used to determine the insulation quality of an oil-paper transformer.A verification example demonstrates that the evaluation model developed in this study can efficiently and accurately diagnose the insulation status of transformers.Essentially,this study presents a novel approach for the assessment of transformer oil-paper insulation.

Chaotic Characteristic of Time Series of Partial Discharge in Oil-Paper Insulation

The chaotic characteristics of time series of five partial discharge （PD） patterns in oil-paper insulation are studied. The results verify obvious chaotic characteristic of the time series of discharge signals and the fact that PD is a chaotic process. These time series have distinctive features, and the chaotic attractors obtained from time series differed greatly from each other by shapes in the phase space, so they could be used to qualitatively identify the PD patterns. The phase space parameters are selected, then the chaotic characteristic quantities can be extracted. These quantities could quantificationally characterize the PD patterns. The effects on pattern recognition of PRPD and CAPD are compared by using the neural network of radial basis function. The results show that both of the two recognition methods work well and have their respective advantages. Then, both the statistical operators under PRPD mode and the chaotic characteristic quantities under CAPD mode are selected comprehensively as the input vectors of neural network, and the PD pattern recognition accuracy is thereby greatly improved.

The Research of Connection between Degree of Polymerization and Frequency Domain Dielectric Spectroscopy Characteristics during Oil-Paper Insulation Aging

In order to study the linkage effects between degree of polymerization and frequency domain dielectric spectroscopy characteristics of oil-paper insulation, the frequency domain dielectric response test platform of oil-paper insulation is set up. Complex permittivity of oil-paper insulation respectively composed by new or aged oil and insulation paper with different DP are tested, and complex permittivity of oil-paper insulation respectively composed by insulation respectively composed by new oil and insulation paper with different DP and low or high moisture content are tested. The test results are analyzed, and the analysis results show that the degree of polymerization of insulation paper has an influence on complex permittivity of oil-paper insulation though influencing the distribution of moisture and acids between oil and paper.

A New Method for the Aging Evaluation of Oil-Paper Insulation Using η-Butanol and Methanol

To improve the accuracy and efficiency of the aging life prediction and assessment of transformer oil-paper insulation,and to make up for the deficiencies of traditional characterizers,such as 2-furfural,carbon monoxide,and carbon dioxide,a method for the simultaneous determination of methanol,ethanol,n−propanol,and η-butanol in oil with a single injection is established by headspace-gas chromatography-mass spectrometry.The measured results show that the determination limits of the four alcohol characterizers can be controlled to 10μg/kg level.Based on this method,the change patterns of the above four alcohols with thermal aging time and degree of polymerization are obtained through thermal aging experimental research.Ethanol,η-propanol,and η-butanol in oil indicate nearly linear correlations with thermal aging time and degree of polymerization,similar to that of methanol.By analyzing 52 sets of measured data of 500 kV EHV transformers in operation,η-butanol is found to have excellent performance,and a new method to evaluate the aging state of oil-paper insulation employing η-butanol and methanol is proposed along with the aging attention value model.The measured data of 500 kV EHV transformers in operation indicate that the combination of η-butanol and methanol as the preferred characterizers can effectively compensate for the shortcoming of traditional characterizers in the early stages of aging,and the feasibility of the method is verified.Two possible pathways for the generation of η-butanol by cellulose cleavage during the aging of oil-paper are proposed from the chemical structure of cellulose.

Study of predicting breakdown voltage of stator insulation in generator based on BP neural network

The breakdown voltage plays an important role in evaluating residual life of stator insulation in generator.In this paper,we discussed BP neural network that was used to predict the breakdown voltage of stator insulation in generator of 300MW/18kV.At first the neural network has been trained by the samples that include the varieties of dielectric loss factor tanδ,the partial discharge parameters and breakdown voltage.Then we tried to predict the breakdown voltage of samples and stator insulations subjected to multi-stress aging by the trained neural network.We found that it's feasible and accurate to predict the voltage.This method can be applied to predict breakdown voltage of other generators which have the same insulation structure and material.

