高电压多脉冲冲击下单片与双片并联的MOV性能

采用幅值为20 kA、时间间隔为50 ms的同时序冲击高压5脉冲分别对单片氧化锌压敏电阻元件、2片压敏电压相差10 V、2片压敏电压相同的并联压敏电阻进行冲击试验。试验表明单片压敏电阻难以承受多脉冲的大能量,将幅值为40 kA同样的波形施加在2片压敏电阻并联上时,2片压敏电压相同的压敏电阻并联耐受冲击次数是单片情况下的2倍,而压敏电压相差10 V的2片压敏电阻并联的耐受冲击次数甚至比单片少。通过对多脉冲冲击下的压敏电阻片电气参数、温度测试分析以及外观损坏形式分析,认为多脉冲情况下的损坏机理主要以热击穿为主。     

Electrical parameter statistic analysis and parallel coordination of ZnO varistors in low-voltage protection devices

Analyzing the nonuniformity of electrical parameters of ZnO varistors is useful to select and coordinate the ZnO varistors in parallel operation and improve the protection capability of surge-protection device (SPD). The nonuniformity of 1-mA dc voltage and impulse residual voltage of commercial low-voltage ZnO varistors were estimated by statistic analysis in this paper. The Minimum Gobble Distribution was used to describe the distribution of 1-mA dc voltage and impulse residual voltage, ZnO varistors were verified conforming to the Minimum Gobble Distribution by the Kolmogorov-Smirnov test. The relationship between the impulse residual voltage and 1-mA dc voltage has a chaos phenomenon, and they have a close relative degree by t-test, the impulse residual voltage can be estimated by voltage ratio and 1-mA dc voltage. The nonuniform phenomena of electrical parameters of ZnO varistors were simulated by Voronoi network. The current overload of ZnO varistor with reduced residual voltage is serious, in order to keep safe operation of SPDs, when we design a SPD with ZnO varistors in parallel, a safe margin coefficient of discharge withstand current should be considered according to the actual relative standard deviation of surge residual voltages of used ZnO varistors.     

Analysis of ZnO varistors prepared from high-energy mechanical activation

ZnO varistors were prepared by high-energy mechanical activation to study its effect on the microstructure and electrical properties. Comparison of different permutation and combination of ZnO powders and additives subjected to activation for 0, 6 and 12 h were given in I–V, C–V, complex resistance study. The variation of Schottky barrier height Φ _b, donor concentration N _d, interface state density N _t and depletion layer width L were calculated in different samples. Finally, individual grain boundaries were investigated by SSPM (Scanning Surface Potential Microscopy) under in situ applied fields, allowing determination of the voltage dependence of grain boundary electronic properties.     

高压直流电路的开断及其能量吸收

本文通过理论分析阐明了吸能装置在直流开断过程中的重要作用,作为算例对葛-上线的直流开断过程进行了计算分析,求得当开断电流为4000A在线路末端发生故障时,流过吸能装置的电流波形为8.8ms的矩形波,要求吸收的能量为10.29MJ。通过试验研究得出阀片在不同时间长度电流波形作用下的通流能力可以按照能量相等原则来进行换算。     

交直流老化后ZnO压敏电阻宏观电容量随时间变化的特性分析

针对ZnO压敏电阻在交、直流老化作用后,其宏观电容量随时间变化特性的问题,基于砖块模型（block model）对影响ZnO压敏电阻宏观电容量的相关参数进行了理论分析,通过对ZnO压敏电阻样品分别施加不同时长的交流以及直流老化试验时,发现ZnO压敏电阻的宏观电容量在接受交、直流老化后随着时间的延长呈现先降低后增长的趋势;当交、直流老化时间较短时,宏观电容量相较初始值存在小幅降低,而当交、直流老化时间较长时,宏观电容量相较初始值存在大幅的增长,得出宏观电容量随时间的变化是由界面态俘获电子的释放过程以及晶界层热破坏过程共同作用所导致的结论,这对研究ZnO压敏电阻的老化特性具有一定的参考价值。     

