基于脉冲电压法的10kVXLPE电缆绝缘诊断非线性分析(英文)

The diagnosis of water trees of cable insulation is of great importance as the water-treeing is a primary cause of aging breakdown for the middle voltage cables. In this paper, it is described how the water-tree-aged 10 kV XLPE cables were diagnosed. The cables were subjected to electrical stress of 5.9 kV/mm and a thermal load cycle in a curved water-filled tube for 3, 6 and 12 months of aging in accor- dance with the accelerated water-tree test method. The aged cables were used as the samples for water-tree diagnosis. First, the water-tree degraded cable, was charged by a DC voltage, and then the cable was grounded while a pulse voltage was applied to it for releasing the space charge trapped in the water trees. The amount of the space charge, which corresponds to the deterioration degree of the water trees, was calculated. The effects of DC voltage amplitude, pulse voltage repetition rate and aging conditions on the amount of the space charge were studied. Obtained results show that the amount of the space charge has a positive correlation with the applied DC voltage and the ag- ing time of the cables, and that a peak value of space charge appears with the increase of the pulse voltage repetition rate. An optimum pulse voltage repetition rate under which the space charge can be released rapidly is obtained. Furthermore, the releasing mechanism of space charge by the pulse voltage is discussed. Accumulated results show that the presented method has a high resolution for the diagnosis of water tree degradation degree and is expected to be applied in practice in future.     

油纸绝缘状态评价模型的改进(英文)

Identification of the aging condition and the failure probability of oil-paper insulation in transformer is important for improving the reliability of electric power transmission system and applying life cycle cost (LCC) management to electrical equipment. Based on data obtained in a series of multi-accelerated-aging experiments, two approaches for calculating failure probability of oil-paper insulation were compared in aspects of degree of polymerization (DP) and condition ranking. In the experiments, mineral oil and cellulose paper are sub- jected to electrical and thermal stresses, and several parameters, including dissolved gases’ volume fraction, furfural content, moisture content, and degree of polymerization, are measured after the aging process. Results show that weight of carbon oxide, which has a close relationship with cellulose paper degradation, is much higher in DP model than in condition ranking model. Moreover, it is concluded that DP model is more practically accurate than condition ranking model, because aging of cellulose paper rather than mineral oil is the key and critical factor of oil-paper insulation aging.     

交、直流电场作用下交联聚乙烯中的空间电荷习性

Polyethylene is one of the widely studied polymeric insulation materials,which have been used extensively for cable insulation.One of the major issues related to polymeric materials is its easy formation of space charge,a high chance to cause electric field distortions.This phenomenon is more significant under high voltage direct current(HVDC)stresses.Space charge can also be observed under high voltage alternative current(HVAC)stresses but with much less intensity due to the limited charge injection period and the effect of charge recombination caused by the constantly variance of the external fields.When considering the situation of an AC voltage combined with a DC offset,a possible scenario in HVDC technology,there was little research on charge dynamics in the insulation in terms of both experimental and simulation work.In this paper,a numerical simulation based a bipolar charge injection/transport model is used to obtain characteristics of space charge in polyethylene under the combined AC and DC high voltage at room temperature.The bipolar charge injection/transport model,which is widely used in HVDC space charge simulation,is applied in the combined conditions.The overall applied voltage,consisted of root mean square(RMS)values of the AC voltage and DC voltage,is kept the same,while the DC component’s voltage ratio and AC component’s frequency are changed respectively,to illustrate their effects on the space charge dynamics within the insulation under combined electric fields.The simulated charge distributions present notable differences when DC offset is increasingly added in,while relatively small differences when AC component’s frequency altering,especially for the cases whose frequency exceeding 0.5 Hz.     