Integrated Experimental and Simulation Investigation of Breakdown Voltage Characteristics Across Electrode Configurations in SF_(6) Circuit Breakers

This study investigates the breakdown voltage characteristics in sulfur hexafluoride(SF6)circuit breakers,employing a novel approach that integrates both experimental investigations and finite element simulations.Utilizing a sphere-sphere electrode configuration,we meticulously measured the relationship between breakdown voltage and electrode gap distances ranging from 1 cm to 4.5 cm.Subsequent simulations,conducted using COMSOL Multiphysics,mirrored the experimental setup to validate the model’s accuracy through a comparison of the breakdown voltage-electrode gap distance curves.The simulation results not only aligned closely with the experimental data but also allowed the extraction of detailed electric field strength,electric potential contours,and electric current flow curves at the breakdown voltage for gap distances extending from 1 to 4.5 cm.Extending the analysis,the study explored the electric field and potential distribution at a constant voltage of 72.5 kV for gap distances between 1 to 10 cm,identifying the maximum electric field strength.A comprehensive comparison of five different electrode configurations(sphere-sphere,sphere-rod,sphere-plane,rod-plane,rod-rod)at 72.5 kV and a gap distance of 1.84 cm underscored the significant influence of electrode geometry on the breakdown process.Moreover,the research contrasts the breakdown voltage in SF6 with that in air,emphasizing SF6’s superior insulating properties.This investigation not only elucidates the intricate dynamics of electrical breakdown in SF6 circuit breakers but also contributes valuable insights into the optimal electrode configurations and the potential for alternative insulating gases,steering future advancements in high-voltage circuit breaker technology.

Analysis of the breakdown mechanism for an ultra high voltage high-side thin layer silicon-on-insulator p-channel low-density metal-oxide semiconductor

This paper discusses the breakdown mechanism and proposes a new simulation and test method of breakdown voltage （BV） for an ultra-high-voltage （UHV） high-side thin layer silicon-on-insulator （SOI） p-channel low-density metal- oxide semiconductor （LDMOS）. Compared with the conventional simulation method, the new one is more accordant with the actual conditions of a device that can be used in the high voltage circuit. The BV of the SOI p-channel LDMOS can be properly represented and the effect of reduced bulk field can be revealed by employing the new simulation method. Simulation results show that the off-state （on-state） BV of the SOI p-channel LDMOS can reach 741 （620） V in the 3μm-thick buried oxide layer, 50μm-length drift region, and at -400 V back-gate voltage, enabling the device to be used in a 400 V UHV integrated circuit.

Comparative Evaluation of the Thermal Aging of Solid Insulation in Mineral Oil and Methyl Ester of Palm Kernel Oil

The purpose of this work is to determine the impact of thermal aging on the dielectric and physicochemical properties of the oil/paper mixed insulation. We performed a comparative analysis of dielectric paper dipped in two cooling fluids: palm kernel oil methyl ester (MEPKO) and mineral oil (MO). Two types of dielectric paper were used: Thermally Upgraded Kraft paper (TUK) and Nomex-910 paper (NP-910). An accelerated aging test was realized at 110°C during a total of 96 hours. Samples of oil and paper were collected after 0, 48, 72 and 96 hours for analyses purposes. The analyses performed included the measurement of the Breakdown voltage (BDV) of the dielectric papers, the Total Acid Number (TAN) and the Decay Dissolved Products (DDP) of the liquid dielectrics. The BDV of NP-910 is greater than the BDV of TUK. Concerning the type of oil, the BDV of dielectric papers impregnated with MEPKO is greater than the BDV of similar papers impregnated with MO, indicating a better preservation of paper when dipped in methyl esters. The analyses of TAN and DDP revealed that Nomex-910 improves the oxidation stability of MO, but reduces the oxidation stability of MEPKO. These results prove that methyl esters can be used as a substitute to replace mineral oils in power transformers. Furthermore, they show that NP can be used mainly in areas of transformer where solid insulation is subjected to high thermal and electrical stress, and TUK other places where solid insulation is required. Such combination could assure money savings and a better preservation of the oil viscosity.

