高压ZnO厚膜压敏电阻的制备及导电机理分析

通过高能球磨、丝网印刷和低温烧结制备出高压ZnO厚膜压敏电阻,并对厚膜试样进行了电学性能、物相成分和微观形貌的表征。结果表明:厚膜试样电位梯度达到3 159.4 V/mm,漏电流为36.4μA,非线性系数为13.1,平均晶粒尺寸为1.29μm。高能球磨和低温烧结使厚膜试样的晶粒尺寸大大减小,有效提高了电位梯度值。分析了厚膜压敏电阻单晶界体系的导电机理,发现预击穿区势垒宽度的增加和单晶界电压的提高对其非线性性能以及压敏电压的提升影响明显,决定了压敏电阻的电学特性。     

ZnO压敏电阻片的应用研究进展

本文针对1000kV交流系统和±800kV直流系统中各种避雷器对安全可靠性、重量轻、体积小型化的要求,总结了国内外竞相开展的提高ZnO压敏电阻片电位梯度和能量吸收能力的研究开发工作。综述分析了国内外用于交直流系统避雷器的高电位梯度、大能量吸收能力的新型ZnO压敏电阻片的研究开发和应用进展,总结了提高ZnO压敏电阻片电位梯度(达4.0kV/cm)和能量吸收能力(达300J/cm3)的主要途径。     

Al2O3掺杂ZnO压敏电阻在不同烧结温度下的电气特性研究

在不同烧结温度下制备了氧化铝(Al₂O₃)掺杂的氧化锌(ZnO)压敏电阻,并对其进行扫描电子显微镜、X射线衍射、电流-电压、电容-电压测试以研究ZnO压敏电阻的微观结构和电气特性。结果表明:随着烧结温度的升高,Al₂O₃掺杂的ZnO压敏电阻泄漏电流得到了明显的抑制,这是由于施主密度和界面态密度不断增大,提高了晶界的势垒高度。而Al³⁺随着烧结温度的升高会不断地固溶入ZnO晶粒中,降低了晶粒电阻率,从而降低ZnO压敏电阻在通过大电流时的残压比。当烧结温度为1 150℃时,ZnO压敏电阻的电气特性最佳,电压梯度为418.70 V/mm,泄漏电流为0.74,残压比为1.68,非线性系数为67.5,有助于提高ZnO避雷器的保护性能,实现深度限制电力系统,特别是特高压系统的过电压。     

特高压避雷器用ZnO压敏电阻电压梯度限值的探讨

为了研制性能优异的特高压避雷器,笔者对实际所需ZnO压敏电阻的电压梯度是否存在限值进行了研究,并结合特高压避雷器的实际应用需求,详细讨论了ZnO压敏电阻的电压梯度限值的相关问题。研究表明,对适用于特高压避雷器的ZnO阀片,其电压梯度不仅受到特高压避雷器绝缘间距、通流容量等外在因素的限制,同时也受到ZnO阀片能量吸收密度的限制。在现有生产制造能力的条件下,特高压避雷器采用ZnO阀片的电压梯度越高,阀片所必须达到的能量吸收密度也越高。笔者通过理论分析与计算得出,特高压避雷器适用ZnO阀片的方波能量吸收密度理论极限值为517 J/cm3,对应的电压梯度理论极限值为686 V/mm。对于特高压瓷套、复合外套、GIS罐式避雷器所需ZnO阀片,最理想的电压梯度分别为213、300、426 V/mm,相应的能量吸收密度要求至少分别为150、226、301 J/cm3。     

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。     

烧结温度对低压ZBCMTV压敏电阻性能的影响

采用固相反应法制备了低压ZnO-Bi2O3-Co2O3-MnCO3-TiO2-V2O5(ZBCMTV)压敏电阻,借助扫描电子显微镜、压敏电阻直流参数仪、阻抗分析仪等研究了烧结温度对压敏电阻的微结构、压敏性能和介电性能等的影响。结果表明,在较低烧结温度(980℃)下,ZBCMTV压敏电阻综合性能最好;晶粒发育比较完全,粒径大小较均一,平均粒径约13.9μm;压敏电压梯度为109.7 V/mm,漏电流密度最小为0.015μA/mm2,非线性系数最大为27.8。     

低场强高能ZnO压敏电阻的应用研究

介绍了用于电力电子装置过电压保护的低场强高能ZnO压敏电阻的组成结构,伏安特性及其等效电路,详细讨论了该保护元件的限压能力、在不同情况下的能量容量、承受脉冲负荷时的要求,最后给出了低场强高能ZnO压敏电阻在电力电子电路中的接线方法及参数选取方法。     

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。     

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。     

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.     

