Dynamism of interconnected channels in water-treed polyethylene

Loss current through non-penetrated water treed polyethylene increases with exposure time at 1000 V, 500 Hz. The increment is discussed by taking the capacitance of the water treed sheet sample to be the Maxwell-Wagner type capacitor composed of two layers: the capacitance both for the non-treed region and the unfilled channel region is connected in series to the parallel combination of the capacitance and the conductance for the water-filled channel region. By assuming a non-ohmic dependence of the conductance, the fundamental and 3rd harmonic components of the loss current have been calculated numerically, based on the equivalent circuit. The numerical results give a good agreement with the observed changes of the magnitudes of fundamental and 3rd harmonic components I₁ and I₃, and their phase angles &thetas;₁ and &thetas;₃, respectively, for the exposure time. It has been concluded that the water-filled channel region in the water treed region grows with exposure time. It is also concluded that the conductivity of the water-filled channel region increases slightly with its growth     

Analysis of relaxation parameters and their distributions using fractional polarization thermally stimulated discharge currents

It is shown that, in the analysis of fractional polarization thermally stimulated depolarisation current, the values obtained for the activation energy W and the preexponential factor /spl tau//sub 0/ depend on which one is assumed constant. The elemental peak position and shape change significantly for simulations where we assume that the activation energy is variable and the preexponential factor is constant, or vice-versa. A mathematical expression for the current is proposed in the case where W /spl tau//sub 0/ and are both variable. The uncertainties affecting the relaxation parameters produce a broadening of the theoretical peak. The minimum uncertainties in the relaxation parameters are estimated. For a current peak at temperature T/sub m/, a calculated distribution of W with width /spl ap/ kTm, or a calculated distribution of /spl tau/ with width /spl ap/ /spl tau//sub 0/ is physically meaningless.     

Origins of thermally stimulated current in polyethersulfone

In order to understand the dominant carrier species in electrical conduction in polyethersulfone (PES), thermally stimulated current (TSC) measurements were carried out under various conditions. It was found that PES has two TSC peaks in the temperature range from 20 to 220°C, consisting of an α peak at ~210°C and a β peak whose peak temperature moves towards a higher temperature with an increasing poling temperature. Even when the sample was not poled, PES shows a spontaneous current with its peak at ~210°C. Both the spontaneous current peak and the α peak were found to disappear when the sample had been heated to 230°C, keeping the external circuit closed. From such similarity of appearance and disappearance between the two peaks, it is concluded that they have the same origin. From the change in the spatial distribution of space charges inside the sample measured simultaneously with the TSC measurements, positive charges, probably due to K⁺ ions, existed nonuniformly in the sample from the beginning, and are thought to be responsible for the two peaks. From a similar study, the β peak is considered to be due to polarization of ionic space charges during the poling process     

Dielectric breakdown of low-density polyethylene under simulatedinverter voltages

Breakdown characteristics have been investigated for low-density polyethylene immersed in silicone oil by applying power-frequency ac voltages with high-frequency components, which are simulated output voltages of a pulse-width-modulation inverter. It was found that the breakdown voltage decreases as the high-frequency component increases. However, the number of zero-crossings of the applied voltage, which is very influential in water-tree growth, does not seem to play an important role in the dielectric breakdown process     

水树老化XLPE电缆绝缘温度特性的研究

为了确保电力系统的安全可靠运行,运行中的XLPE绝缘电力电缆老化状态的评价和估计具有十分现实的意义。本文通过实验,研究了温度对水树老化XLPE电缆绝缘的tgδ、损耗电流谐波分量的影响,并探讨了采用电缆绝缘的交流不平衡分量来诊断电缆中水树状态的可行性。     

PD resistance of thermally aged polyethylene andcarbonyl-containing model polymers

Films of polyethylene (PE) with different degrees of crystallinity, including a crosslinked cable grade and a crosslinked grade containing 2-vinylnaphthalene, were aged in air at 373, 388 and 403 K for periods to 19000 h and subsequently exposed to external partial discharge (PD) in dry air at 298 K. Stress-strain measurements in a tensile testing machine, differential scanning calorimetry to assess the antioxidant concentration, crystallinity and crystal thickness, infrared spectroscopy to determine the concentrations of oxidation products, and size exclusion chromatography (sec) were used to characterize the samples before and after the oven aging. The thermal oxidation led to a combination of chain scission, as revealed by sec on the soluble fraction of aged samples, and crosslinking which was evident from the gel formation. Oxidation-induced chain scission increased the crystallinity of the crystal lamella stacks stable at the aging temperature, and lead to a pronounced brittleness of these materials. The fraction that was molten at the aging temperature and crystallized during the subsequent cooling phase dropped substantially in crystallinity after oxidation. Mere oxidation was not sufficient to cause a decrease in PD life, unless the carbonyl content was above a certain threshold value above which the PD life decreased rapidly with increasing concentration of carbonyl groups. It is suggested that the carbonyl groups enhance radical formation and thereby accelerate surface erosion, causing early PD breakdown. The PD life was not influenced by the degree of crystallinity, the average crystal thickness, the concentration of antioxidant or by the fracture toughness. Vinylnaphthalene acted in crosslinked PE as a stabilizer and prolonged the incubation period for oxidation     

