Pre-breakdown arcing and electrostatic discharge in dielectrics under high DC electric field stress

2015 IEEE Conference on Electrical Insulation and Dielectric Phenomena (CEIDP)

2015

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This work provides physical insight into common statistical models for DC dielectric breakdown field strengths. Voltage step-up tests were performed on low density polyethylene films. The merits of generalizations to widely-used empirical Weibull models are discussed. The cumulative probability distributions of the breakdown fields were fit to standard two-and three-parameter Weibull distributions. Mixed two-parameter Weibull distributions, sometimes used in the literature to model multiple breakdown modes, were found to yield the best fits to the data. In addition, the same data were fit to a physically-motivated dual-defect mean field model incorporating both low-and highenergy defect modes with different defect densities; this produced a much better fit than single-defect mean field models. Values obtained for the mean defect energies and densities were within the ranges expected from independent determinations of these intrinsic materials properties. By incorporating these physicsbased concepts into traditionally empirical models, their accuracy and utility can be extended. The mixed Weibull distribution and the dual-defect model predicted very similar cumulative distributions of LDPE breakdown data, suggesting that mixed Weibull distributions may reflect similar multiple defect modes used in dual-defect models. Theories of DC breakdown, based on distributions of microscopic defects in disordered insulating materials may provide improved guidance in understanding the physical origins of empirical parameters used in statistical methods to characterize breakdown properties.

“…There are indications that there is a non-zero threshold field for breakdowns [3,6,7,9,10]. Such a threshold is incorporated in dynamic breakdown models [6,11,12].…”

Section: B Three-parameter Weibullmentioning

confidence: 99%

Mixed Weibull distribution model of DC dielectric breakdowns with dual defect modes

2015 IEEE Conference on Electrical Insulation and Dielectric Phenomena (CEIDP)

2015

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“…Increases in current significantly steeper than the ohmic curve do not make sense in terms of Ohm's law (V=IR) for the circuit; these are likely due to the ammeter response to increasingly rapid pre-arcs-so rapid that return to baseline current may not be observed [4,10]. Much, if not all, field enhanced conductivity (which is relatively infrequent in MPG tests) will be below the 10% curve; further, field enhance conductivity is expected to increase supra-linearly with voltage and can therefore be distinguished from breakdown.…”

Section: Breakdown Voltage Can Be Defined As the Average Voltage Betwmentioning

confidence: 99%

An enhanced operational definition of dielectric breakdown for DC voltage step-up tests

2017 IEEE Conference on Electrical Insulation and Dielectric Phenomenon (CEIDP)

2017

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Abstract-The imprecise definition of breakdown in the ASTM D3755-14 standard can misidentify breakdown. If the recommended test circuit current sensing element threshold is set too high, breakdown may occur undetected. Conversely, false positives may result from designating a low current threshold. An operational definition of breakdown much less sensitive to these pitfalls is outlined herein. This enhanced definition of breakdown is based on the average rate of change of the leakage current with increasing voltage, rather than a simple current threshold, avoiding ambiguous association with anomalies in current traces. For tests that continuously monitor leakage current, breakdown can be detected by a transition from negligible current to an ohmic slope defined by the circuit's current limiting resistors. In practice, a fixed current threshold is inadequate to define dielectric breakdown. Field-enhanced conductivity, partial discharge, surface flashovers, incomplete breakdowns, and other phenomena may further obscure the characteristic dielectric breakdown signature. Pre-breakdown anomalies in current traces can also now be clearly identified and studied, in addition to the breakdown itself.

“…When our test system was first used, the prearcing events were dismissed as noise. Upon closer inspection, it became clear that these events are clearly above the system noise and that the pre-arcing behavior changes from material to material [4].…”

Section: B Comments On Pre-arcingmentioning

confidence: 99%

“…Several pre-arc events have been measured using a fast oscilloscope simultaneously with the ammeter (inset of Fig. 1) [4]. The arcs observed with the oscilloscope had widths of ≲5 μs (this may have been limited by the RC time constant of the measurements circuit) as compared to the ammeter's response time of ~0.5 s This demonstrated that a single large amplitude pre-arc signature in the ammeter data can actually be multiple smaller fast pre-arcs integrated over the ammeter's data response time.…”

Section: B Comments On Pre-arcingmentioning

confidence: 99%

“…Step-up to breakdown tests were performed on samples of low density polyethylene (LDPE). The breakdown events were observed together with transient, non-shorting current spikes that have been termed pre-arcing [4]. For each permanent and irreparable shorting breakdown event, many pre-arc events were observed as the applied electric field was ramped to breakdown.…”

Section: Introductionmentioning

confidence: 99%

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Pre-breakdown arcing as proxy for DC dielectric breakdown testing of polymeric insulators

2015 IEEE Conference on Electrical Insulation and Dielectric Phenomena (CEIDP)

2015

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Pre-breakdown arcing is proposed as a key indicator of DC breakdown properties of polymeric dielectric materials. Voltage step-up tests were performed for films of lowdensity polyethylene (LDPE) at ramp rates significantly lower than is common in most studies, allowing for the observation of both breakdown and transient pre-breakdown current spikes. The distributions of the breakdowns versus applied field were compared with the more frequent pre-breakdown arcs. A strong correlation was observed for LDPE between the distribution of breakdowns in step-up tests and the distribution of prebreakdown arcing. Pre-breakdown arcing distributions are much easier to obtain than breakdown distributions and may be an efficient indicator of the minimum field at which breakdown can occur, leading to accelerated test methods. The possible physical origins underlying pre-arcing and its relation to breakdown distributions are discussed.