交、直流电场作用下交联聚乙烯中的空间电荷习性（英文）

Polyethylene is one of the widely studied polymeric insulation materials,which have been used extensively for cable insulation.One of the major issues related to polymeric materials is its easy formation of space charge,a high chance to cause electric field distortions.This phenomenon is more significant under high voltage direct current(HVDC)stresses.Space charge can also be observed under high voltage alternative current(HVAC)stresses but with much less intensity due to the limited charge injection period and the effect of charge recombination caused by the constantly variance of the external fields.When considering the situation of an AC voltage combined with a DC offset,a possible scenario in HVDC technology,there was little research on charge dynamics in the insulation in terms of both experimental and simulation work.In this paper,a numerical simulation based a bipolar charge injection/transport model is used to obtain characteristics of space charge in polyethylene under the combined AC and DC high voltage at room temperature.The bipolar charge injection/transport model,which is widely used in HVDC space charge simulation,is applied in the combined conditions.The overall applied voltage,consisted of root mean square(RMS)values of the AC voltage and DC voltage,is kept the same,while the DC component’s voltage ratio and AC component’s frequency are changed respectively,to illustrate their effects on the space charge dynamics within the insulation under combined electric fields.The simulated charge distributions present notable differences when DC offset is increasingly added in,while relatively small differences when AC component’s frequency altering,especially for the cases whose frequency exceeding 0.5 Hz.     

交直流复合电压下油纸绝缘气隙局部放电与产气特性分析(英文)

Oil-paper insulation is used within most of high voltage direct current(HVDC) converter transformers.Partial discharge(PD) in oil-paper insulation is a major reason for the development of internal faults in HVDC converter transformer,while PDs in oil-paper insulation mainly occur in terms of gas cavity discharges.There are few study results on the development characteristics of partial discharges in oil-paper insulation and dissolved gases in oils of HVDC converter transformers.Based on a gas cavity discharge model of oil-paper insulation,the present study investigates the development characteristics of partial discharges under AC-DC combined voltages and emphatically examines the variation characteristics of dissolved gases in the discharge development process.Experiment and analysis results show that the characteristics of partial discharges and dissolved gases in oils under AC-DC combined voltages are appreciably different with those under AC voltage.These results provide theoretical support for further research on partial discharges and on dissolved gases of other internal insulating defects and are helpful for the fault diagnosis of HVDC converter transformers.     

交直流复合电压油纸绝缘的沿面局部放电特性(英文)

The valve side windings of converter transformers bear AC, DC, impulse, and reversal-polarity voltages during operation, which could result in serious insulation problems of the equipment. By performing experiments with surface discharge model of oil-paper insula- tion at 80 ℃ under combined AC-DC voltage for 200 h, we studied the spectrums and statistical parameters of partial discharges at different discharge stages. Furthermore, some fingerprint parameters were calculated in order to estimate the development situation of par- tial discharge, while the characteristic gases dissolved in the transformer oil were measured by gas chromatography. The surface discharges in the experiments were observed using a high speed camera, and a full discharge process could be marked off into four stages as follows. ①The elementary stage. When a partial discharge occurs near electrodes, electrical charges are injected into the region near electrodes and causing bubble generation. ②Due to their high resistivity and low dielectric constant, the bubbles would bare the major part of the voltage applied to samples. Therefore, discharge happens inside the small bubbles, and it emits a lot of light. ③Micromolecules of gas are produced in discharge, and further ionization in the transformer oil takes place simultaneously when high-energy electrons collide with oil molecules. ④The carrier charge moves forward to electrodes driven by the applied electric field, till they neutralize with the charge from electrodes, and hence discharge channels are formed subsequently.     

电力变压器介质响应的测量与分析(英文)

This paper discusses approaches to measure moisture in power transformers by analyzing the dielectric response of the main insulation. Dielectric diagnostic methods deduce moisture in the solid insulation from dielectric properties like polarisation depolarisation currents and dissipation factor vs. frequency. A new instrument "Dirana" combines time domain (PDC) and frequency domain (FDS) measurements and thus substantially shortens the measurement duration. New software was developed which bases on a new data pool,measured at new and aged pressboard samples with various moisture contents and oil impregnation. Its analysis algorithm compares measurements from a transformer to modelled dielectric responses,obtained from the so-called XY-model. To avoid overestimation of moisture for aged transformers,the analysis algorithm compensates for the influence of conductive aging by-products. Moisture especially increases the losses in the low frequency range of the dielectric response of pressboard. Thus,data on the left-hand side of the area dominated by interfacial polarization (insulation geometry) are required for reliable moisture determination. Case studies illustrate the application of moisture determination by dielectric response methods.     