微电流放电对免维护铅酸蓄电池性能的影响

参照模拟轿车用电器系统,选用12V-70Ah免维护铅酸蓄电池进行微电流放电实验,放电电流分别为0mA、6mA、20mA和30mA。结果表明,微电流放电实验结束后,对容量的恢复及1C20放电没有产生影响;对低温起动性能和3C20放电产生一定的影响,随着微电流放电实验中电流值的增加,影响程度更加明显。     

Calculation of thermally stimulated depolarization current fromisothermal dielectric response data

Thermally stimulated depolarization is modeled from dielectric response functions deduced from isothermal measurements. The key assumption made is that the same state of polarization can be achieved both via the real non-isothermal thermally stimulated depolarization (TSD) process and via an equivalent isothermal process. The change of polarization with temperature and time is traced through a continuous adjustment of the starting and stopping times and polarizing field of the fictitious isothermal process. The theory is applicable to general cases of non-Debye relaxation with variable activation energy. A comparison of the modeled and measured TSD thermograms is presented for films     

多针-平板电极介质阻挡放电的特性及影响因素研究

通过电压-电流波形图和电压-电荷李萨育图形的测量,研究了空气中多针-平板电极介质阻挡放电特性,比较了这种放电和平板-平板电极介质阻挡放电的区别。通过实验研究了放电间隙距离、多针电极针的密度、阻挡介质材料性质对多针-平板电极介质阻挡放电放电功率的影响。实验结果表明,在相同的条件下,与平板-平板电极介质阻挡放电相比,多针-平板电极介质阻挡放电消耗较大的放电功率;放电空间消耗的功率随外加电压和介电常数的增加而增加,随气隙距离的增加而减小。     

过放电对烧结式MH/Ni电池性能的影响

研究了强制过放电及用0.5Ω短路后,烧结式MH/Ni电池的开路电压(OCV)及性能变化.强制过放电后,电池的容量下降,经过3次循环可以恢复.0.5 Ω短路放电至0 V,对容量几乎没有影响,但OCV的恢复与微短路有关.     

板栅尺寸及结构对电池放电性能的影响

研究了板棚的外形尺寸、筋条结构及极耳位置对汽车用蓄电池放电性能的影响。     

Suppression of electrical treeing by addition of lithium carbonate to low-density polyethylene

Low-density polyethylene (LDPE) is used widely as an electric insulating material in electric power cables. The generation of electrical treeing due to aging of LDPE may lose the reliability of its insulating capability. Therefore it is important to suppress its treeing and to improve its electrical properties so that the reliability of cables can be improved. For this purpose, the authors prepared LDPE to which various inorganic materials were added. This investigation focuses particularly on lithium carbonate and quartz which were effective in suppressing the treeing when added to LDPE. Lithium carbonate-added (0.25 phr) LDPE in two hours of discharge showed the tree length 150 μm shorter than that (560 μm) of nonadded LDPE, exhibiting an obvious suppressing effect on treeing generation. It was found that this effect was more significant than quartz-added LDPE and even at elevated temperatures lithium carbonate-added LDPE exhibited suppression of treeing. The thermal decomposition temperature at which lithium carbonate-added (1 phr) LDPE loses 50 percent of its weight rose 100°C more than nonadded LDPE and 60°C more than that of quartz-added LDPE, which showed improvement in heat resistance of LDPE.     

取代元素对Mm-Ni基合金放电特性的影响

研究了Co,Mn,Al等取代元素对Mm-Ni基贮氢合金放电温度和速率特性的影响.结果表明,取代元素可提高Mm-Ni基合金氢化物的稳定性和较高温度下的放电性能,但它们对合金与氢反应的动力学特性有不同程度的损害.降低了合金在较低温度时的放电效率.使放电速率特性恶化.     

锂离子电池高倍率放电性能的影响因素

研究了18650型锂离子电池高倍率放电性能的影响因素.使用LiMn2O4/LiCoO2或LiMn2O4/LiNi1/3Co1/3Mn1/3O2的电池的放电容量保持率比使用LiFePO4的电池高;电解液电导率对电池的高倍率放电性能有明显的影响.采用D50=9μm的LiNi1/3co1/3Mn1/3O2、添加导电锂盐的电解液的电池,在25 C倍率下的放电电压平缓,放电容量为1246 mAh,循环性能良好.