Thermal Runaway in Metal Oxide Varistors

Seitz, Michelle E.; Hirthe, Richard W.; Potter, M. E.

doi:10.1557/proc-5-405

Cited by 4 publications

(1 citation statement)

References 4 publications

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“…The value of m shows an increase of 75% after the sample has been stressed for 5 hours. It is more than likely that such a device approaches thermal runaway [17][18][19] in a very short time. Eventually the device is expected to fail.…”

Section: The Degradation Of Zno Varistors Coated With Epoxy Resin Undmentioning

confidence: 99%

The Degradation of Epoxy Resin‐Coated ZnO Varistors at Elevated Temperatures and Ambient Humidity Conditions

Alim

et al. 2003

Active and Passive Electronic Components

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The degradation of the epoxy resin-coated commercial ZnO varistors at elevated temperatures and ambient humid conditions has been investigated experimentally. It has been observed that the leakage current of the ZnO varistors increases under the voltage stress at elevated temperatures with ambient humidity content. The change in the leakage current corresponding to a fixed electric field with respect to the initial current is taken as the dimensionless degradation index. This index is monitored at various experimental conditions in conjunction with the curing condition of the epoxy resin powder. The results are carefully evaluated, and it has been found that the diffusion process of the moisture into the ZnO varistors plays a key role in the degradation process provided that these varistors had excellent property to begin with. The ionisation of the moisture at the interface between the ZnO block and the epoxy resin coating leads to the increase of the leakage current. Furthermore, the role of the ambient pressure corresponding to the elevated temperatures is considered as the variable to the degradation process. These data are also monitored and analysed as a function of time.

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Section: The Degradation Of Zno Varistors Coated With Epoxy Resin Undmentioning

confidence: 99%

The Degradation of Epoxy Resin‐Coated ZnO Varistors at Elevated Temperatures and Ambient Humidity Conditions

Alim

et al. 2003

Active and Passive Electronic Components

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Data‐Handling and Analyzing Criteria

2017

Immittance Spectroscopy

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Electrical barriers in the ZnO varistor grain boundaries

Alim

Liu

et al. 2006

Physica Status Solidi (a)

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In this paper a detailed nature of the electrical potential barriers in ZnO based varistors are presented. The excellent nonlinear current–voltage (I–V) characteristic of these varistors is attributed to the potential barriers formed between the successive ZnO grains during the processing cycle. These grain boundaries in the microstructure results in a few device‐related parameters such as built‐in‐potential, barrier height, barrier width, grain carrier density, Fermi level position in the grains, etc. Thermal activation energy is determined from the status of the leakage current of this device. Substantial studies conducted to comprehend possible conduction processes in the grain boundary regions under applied bias (electric field). It is understood that electron transport dominate the grain boundary regions based on electrical potential barrier consideration across the grain boundaries. The free electrons overcome potential barrier at elevated temperatures as well as under bias. These carriers fill trap sites (charged defect states) both in the bulk ZnO and in the grain surfaces (surface states). The formation of space charge region within the successive ZnO grains across the grain boundaries is a result of the equilibrium state of the device. Based on the findings an expression of the Schottky potential barrier width is proposed satisfying relevant expression of the current caused by the application of the electric field. It is observed that the potential barrier width is sharply reduced in the temperature range 320 K ≤ T ≤ 350 K. This reduction in the potential barrier width is likely to be associated with the relaxation process of the trap filled (trapped) carriers, usually monitored by the dielectric response (in the form of differential capacitance) of the device. Thus, the results provide an improved understanding of the nonlinear conduction behavior in ZnO varistors. (© 2006 WILEY‐VCH Verlag GmbH & Co. KGaA, Weinheim)

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Thermal Runaway in Metal Oxide Varistors

Abstract: The conditions leading to thermal runaway in metal oxide varistors are discussed in terms of its power dissipation. An equivalent circuit is used to rationalize the similarities and differences between the DC and 60 Hz ac behavior.

Cited by 4 publications

References 4 publications

The Degradation of Epoxy Resin‐Coated ZnO Varistors at Elevated Temperatures and Ambient Humidity Conditions

The Degradation of Epoxy Resin‐Coated ZnO Varistors at Elevated Temperatures and Ambient Humidity Conditions

Data‐Handling and Analyzing Criteria

Electrical barriers in the ZnO varistor grain boundaries

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