Aging Effect on Characteristics of Oil Impregnated Insulation Paper for Power Transformers

This paper deals with experimental investigations of the electrical and physical properties of oil impregnated insulation paper for power transformers at different temperatures. The ac breakdown voltage, tensile strength and water content of insulation papers impregnated in mineral oil for different time periods were investigated. The effect of insulation paper thickness on the electrical and mechanical properties has also been studied. The results showed that the breakdown voltage and the tensile strength decreased with increasing the time of immersion of insulation paper in oil at room temperature, at 5℃ and at -12℃. Also, the thermal aging effect on the characteristic of insulation paper has been studied. It was found that high temperatures affect the breakdown voltage and the tensile strength to a great extent.

Improvement on the breakdown voltage for silicon-on-insulator devices based on epitaxy-separation by implantation oxygen by a partial buried n^+-layer

A novel silicon-on-insulator （SOI） high-voltage device based on epitaxy-separation by implantation oxygen （SIMOX） with a partial buried n＋-layer silicon-on-insulator （PBN SOI） is proposed in this paper. Based on the proposed expressions of the vertical interface electric field, the high concentration interface charges which are accumu- lated on the interface between top silicon layer and buried oxide layer （BOX） effectively enhance the electric field of the BOX （EI）, resulting in a high breakdown voltage （BV） for the device. For the same thicknesses of top silicon layer （10 μm） and BOX （0.375 μm）, the EI and BV of PBN SOI are improved by 186.5% and 45.4% in comparison with those of the conventional SOI, respectively.

冷热冲击下纳米粒子改性硅橡胶/环氧树脂绝缘修复涂料耐电特性

为解决现有绝缘修复材料在大范围温度波动时出现绝缘件剥落、二次开裂、电气失效等问题,研制了多种纳米粒子填充的硅橡胶/环氧树脂复合修复涂料,对比分析了冷热冲击循环前后修复涂料的粘合强度、电气性能和微观结构。结果表明:冷热冲击会造成修复涂料分子主链断裂,产生低分子产物和氧化游离基团,导致涂料相对介电常数和介质损耗增大,击穿场强减小;而功能纳米母粒可提高界面结合能,阻碍聚合物分子的拉伸和扭转,使涂料具有相对稳定的化学结构,可防止冷热冲击下基体内局部劣化通道的延伸,从而有效抑制修复涂料耐电性能的下降;当玻璃纤维、纳米ZnO、SiO_(2)共混,填充量(质量分数)为16%时,涂料电气性能良好,且硅橡胶/环氧树脂复合修复涂料固化时间短,无溶胀现象发生,附着力良好,为设备绝缘快速修复提供可能。

柔直换流阀用相变冷却工质击穿特性研究

相变冷却技术冷却效率高、安全可靠,有望攻克柔直换流阀散热瓶颈,实现其高压、大容量发展,在换流阀冷却领域具有良好的应用前景。为实现相变冷却换流阀绝缘系统可靠设计,该文设计研制了三相态相变冷却工质可调频绝缘特性测试专用平台,并以换流阀用相变冷却工质为研究对象,依据换流阀典型运行工况,利用专用测试平台开展了相变冷却工质三相态、50~300 Hz频率范围的绝缘击穿特性研究。得到了相变冷却工质击穿特性随工质相态及电压频率的变化规律,分析了相变冷却工质不同相态的击穿机理,揭示了工质相态和电压频率变化对冷却工质击穿特性的影响机制。研究工作不仅解决了高频下相变冷却工质的三相态耐压测试方法问题,且所得研究成果为相变冷却柔直换流阀的绝缘设计奠定了基础,同时可指导相变冷却技术在其他电力电子器件及装备上的应用。