电压响应方法在电力变压器状态评估中的应用

Power transformer is one of the most important equipment in the power system.Its operating condition affects the reliability of power supply directly.Therefore,in order to guarantee transformer operation safely and reliably,it is necessary to assess condition of power transformer accurately.Return voltage method based on voltage response measurements is still a new non-intrusive diagnosis method for internal insulation aging of transformer.In this paper the technique and application of return voltage measurement and some results of voltage response measurements of several transformers was introduced.Voltage response measurements were performed on various transformers with different voltage grades,various operating periods,different moisture contents and aging degrees on site.Derived moisture contents from return voltage measurement were compared with the corresponding moisture contents obtained from the analysis of oil samples.Based on on-site experiments and theoretical analysis,the criteria for insulation state of transformer are proposed.Moisture condition of transformer insulation can be determined by using return dominant time constant,and a good correlation between aging degree and the return voltage initial slopes of the aged transformers.Field test performed on several transformers,its interpretation of results are also presented,which proves that return voltage measurements can be used as a reliable tool for evaluating moisture content in transformer insulation.     

用于现场老化交联聚乙烯电力电缆的降解评估参数（英文）

The cables are more likely to deteriorate after several years of service in Shanghai,a city with a humid climate and abundant rainfall.Before assessing the aging status of those cables,it is critical to present effective test parameters which are sensitive to the aging process under special field conditions.Therefore,we have performed water tree investigation,tensile test,and differential scanning calorimetry(DSC)test on hundreds of cable samples removed from service.A large number of typical bowtie water trees were found in cable insulation and the water tree content was proposed to characterize the degree of water treeing.Based on Arrhenius Equation and equivalent thermal history parameters estimated from DSC profiles,we also proposed a new parameter ln(t/τθ)to characterize the aging status of cable insulation,Where,t is treated duration andτθis the thermal life under treated temperature.The applicabilities of water tree content,tensile strength,and ln(t/τθ)are tested using the analysis of variance(ANOVA).Then we investigated the relationship between the tensile strength and the water tree content using regression analysis,and analyzed the relationship between ln(t/τθ)and the tensile strength.The results indicated that each of these parameters performs differently with cables which experienced different degrees of age related degradation,and can be used to identify the aging status of field aged cables.The tensile strength can reflect the water treeing condition of field aged cables very well as a commonly used functional parameter.Since ln(t/τθ)is strongly related to the tensile strength,it is an effective parameter to characterize the aging status of field aged cable insulation.Using this newly proposed parameter is more time saving because of the convenience in sampling.     

用于现场老化交联聚乙烯电力电缆的降解评估参数

The cables are more likely to deteriorate after several years of service in Shanghai,a city with a humid climate and abundant rainfall.Before assessing the aging status of those cables,it is critical to present effective test parameters which are sensitive to the aging process under special field conditions.Therefore,we have performed water tree investigation,tensile test,and differential scanning calorimetry(DSC)test on hundreds of cable samples removed from service.A large number of typical bowtie water trees were found in cable insulation and the water tree content was proposed to characterize the degree of water treeing.Based on Arrhenius Equation and equivalent thermal history parameters estimated from DSC profiles,we also proposed a new parameter ln(t/τθ)to characterize the aging status of cable insulation,Where,t is treated duration andτθis the thermal life under treated temperature.The applicabilities of water tree content,tensile strength,and ln(t/τθ)are tested using the analysis of variance(ANOVA).Then we investigated the relationship between the tensile strength and the water tree content using regression analysis,and analyzed the relationship between ln(t/τθ)and the tensile strength.The results indicated that each of these parameters performs differently with cables which experienced different degrees of age related degradation,and can be used to identify the aging status of field aged cables.The tensile strength can reflect the water treeing condition of field aged cables very well as a commonly used functional parameter.Since ln(t/τθ)is strongly related to the tensile strength,it is an effective parameter to characterize the aging status of field aged cable insulation.Using this newly proposed parameter is more time saving because of the convenience in sampling.     

水分含量对植物油纸绝缘老化降解的影响(英文)

Natural ester is a kind of fire-resistant and environmentally friendly dielectric liquid, which has already been widely used in power transformers. The influence of moisture content on the degradation of natural ester (camellia oil and FR3 oil) impregnated paper in- sulation was investigated and compared with that of mineral oil impregnated paper in this paper. The initial moisture contents of insulating paper samples were 0.3%, 2% and 4%, respectively. Thermal aging experiment was conducted at 130 °C in hermetical stainless vessels for 80 days. Aging parameters such as the degree of polymerization (DP) of insulating paper, furfural mass concentration in oil and acid number of oil were measured. Chain scissions number (CSN) of aged insulating paper was calculated. The results show that moisture could accele- rate the degradation of both natural ester impregnated paper insulation and mineral oil impregnated paper insulation, while the degradation rate of natural ester impregnated paper insulation is much lower than that of mineral oil impregnated paper insulation. High moisture satura- tion solubility and hydrolysis process of natural ester may be the reason.     

