Micro-Degradation Characteristics and Mechanism of ZnO Varistors under Multi-Pulse Lightning Strike

In view of the problem that ZnO varistors are often subjected to thermal breakdown and deterioration due to lightning strikes in low-voltage power distribution systems, this article used a 8/20 µs multi-pulse surge current with a pulse time interval of 50 ms to perform shock experiments on ZnO varistors. SEM scanning electron microscope and an XRD diffractometer were used to analyze the structure of the grain boundary layer and the change of the crystalline phase material of ZnO varistor under the action of a multi-pulse current. The damage mechanism of ZnO varistor under the multi-pulse current was studied at the micro level. The results show that the average impact life of different types of ZnO varistor is significantly different. It was found that the types of trace elements and grain size in the grain boundary layer will affect the ability of ZnO varistor to withstand multi-pulse current. As the number of impulses increases, the grain structure of the ZnO varistor continues to degenerate. The unevenness of internal ion migration and the nonuniformity of the micro-grain boundary layer cause the local energy density to be too large and cause the local temperature rise to be too high, which eventually causes the internal grain boundary to melt through, and the local high temperature may cause the Bi element in the ZnO varistor to change in different crystal phases.

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Microstructure and Electrical Properties of Low-Voltage Barium Titanate Doped Zinc Oxide Varistor Ceramics

International Journal of Recent Technology and Engineering - 2 ◽

10.35940/ijrte.d7326.118419 ◽

2019 ◽

Vol 8 (4) ◽

pp. 2713-2718

Keyword(s):

Zinc Oxide ◽

Electrical Properties ◽

Barium Titanate ◽

Grain Boundary ◽

Barrier Height ◽

Current Density ◽

Low Voltage ◽

X Ray ◽

Highly Nonlinear ◽

Zno Varistors

In the present, varistor ceramics through the combination of zinc oxide (ZnO) with a perovskite material have become widespread because of their unique properties for a wide range of applications in electronic protection devices. Low-voltage zinc oxide (ZnO) varistors with fast response and highly nonlinear electrical properties for overvoltage protection in an integrated circuit are increasingly significant in the application of low-voltage electronics. The present study highlights the interaction between barium titanate (BaTiO3 ) and ZnO varistors through the employment of solid-state reaction method in the production of low-voltage varistors. The effects of BaTiO3 on the microstructure of ZnO varistors were analyzed through scanning electron microscopy (SEM), energy dispersive X-ray analysis spectroscopy (EDS) and X-ray diffraction (XRD). The EDS analysis and XRD measurements suggest the presence of ZnO and BaTiO3 phases. The electrical properties of BaTiO3 -doped ZnO varistors were examined based on the current density-electric field (J-E) characteristics measurement. The varistor properties showed the nonlinear coefficient (α) from 1.8 to 4.8 with the barrier height (φB) ranged from 0.70 to 0.88 eV. The used of BaTiO3 additive in ZnO varistors produced varistor voltages of 4.7 to 14.1 V/mm with the voltage per grain boundary (Vgb) was measured in the ranges 0.03 to 0.05 V. The lowest leakage current density was 348 µA/cm2 , obtained at the samples containing 12 wt.% BaTiO3 with high barrier height. The reduction in barrier height with increasing BaTiO3 content was associated with the excessive amount of BaTiO3 phase, hence cause the deterioration of active grain boundary due to the variation of oxygen (O) vacancies in the grain boundary.