SOI高压LDMOS器件氧化层抗总电离剂量辐射效应研究

绝缘体上硅(SOI)高压横向扩散金属氧化物半导体(LDMOS)器件是高压集成电路的核心器件,对其进行了总电离剂量(TID)辐射效应研究。利用仿真软件研究了器件栅氧化层、场氧化层和埋氧化层辐射陷阱电荷对电场和载流子分布的调制作用,栅氧化层辐射陷阱电荷主要作用于器件沟道区,而场氧化层和埋氧化层辐射陷阱电荷则主要作用于器件漂移区;辐射陷阱电荷在器件内部感生出的镜像电荷改变了器件原有的电场和载流子分布,从而导致器件阈值电压、击穿电压和导通电阻等参数的退化。对80 V SOI高压LDMOS器件进行了总电离剂量辐射实验,结果表明在ON态和OFF态下随着辐射剂量的增加器件性能逐步衰退,当累积辐射剂量为200 krad(Si)时,器件的击穿电压大于80 V,阈值电压漂移为0.3 V,器件抗总电离剂量辐射能力大于200 krad(Si)。

预电离间隙在不同气体介质中的正负极性击穿特性

针对自触发预电离开关在不同电压等级下应用不同气体介质的需要,以及在双边驱动电磁脉冲模拟器中加载正负极性脉冲的需求,研究了预电离间隙在N_(2)、N_(2)/SF_(6)混合气和SF_(6)中正负极性下的击穿特性。研究了不同介质中间隙的击穿电压和时延随气压的变化规律,对比了正负极性下的间隙击穿特性。研究结果表明,在本文实验条件下,预电离间隙在N_(2)中的击穿过程相对更为稳定,且N_(2)中击穿电压随气压变化线性度最佳。相比N_(2)和混合气,间隙击穿电压仅在SF_(6)中随气压增大呈现饱和趋势。在一定气压范围内,N_(2)在负极性下的击穿电压略高于正极性,混合气和SF_(6)中负极性下的击穿电压明显高于正极性,间隙的击穿过程具有一定的极性效应。相比混合气和N_(2),间隙在SF_(6)中的正负极性击穿电压绝对差值和击穿时延绝对差值都相对较高,为减小双边自触发预电离开关的同步时延差,应首选N_(2)为预电离间隙的绝缘介质。在工程应用中需考虑极性效应和不同气体介质对预电离间隙击穿特性的影响。

LDPE在植物绝缘油和矿物绝缘油中的直流击穿特性研究

随着特高压远距离输电的大规模建设,植物绝缘油取代矿物绝缘油可能成为未来的发展趋势。为了分析不同环境下低密度聚乙烯(LDPE)在不同绝缘油中的直流击穿特性的差异及原因,分别在植物绝缘油和矿物绝缘油中进行了LDPE的直流击穿实验,并通过仿真分析绝缘油放电过程对于LDPE试样击穿的影响。结果表明:LDPE在植物绝缘油中的电气强度明显高于在矿物绝缘油中的击穿强度;两种绝缘油中,试样的沿面闪络特性及击穿点位置也有不同。植物绝缘油放电产生的场强较小,因而植物绝缘油中的LDPE电气强度更高;绝缘油放电过程的差异也是沿面闪络特性及击穿点位置产生差异的原因。

10 kV电缆中间接头受潮XLPE-SiR绝缘界面放电演化分析

10 kV电缆中间接头交联聚乙烯硅橡胶(XLPE-SiR)绝缘界面在受潮条件下的放电行为严重影响配电网的可靠性,鉴于对绝缘界面放电行为的发展和特征研究较少,分析在受潮条件下10 kV电缆中间接头XLPE-SiR绝缘界面的放电行为,从仿真和试验2个方面验证XLPE-SiR绝缘界面的击穿过程。结果表明:在水分的作用下,XLPE-SiR绝缘界面会出现局部放电,并逐步演变为电弧放电。放电会产生2个影响:一方面引起绝缘材料的热解,形成电痕;另一方面,放电产生的热量导致水蒸发,有效地阻止了绝缘界面处放电的继续。随后,在存在电痕的情况下,进一步研究XLPE-SiR绝缘界面的放电行为。结果表明,当XLPE-SiR绝缘界面存在电痕时,水分的存在会迅速导致绝缘界面击穿。10 kV电缆中间接头绝缘界面受潮直接决定了其绝缘界面放电—短路故障的发展过程,因此在实际电缆中间接头的生产及施工工艺中需要加强防水管控。