油纸绝缘状态对变压器油油流带电的影响(英文)

This contribution is not only intended to provide a fresh review for researches on static electrification, but also contains a sub- stantial amount of new material with a view of closing some gaps in the present state of knowledge of oil streaming electrification. In this paper, the Electrostatic Charging Tendency (ECT) of fresh (unaged) and aged transformer oils were investigated in a spinning disk system. Static electrification measurement at different aging degrees was carried out under laboratory controlled conditions. Changes in static elec- trification were compared to some classical aging indexes (conductivity, dissipation factor, water content, resistivity, etc.). Fast, inexpensive and reliable laboratory testing procedures developed by American Society for Testing Materials (D 6802 and D 6181) were also used to monitor decay products as trace impurities. The obtained results show that static electrification currents increase with temperature, fluid mo- tion velocity, surface properties and the aging byproducts of the oil. The polarity, the amplitude and the time constant of the electrification currents are also affected. The results show that static electrification has relationship with thermal aging and is sensitive to turbidimetric and spectrophotometric measurements.     

操作过电压对电缆绝缘电老化的影响(英文)

Due to the insufficient information regarding the aging phenomenon of cables caused by switching impulses, we aged 15 kV XLPE and EPR cable samples by 10 000 switching impulses in experiments and tested them. Plus in order to compare the aging phenome- non under multi-stress conditions, additional EPR cable samples were aged by rated AC voltage and current with switching impulses superimposed. We used measurements of partial discharge parameters to monitor the cables’ conditions during their aging process, and the AC breakdown voltages measurement to evaluate the cables after aging. Moreover, the Fourier transform infrared (FTIR) spectroscopy measurements revealed the changes of insulation materials after aging. The measurement results confirm that the accelerated aging of cable samples had taken place. The impacts of each individual aging factor are shown through the selected measurements and comparison. The study also helps to assess the reliability of the XLPE and EPR cables under similar condition while serving in power systems.     

基于状态监测与系统风险的老化变压器更新策略

This paper presents a replacement strategy for an aged transformer based on condition monitoring and system risk.The condition monitoring measurements are used to estimate the insulation age of the transformer.The unavailability because of transformer aging failure is calculated using the insulation age instead of the traditional natural age.The system risk is assessed using the total unavailability from both aging and repairable failures.The expected damage cost and benefit due to delaying the replacement of the transformer are evaluated.The best replacement timing is determined as the year when the replacement of the transformer reaches the maximum net benefit.A case study for two aged transformers in a utility system demonstrates the effectiveness of the proposed method.     

多层有机绝缘结构真空沿面闪络特性和机理研究(英文)

In order to further investigate the surface flashover mechanism in vacuum, the surface flashover and electric field distribution of multilayer organic insulation structure are studied and developed based on the previous studies. The samples of multilayer organic insulation structure are prepared by inserting multilayer organic composite material with different relative permittivity between the electrode and the dielectric. Two multilayer organic insulation structures are prepared in this study. One is the cylindrical samples, the other is 45° samples. The impulse (1.2/50 μs) and DC flashover voltages in vacuum are tested, and the electric field distributions of two insulation structures are analyzed by ANSYS. It is found that these two insulation structure could effectively improve the surface flashover performance in vacuum. The results indicate that the highest impulse first flashover voltage of cylindrical samples reaches 65 kV and increases by 25% under im- pulse voltage. The highest first flashover voltage of /c samples reaches 81 kV and increases by 32% under impulse voltage. The results of electric field simulation demonstrate that different mechanisms exist between 45° insulation structure and cylindrical structure.     