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Effects of Thermal Annealing for Barium and Silicon-Added Bismuth Based Zinc Oxide Varistors on Electrical Properties and Grain Boundary Structure

Key Engineering Materials ◽

10.4028/www.scientific.net/kem.582.218 ◽

2013 ◽

Vol 582 ◽

pp. 218-221

Author(s):

Atsuko Kubota ◽

Yuuki Sato ◽

Shinzo Yoshikado

Keyword(s):

Electrical Properties ◽

Grain Boundary ◽

Thermal Annealing ◽

Boundary Structure ◽

Zno Varistor ◽

Electrical Degradation ◽

Grain Boundary Structure ◽

Zno Varistors ◽

Short Time ◽

Zinc Oxide Varistors

In order to fabricate varistors with low varistor voltage, the effects of thermal annealing of CoMnBaSi-added Bi based ZnO varistors on electrical properties and the grain boundary structure were investigated. The varistor voltage for the BiCoMnBaSi-added ZnO varistor decreased in half by thermal annealing for a short time. The resistance to electrical degradation was most improved by the addition of SiO2and thermal annealing for 1020 min. It is suggested that the composition of Bi and Si in the sheet-like deposit is changed by varying the annealing time and the resistance to electrical degradation is improved by both addition of SiO2as well as thermal annealing for short time.

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Microwave Sintering of ZnO Varistor Ceramics

MRS Proceedings ◽

10.1557/proc-269-311 ◽

1992 ◽

Vol 269 ◽

Cited By ~ 1

Author(s):

Lionel M. Levinson ◽

Holly A. Comanzo ◽

William N. Schultz

Keyword(s):

Grain Boundary ◽

Microwave Sintering ◽

Boundary Effects ◽

Electrical Behavior ◽

Careful Evaluation ◽

Electronic Ceramics ◽

Zno Varistor ◽

Conventional Sintering ◽

Systematic Shift ◽

Zno Varistors

ABSTRACTZnO varistors are electronic ceramics whose electrical behavior is dominated by grain boundary effects. A careful evaluation of the effect of microwave sintering compared to conventional sintering revealed no significant differences between varistor devices processed by these two methods. A slight apparent enhancement of grain growth was observed for microwave processing, but further evaluation of this effect leads us to believe that it arises from a small systematic shift in temperature derived from the different experimental configurations.

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Optimal Phase Load Balancing in Low Voltage Distribution Networks Using a Smart Meter Data-Based Algorithm

10.20944/preprints202002.0314.v1 ◽

2020 ◽

Author(s):

Gheorghe Grigoras ◽

Bogdan-Constantin Neagu ◽

Mihai Gavrilas ◽

Ion Tristiu ◽

Constantin Bulac

Keyword(s):

Load Balancing ◽

Distribution Systems ◽

Energy Savings ◽

Low Voltage ◽

Distribution Networks ◽

Hybrid Structure ◽

Optimal Operation ◽

Time Interval ◽

Voltage Distribution ◽

Load Balancing Algorithm

In the electric distribution systems, the “Smart Grid” concept is implemented to encourage energy savings and integration of the innovative technologies, helping the Distribution Network Operators (DNOs) in choosing the investment plans which to lead the optimal operation of the networks and increasing the energy efficiency. In this context, a new phase load balancing algorithm was proposed to be implemented in the low voltage distribution networks with hybrid structures of the consumption points (switchable and non-switchable consumers). It can work in both operation modes (on-line and off-line), uploading information from different databases of the DNO which contain: the consumers’ characteristics, the real loads of the consumers integrated into the Smart Metering System (SMS), and the typical load profiles for the consumers non-integrated in the SMS. The algorithm was tested in a real network, having a hybrid structure of the consumption points, on a time interval by 24 hours. The obtained results were analyzed and compared with other algorithms from the heuristic (Minimum Count of Loads Adjustment algorithm) and the metaheuristic (Particle Swarm Optimization and Genetic Algorithms) categories. The best performances were provided by the proposed algorithm, such that the unbalance coefficient resulted in the smallest value (1.0017). The phase load balancing led to the following technical effects: decreasing the average current in the neutral conductor with 94% and for the energy losses with 61.75 %, and increasing the minimum value of the phase voltage at the farthest pillar with the 7.14 %, compared to the unbalanced case.