高能ZnO非线性电阻串联组合的两种算法

针对氧化锌（ＺｎＯ） 压敏电阻显著的非线性特性， 对用计算机进行ＺｎＯ 阀片串联组合的算法进行了研究。对文献［１］ 中的算法进行了改进， 消除了其在应用上的某些局限， 使其对工程实际具有更好的适用性。文中还提出了一种新的串联单柱的组合算法， 具有计算简便， 易于在计算机上实现的特点     

包封材料的改进及其对压敏电阻大电流耐受性能的影响

为了满足IEC和国标对避雷器阀片大电流冲击耐受性能指标的要求，通过对环氧树脂配方及工艺的调整，研制了新型环氧包封材料，使环氧树脂与氧化锌瓷体的热膨胀系数更加匹配，大幅度提高氧化锌压敏电阻阀片大电流冲击耐受性能。     

现场总线技术用于ZnO压敏电阻片制造电器智能化的思考

ZnO压敏电阻片制造工艺复杂,工序多,周期长,设备多,控制技术要求高,随着测量控制设备仪器的智能化水平的提高,进一步提高自动化程度,提高控制能力,减少损失。现场总线是连接智能现场设备和自动化系统的数字双向传输的通信网络,是工业过程控制、制造业等领域自动控制技术发展的热点。本文简要介绍了现场总线的主要种类和基本特点及其应用,对ZnO压敏电阻片制造的现场智能设备和仪器仪表的现地与远程控制的实现作了一些思考,利用现场总线技术实现对金属氧化物避雷器用氧化锌压敏电阻片的制造进行现地和远程自动控制,提高制造水平,提高压敏电阻片电气性能的均一性,降低分散性,避免损失。     

ZnO压敏电阻老化机理的研究进展

ZnO压敏电阻作为避雷器的关键元件在限制电力系统过电压方面具有极为重要的作用,直接决定电力系统的过电压水平和设备的绝缘水平。然而其在承受长期工作电压或短时冲击电流作用时不可避免地会产生老化现象。本文总结了国内外学者对于ZnO压敏电阻老化机理的不同观点及最新研究进展,分析了其老化机理,并讨论了提高ZnO压敏电阻稳定性的方法。     

High Temperature Characterization of Electrical Barriers in ZnO Varistors*

Two main models have been proposed to describe the potential barriers in ZnO varistors: the surface oxidation and the surface states. It has been difficult to decide which of them better corresponds to the experimental observations. High temperature electrical characterization of these materials is an important tool to understand the formation of the electrical barriers. In this work, using literature data describing ZnO varistor characteristics at high temperature, up to 1153°C, we calculate the energy position of the equilibrium Fermi level at the grain boundary interface, and found that this parameter decreases with the increase of temperature, and for temperatures higher than ～700°C it stays close to the ZnO band gap without crossing it. This behavior shows that the interface never presents a p-type character, a starting point to develop the surface states model. On the other hand, 700°C is a temperature too low for the surface oxidation mechanism to be operative. It is then proposed that, during cooling down to ～700°C, the interface Fermi level stays close to the middle of the band gap due to the adsorption and subsequent reaction of oxygen with ZnO surfaces/grain boundaries. For lower temperatures, when the interface Fermi level separates from the middle of the band gap, it is proposed that it follows the variation of the bulk Fermi level, which in turn is caused by shallow donors in ZnO. A calculation assuming a reduced electroneutrality condition, gave a donor density of ～ 3 × 10¹⁷ cm^-3, which corresponds approximately to the density of carriers in the material for temperatures down to room temperature. This value is in a good agreement with those available in the literature. Knowing both the bulk and the interface Fermi levels, it is then possible to calculate the barrier height at any temperature, and it is observed that it is almost constant from room temperature up to ～400°C, with a value of 0.8 eV, and than decreases monotonously up to 1153°C. Taking these values, it is possible to calculate the variation of the low voltage conductivity with temperature, and it is found that, apart from the variation between room temperature and 400°C, with no special significance, the decrease of the barrier height from 400°–1153°C induces an extra change of the conductivity from which a fictitious activation energy of 1.5 eV is obtained. Therefore, these two energies are not related to shallow and deep donors in ZnO grains.     