Structural Origin of Dimensional Effect in ZnO Varistors

The relations among breakdown field E _1mA/cm ² (electric field at 1 mA/cm²), nonlinear coefficient α (measured via current-voltage, I-V, characteristics), and change in breakdown field (ΔE _1mA/cm ²/E _{1 mA/cm} ²) (obtained via current impulse measurement), and thickness d of ZnO varistors were investigated. The dimensional effect refers to the variation in E _{1 mA/cm} ², α, and ΔE _{1 mA/cm} ²/E _{1 mA/cm} ² with thickness of the samples. The dispersion of the ZnO grain size and the aspect ratio of the ZnO grains are used in characterizing the microstructure to represent the degree of heterogeneity of the grain size distribution and irregularity of the shape of the ZnO grains. The distribution of the ZnO grain size is statistically analyzed and found that the critical thickness d _c increases linearly with the dispersion of the ZnO grain size. The breakdown electric field can be empirically termed as E _{1 mA/cm} ² ∝ exp(bd), where d is the thickness and b represents the transitional behavior for the curve of the E _{1 mA/cm} ² versus d plot. Based on the inflecting response of this curve, b ₁ represents the small thickness domain prior to the inflection and b ₂ represents the large thickness domain in the post-inflection domain. It is observed that b ₂ is directly proportional to aspect ratio of the ZnO grains. Also it is revealed from the analysis that b ₁ increases with the increase in the critical electric field while b ₂ decreases with the increase in the critical electric field. Based on these observations it is suggested that the dimensional effect of ZnO varistors originates from the distribution of the grain size and proven via experiments involving the measurements of E _{1 mA/cm} ², α, and ΔE _{1 mA/cm} ²/E _{1 mA/cm} ². The dimensional effect is the macroscopic expression of population behavior of varistors that is consisting of the ZnO grains as well as the grain boundaries.     

ZnO压敏电阻组合波回路输出的仿真

为了仿真分析压敏电阻对组合波短路电流波形参数的影响规律,采用了三折线法了建立了压敏电阻的仿真物理模型,在组合波未加任何负载时,短路电流的波前时间、半峰值时间、反极性震荡以及虚拟电阻分别为7.67μs、21.59μs、12.48%和2.07Ω。加入压敏电阻负载的仿真研究得出:对于压敏电压U1mA为18V的压敏电阻负载,当储能电容上电压从200V变化到15kV时,组合波短路电流波的波前时间由7.35μs变化到7.67μs,变化率为4.35%,半峰值时间由21.16μs变化到21.66μs,变化率为2.36%;虚拟阻抗由2.48Ω变化到1.999Ω,变化率为19.40%。而对于压敏电压U1mA为330V的压敏电阻负载,当储能电容上的充电电压从1000V变化到15kV时,组合波8/20μs短路电流波的波前时间由5.79μs变化到7.5625μs,变化率为30.6%,组合波8/20μs短路电流波的半峰值时间由18.1μs变化到21.43μs,变化率为18.4%,虚拟阻抗由6.434Ω变化到2.16Ω,变化率达66.4%。研究结果对压敏电阻的特性研究和组合波电路的设计提供了理论依据。     

ZnO的双脉冲电流冲击老化破坏试验

研制了一个双脉冲电流冲击试验装置 ,对氧化锌非线性电阻进行在双脉冲电流作用下的老化破坏试验 ,分别考察了电阻的老化破坏特性与冲击次数 n、双脉冲间隔时间 Δt的关系 ,指出在双脉冲电流冲击下 ,电阻更易发生击穿破坏     

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.     

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.     

Mechanical Activation of Spinel and Pyrochlore Phases in ZnO Based Varistors

Mixtures of ZnO, Sb₂O₃ and Bi₂O₃ powders corresponding to the stoichiometric compositions of Zn₇Sb₂O₁₂ (spinel) and Zn₂Bi₃Sb₃O₁₄ (pyrochlore) were milled in a shaker mill (SPEX) up to 180 minutes. The influence of the mechanical activation of the powders, as a result of the milling, was determined by Differential Thermal Analysis, Thermogravimetric Analysis and X-ray Diffraction. Additionally, in order to compare to commercial recipes the mixture ZnO + 2.7 wt% Sb₂O₃ + 4.5 wt% Bi₂O₃ was milled in a shaker mill up to 180 minutes. Varistor devices were fabricated with both milled and unmilled mixtures. The devices were characterized by I-V studies, Scanning Electron Microscopy and X-ray Diffraction. Mechanical activation on the system ZnO-Bi₂O₃-Sb₂O₃ produced a chemical reaction and amorphization in the powder mixture. The weight loss due to volatilization of Bi₂O₃ and Sb₂O₃ that occurrs in both ZnO-Sb₂O₃ and ZnO-Sb₂O₃-Bi₂O₃ systems at temperatures below 1200C is reduced by milling the powder mixtures.     

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。