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SEM analysis of DC magnetron sputtered beryllium films

Proceedings, annual meeting, Electron Microscopy Society of America ◽

10.1017/s0424820100106867 ◽

1988 ◽

Vol 46 ◽

pp. 960-961

Author(s):

E. F. Lindsey ◽

C. W. Price ◽

E. L. Pierce ◽

E. J. Hsieh

Keyword(s):

Fine Structure ◽

Electron Emission ◽

Secondary Electron ◽

Low Voltage ◽

Ion Beam ◽

Secondary Electron Emission ◽

Sem Analysis ◽

Fused Silica ◽

Grain Structure ◽

Silica Substrate

Columnar structures produced by DC magnetron sputtering can be altered by using RF biased sputtering or by exposing the film to nitrogen pulses during sputtering, and these techniques are being evaluated to refine the grain structure in sputtered beryllium films deposited on fused silica substrates. Beryllium is brittle, and fractures in sputtered beryllium films tend to be intergranular; therefore, a convenient technique to analyze grain structure in these films is to fracture the coated specimens and examine them in an SEM. However, fine structure in sputtered deposits is difficult to image in an SEM, and both the low density and the low secondary electron emission coefficient of beryllium seriously compound this problem. Secondary electron emission can be improved by coating beryllium with Au or Au-Pd, and coating also was required to overcome severe charging of the fused silica substrate even at low voltage. The coating structure can obliterate much of the fine structure in beryllium films, but reasonable results were obtained by using the high-resolution capability of an Hitachi S-800 SEM and either ion-beam coating with Au-Pd or carbon coating by thermal evaporation.

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Microchemistry of ZnO Varistors

Proceedings, annual meeting, Electron Microscopy Society of America ◽

10.1017/s0424820100133102 ◽

1992 ◽

Vol 50 (2) ◽

pp. 1694-1695

Author(s):

K. K. Soni ◽

J. Hwang ◽

V. P. Dravid ◽

T. O. Mason ◽

R. Levi-Setti

Keyword(s):

Grain Boundaries ◽

Multiple Roles ◽

Grain Boundary Engineering ◽

Ion Microprobe ◽

Dopant Distribution ◽

Important Ingredient ◽

Zno Varistor ◽

Zno Varistors ◽

Zno Powder ◽

The University

ZnO varistors are made by mixing semiconducting ZnO powder with powders of other metal oxides e.g. Bi2O3, Sb2O3, CoO, MnO2, NiO, Cr2O3, SiO2 etc., followed by conventional pressing and sintering. The non-linear I-V characteristics of ZnO varistors result from the unique properties that the grain boundaries acquire as a result of dopant distribution. Each dopant plays important and sometimes multiple roles in improving the properties. However, the chemical nature of interfaces in this material is formidable mainly because often trace amounts of dopants are involved. A knowledge of the interface microchemistry is an essential component in the ‘grain boundary engineering’ of materials. The most important ingredient in this varistor is Bi2O3 which envelopes the ZnO grains and imparts high resistance to the grain boundaries. The solubility of Bi in ZnO is very small but has not been experimentally determined as a function of temperature.In this study, the dopant distribution in a commercial ZnO varistor was characterized by a scanning ion microprobe (SIM) developed at The University of Chicago (UC) which offers adequate sensitivity and spatial resolution.

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Relationships Between Grain Boundary Structure and Material Properties

Proceedings, annual meeting, Electron Microscopy Society of America ◽

10.1017/s1431927600001550 ◽

1980 ◽

Vol 38 ◽

pp. 366-369

Author(s):

Brian Ralph ◽

Barlow Claire ◽

Nicola Ecob

Keyword(s):

Grain Boundary ◽

Material Properties ◽

Main Property ◽

Grain Structure ◽

Boundary Structure ◽

Grain Boundary Structure ◽

Property Changes

This brief review seeks to summarize some of the main property changes which may be induced by altering the grain structure of materials. Where appropriate an interpretation is given of these changes in terms of current theories of grain boundary structure, and some examples from current studies are presented at the end of this paper.

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