考虑微观特性的ZnO压敏电阻计算模拟模型

电力设备的绝缘水平建立在避雷器的过电压保护水平基础之上。ZnO压敏电阻具有优良的非线性电压-电流特性和浪涌能量吸收能力,被广泛用作电力系统避雷器的核心元件。ZnO压敏电阻的电气特性由其复杂的微结构和晶界特性决定。该文以Voronoi网络模型为基础,建立ZnO压敏电阻的微观结构模型。采用考虑晶间旁路效应的晶界分区模型,建立求解氧化锌压敏电阻宏观电气性能的大规模非线性电阻网络方程。针对难以采用常规牛顿迭代方法求解的问题,提出基于分段线性化和差分重构的快速求解优化算法,计算结果误差指标在10-3数量级以下。采用模型计算得到了尖晶石含量、晶粒尺寸不均匀度以及气孔率等微观结构参数对ZnO压敏电阻宏观电气性能的影响规律。     

氧化锌压敏电阻器的工频过电压（TOV）特性

本文就氧化锌压敏电阻器的工频过电压特性（以下称TOV特性）的重要性、正确表征和影响因素展开讨论。提出TOV特性应以TOV幅值及对应的耐受时间来表述,称为TOV耐受时间特性,作为给SPD应用的氧化锌压敏电阻器的设计应用资料,则应提供两个数据,一是TOV耐受时间特性,二是暂态过电压施加时温度随时间变化数据。氧化锌压敏电阻器的TOV耐受时间特性,直接与耐受TOV能量的能力以及TOV工作区（1mA～10A）V-I特性曲线相关,制约耐受TOV能量的能力的因素,是配方与工艺引起的晶相差异和结构的均匀性,以及热稳定性。TOV工作区（1mA～10A）V-I特性曲线,除了受配方与工艺影响外,还受工作历史的影响。电阻体均匀性好的TOV特性好,而TOV工作区（1mA～10A）V-I特性曲线非线性差或电压正温度数引起加载TOV时电流变小,可以提高TOV耐受时间。     

ZnO压敏电阻在高压变频器过电压保护中的应用

基于IGCT串联中性点钳位三电平高压变频器过电压保护进行研究,首次提出了利用氧化锌(ZnO)压敏电阻对高压变频器进行过电压保护的方法。通过分析ZnO压敏电阻的各种放置位置和接线形式,得出了合理的设计方案。以逆变系统整体作为变频器过电压保护的对象,解决了单个电力电子开关器件过电压保护困难的问题。结合实际的变频器参数,详细分析逆变系统工作状态的耐压情况,设计了ZnO压敏电阻。通过Matlab/Simulink对过电压情况的仿真,验证了所设计的ZnO压敏电阻对中性点钳位三电平高压变频器过电压保护的有效性。本文所设计的ZnO压敏电阻已得到实际应用。     

Influence of different nano titania on microstructure and electrical properties of low voltage zinc oxide varistors

A series of check experiments showed that ZnO varistors doped with TiO₂ of different particle sizes and dispersing states have different densities, porosities and grain morphologies, which relate to their electrical properties tightly. Compared with samples added with TiO₂ dopants of others types, the varistors added with nm-TiO₂ sol exhibit large density, low porosity, big granular size, low breakdown voltage gradient and small leakage current. Hence nm-TiO₂ sol dopant is the best grain growth enhancing additive for optimizing almost all the electrical parameters.     

Passive intermodulation analysis of single contact junctions of wire mesh

Because the nonlinearity of contact junctions in a wire mesh is the main source of passive intermodulation (PIM) generation, this work aims to analyze the PIM problem of single contact junctions. This work first derives the formulas of micro-contact effects, which reveals the mathematical relationship between the contact force and the micro-contact effects for a single contact junction of a wire mesh. Then, an equivalent circuit model describing contact nonlinearity is constructed to evaluate the nonlinear current through a single contact junction. Finally, an experimental platform is built to test the current through a single contact junction of two metal wires. The PIM power levels of a single contact junction are determined by the finite difference time domain method. The comparison of PIM power levels between the theoretical and experimental results is illustrated to verify the validity of the proposed method. The research results indicate PIM is influenced greatly by the contact forces of junctions. The appropriate contact forces on junctions of wire mesh are beneficial to reduce PIM distortion.     