机械应力影响环氧树脂绝缘电树枝劣化研究进展

环氧树脂凭借其优异的电气绝缘、耐热与机械性能以及良好的可塑性,被广泛应用于支撑绝缘子、绝缘拉杆等电气设备绝缘部件。随着电气设备电压等级的提高,环氧树脂绝缘部件运行工况日趋严苛,机械应力带来的绝缘失效问题更为突出。根据国内外参考文献,文中综述了机械应力下环氧树脂电树枝劣化引发绝缘击穿现象的研究进展。根据环氧树脂承受应力的不同,介绍了拉伸、压缩应力下电树枝生长的形貌特征,总结了温度工况下机械应力对电树枝生长的影响规律。基于环氧树脂分子链的物理微观结构与电荷输运特性,从能量角度探讨了绝缘材料在机械应力下的电树枝劣化机理。阐述了电气设备环氧绝缘部件的电树枝研究的关键问题与解决思路,为开发高绝缘性能的环氧树脂绝缘材料提供了参考。

中波自立塔绝缘瓷座被击穿罕见故障处理及分析

我台发生的中波自立塔绝缘瓷座被击穿的罕见故障是全国首例,故障应急处理和顶升塔体时依照行业标准要求,先制定方案,再严格按照流程和步骤施工,降低了施工风险。本故障与防雷设计、塔脚基础不均匀沉降、绝缘瓷座周围密封性差受潮等密切相关,警示我们依然要重视自立塔的巡检与维护工作。

高功率密度中高频变压器绝缘与散热研究进展与展望

围绕大容量电力电子变压器的发展需求,针对其中关键部件“高功率密度中高频变压器”的绝缘与散热研究进行综述分析。高功率密度对固体绝缘与散热性能提出新的挑战。首先,论述了高功率密度中高频变压器设计与应用时绝缘和散热的矛盾。其次,主要论述了高频绝缘失效的研究进展,包括绝缘击穿、局部放电、沿面放电、电树枝劣化等特性。然后,分析了目前高频绝缘的失效机理研究,包括热击穿、空间电荷效应、高频电导与自由体积效应。最后,论述了高频绝缘寿命的研究,分析了频率、温度、电压变化率du/dt等对绝缘耐电晕寿命的影响以及寿命模型。基于研究进展,提出了高频绝缘与散热的研究展望。该文综述研究对大容量电力电子变压器的设计与应用具有重要意义。

诱导触发型气体间隙开关快速绝缘恢复特性

气体间隙开关动作迅速、结构简单,在电力系统中应用前景良好,但对其绝缘恢复特性研究尚少。为此,文中采用双脉冲法研究开关间隙距离、触发介质气压及其种类对气体开关绝缘恢复特性的影响规律。结果表明:诱导触发型气体间隙开关绝缘恢复经历过渡期、快速恢复期和饱和期3个阶段,饱和期的持续时间远大于前两阶段之和,且在快速恢复期无“平台现象”出现。减小开关间隙距离,气体开关绝缘恢复速率渐进增大,其绝缘基本恢复时间(绝缘恢复系数R_(U)>90%)可降低50%。触发介质气压对气体开关绝缘恢复特性影响显著,对绝缘恢复过程的影响特性存在差异。增大触发介质气压会减缓气体开关的绝缘恢复过程,0.1~0.3 MPa压缩干燥空气中,气体间隙开关绝缘基本恢复时间对应为11~40 ms。强电负性SF_(6)对气体开关绝缘恢复具有明显增强作用,其绝缘恢复速率接近于空气中的4倍。研究结果可为气体间隙开关快速绝缘恢复技术提供理论指导。