陷阱参数及其与交联聚乙烯电缆绝缘状态

Space charge issues have raised many attentions in recent years,especially in high voltage direct current(HVDC)application.Space charge accumulation in insulation system will give rise to acceleration of ageing and even cause premature failure of the material.However,from another angle,space charge might be also considered as a diagnostic tool of ageing for insulation materials.In this paper,a trapping-detrapping model has been developed to estimate trapping parameters of cross-linked polyethylene(XLPE)cable sections,which were taken from different HVAC operation conditions of 12 years and 8 years.The results reveal that,for both cable sections,samples from the inner location have the greatest trap density and the deepest trap depth.Additionally,breakdown strength tests and FTIR(Fourier-transform infrared)measurements on those samples have been carried out.From FTIR measurement results,the degree of oxidation among three layers could be found by the carbonyl index values.The oxidation degree of aged cable at the outer layer is higher than that at the other two layers probably because of the most sufficient contact with oxygen.Also,it has been noticed that the results from these measurements show some correlations with the estimated trapping parameters,especially for breakdown strength.     

TiO2纳米粒子对矿物及植物纳米变压器油中电荷输运特性的影响（英文）

TiO2 semiconductive nanoparticles are added into mineral and ester based transformer oil to form semiconductive nanofluids (SNFs) with the aim of enhancing the oil’s insulating performance. Charge accumulation and decay characteristics of both pure oils and SNFs are measured by pulse electroacoustic (PEA) technique. The result reveals that compared with pure oil, SNFs have more uniform in- ternal electric fields with voltage applied and higher charge decay rate after removing the applied voltage. This is caused by the increase of shallow trap density in SNFs, due to the test results of thermally stimulated current (TSC). It is proposed that the electron trapping and de-trapping processes in shallow traps could be the main charge transport processes in the nanofluid transformer oil.     

船用电缆绝缘老化实验及剩余寿命预测方法(英文)

In order to evaluate the remaining lifetime of shipboard cables, accelerated aging experiments of cable insulation layers were conducted on a test bed, which is developed to simulate the shipboard environment. Two groups of aging experiments (with and without humidity) were conducted, and the elongation at the break of aged cable insulation layer samples was measured. The aging curves of CXF type cable’s insulation layers under 70~90 °C were plotted, based on which a corresponding mathematical models was developed according to Arrhenius theory. Using this mathematic model, the remaining lifetime of CXF type shipboard cable can be predicted. The proposed method is a new way to evaluate cables’ remaining (useful) lifetime.     

锦屏—苏南±800kV特高压直流输电工程直流滤波器的暂态额定计算(英文)

DC filter components and devices in converter stations of a high voltage DC transmission project may withstand a certain amount of transient overvoltage due to the impact of transient impulses.In order to protect them,suitable arresters should be equipped properly in the filters to limit the transient overvoltage to an acceptable level.By utilizing the method of DC filter simulation and transient calculation model,the paper studies the transient overvoltage in the DC filters of the Jinping-Sunan ultra high voltage direct current(UHVDC) transmission project under the most severe transient operation conditions.Three arresters are installed inside each filter,which consequently decide the insulation levels of the filter component: mainly capacitors,reactors and resistors.The lightning impulse insulation levels for the high voltage reactors of the two filters are 648 kV and 788 kV respectively,while they are 464 kV and 627 kV for the low voltage reactors,and 648 kV and 788 kV for the resistors.The insulation level for the high voltage capacitors is no more than 815 kV.The calculation results provide basis for choice of the DC filter components.     

HVAC输电线路损耗和空间电场的改进计算方法（英文）

An improved method for calculating the corona power loss and the ground-level electric field on HVAC transmission lines induced by corona is proposed.Based on a charge simulation method combined with a method of successive images,the proposed method has the number and location of the simulated charges not arbitrary.When the surface electric field of a conductor exceeds the onset value,charges are emitted from corona into the space around,and the space ions and the surface charges on each sub-conductor are simulated by using the images of the other sub-conductors.The displacements of the space ions are calculated at every time step during corona periods in both the positive and the negative half cycles.Several examples are calculated by using the proposed method,and the calculated electric field at the ground level and the corona power loss agree well with previous measurements.The results show that simulating 12 charges in each conductor during 600 time steps in one cycle takes less time while guarantees the accuracy.The corona discharge from a 220 kV transmission line enhances slightly(less than 2%) the electric field at the ground level,but this effect is little from a 500 kV line.The improved method is a good compromise between the time cost and the accuracy of calculation.