Impedance and Modulus Spectroscopy of ZnO Varistors

The ac response of ZnO varistors has been investigated over thetemperature range 100 to 380°C using impedance and modulusspectroscopy. Impedance spectra show only a single peak, which representsthe most resistive component in the sample and is responsible for the dcproperties, whereas an additional peak appears in the modulus spectrum. Thetwo components have temperature-dependent activation energies in the ranges,0.52–1.00 and 0.54–0.64 eV, respectively but their resistancesdiffer by 1 to 2 orders of magnitude. From their capacitance values, eachrepresents a region 100 to 500 thick; they aretentatively assigned to an electrically-active interface and anintergranular layer.     

合成套氧化锌限压器的热特性研究──第二部分：阀片功率损耗的模型及限压器的热稳定性能

在工频电压作用下氧化锌阀片的功率损耗是温度与荷电率的复杂函数。本文从试验数据中得出了其人工神经网络模型，给出了合成套氧化锌限压器的热平衡图；分析讨论了限压器的稳定工作温度、极限工作温度和极限吸收能量；１１０ｋＶ、２２０ｋＶ合成套氧化锌限压器具有很好的热稳定性；同时讨论了阳光辐射对热稳定性能的影响。     

Study on the ZnO-based ceramic films for low-voltage varistors with high stability

ZnO-based ceramic films for low-voltage varistors were fabricated by a novel sol-gel process. The stability of ZnO-based ceramic films has been studied by improving the degradation properties and increasing the microstructure compactness of the films. The degradation of the film varistors was improved via doping with Na⁺ and heat-treating in oxygen ambient. The microstructure compactness was increased via eliminating the microspores and improving uniformity of the grain size of ZnO by doping with B₂O₃. The results indicated that ZnO-based ceramic films for low-voltage varistors with high stability can be obtained while the concentration of doped Na⁺ is 20–40 ppm, B₂O₃ is 0.25–0.5 mol.% and being heat-treated in oxygen ambient for 2 h.     

High Temperature Characterization of Electrical Barriers in ZnO Varistors*

Two main models have been proposed to describe the potential barriers in ZnO varistors: the surface oxidation and the surface states. It has been difficult to decide which of them better corresponds to the experimental observations. High temperature electrical characterization of these materials is an important tool to understand the formation of the electrical barriers. In this work, using literature data describing ZnO varistor characteristics at high temperature, up to 1153°C, we calculate the energy position of the equilibrium Fermi level at the grain boundary interface, and found that this parameter decreases with the increase of temperature, and for temperatures higher than 700°C it stays close to the ZnO band gap without crossing it. This behavior shows that the interface never presents a p-type character, a starting point to develop the surface states model. On the other hand, 700°C is a temperature too low for the surface oxidation mechanism to be operative. It is then proposed that, during cooling down to 700°C, the interface Fermi level stays close to the middle of the band gap due to the adsorption and subsequent reaction of oxygen with ZnO surfaces/grain boundaries. For lower temperatures, when the interface Fermi level separates from the middle of the band gap, it is proposed that it follows the variation of the bulk Fermi level, which in turn is caused by shallow donors in ZnO. A calculation assuming a reduced electroneutrality condition, gave a donor density of 3 × 10¹⁷ cm^-3, which corresponds approximately to the density of carriers in the material for temperatures down to room temperature. This value is in a good agreement with those available in the literature. Knowing both the bulk and the interface Fermi levels, it is then possible to calculate the barrier height at any temperature, and it is observed that it is almost constant from room temperature up to 400°C, with a value of 0.8 eV, and than decreases monotonously up to 1153°C. Taking these values, it is possible to calculate the variation of the low voltage conductivity with temperature, and it is found that, apart from the variation between room temperature and 400°C, with no special significance, the decrease of the barrier height from 400°–1153°C induces an extra change of the conductivity from which a fictitious activation energy of 1.5 eV is obtained. Therefore, these two energies are not related to shallow and deep donors in ZnO grains.     

用TSC谱图研讨ZnO压敏陶瓷材料脉冲后的衰退

用热刺激电流(TSC)谱图分析法对氧化锌(ZnO)陶瓷材料的极化机理及通过对比实验对脉冲衰退机理进行了分析,讨论了热离子松弛极化、夹层极化,它们对材料损耗的影响以及脉冲电流作用引起材料一些性能参数的变化,对实验中发现的ZnO材料热释电现象给予研讨。