Vacuum surface flashover: A high-pressure phenomenon

Gray, Eoin W.

doi:10.1063/1.335698

Cited by 69 publications

(15 citation statements)

References 41 publications

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“…Surface flashover of insulators in vacuum is generally the limiting factor in the design of high voltage vacuum devices. The most widely-accepted theory of surface flashover holds that --an avalanche of secondary electrons occurs along the insulator surface, desorbing gas through which the breakdown occurs [4][5][6][7]. The HGI overcomes the flashover by inhibiting the breakdown process using closely-spaced, floating conductors, encapsulated in a dielectric.…”

Section: High-gradient Insulatormentioning

confidence: 99%

Engineering Prototype for a Compact Medical Dielectric Wall Accelerator

Zografos¹,

Hening²,

Joshkin³

et al. 2011

AIP Conference Proceedings

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Section: High-gradient Insulatormentioning

confidence: 99%

Engineering Prototype for a Compact Medical Dielectric Wall Accelerator

Zografos¹,

Hening²,

Joshkin³

et al. 2011

AIP Conference Proceedings

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“…In SEEA charging, 6,8,13,34 the surface charge density can be expressed by: where σ is the positive surface charge; E ⊥ is the electric field perpendicular to the sample surface; and ε 0 is the permittivity of free space.…”

Section: Simulation Modelmentioning

confidence: 99%

Enhanced flashover strength in polyethylene nanodielectrics by secondary electron emission modification

Wang

Min

2016

AIP Advances

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This work studies the correlation between secondary electron emission (SEE) characteristics and impulse surface flashover in polyethylene nanodielectrics both theoretically and experimentally, and illustrates the enhancement of flashover voltage in low-density polyethylene (LDPE) through incorporating Al2O3 nanoparticles. SEE characteristics play key roles in surface charging and gas desorption during surface flashover. This work demonstrates that the presence of Al2O3 nanoparticles decreases the SEE coefficient of LDPE and enhances the impact energy at the equilibrium state of surface charging. These changes can be explained by the increase of surface roughness and of surface ionization energy, and the strong interaction between nanoparticles and the polymer dielectric matrix. The surface charge and flashover voltage are calculated according to the secondary electron emission avalanche (SEEA) model, which reveals that the positive surface charges are reduced near the cathode triple point, while the presence of more nanoparticles in high loading samples enhances the gas desorption. Consequently, the surface flashover performance of LDPE/Al2O3 nanodielectrics is improved.

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“…The limited literature search [14][15][16][17][18][19] indicated that surface flashover in vacuum seems to be triggered by charge injection into the dielectric at the triple points at the ends of the insulator. Surface composition and condition also affect flashover.…”

Section: Basis For Scale Model Testingmentioning

confidence: 99%

Impulse Flashover Tests at Edgar Beauchamp High Voltage Test Facility, Dixon, California, in Support of Cutler Insulator Failure Investigation

Hansen¹,

Dann²

2006

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EXECUTIVE SUMMARYThe Naval Radio Transmitting Station, Cutler, Maine, has experienced four insulator failures in the last decade. All are believed to be the result of lightning strikes to the antenna. The insulators that failed are fiberglass-belted safety core insulators that had been installed in the late 1990s. An investigation into these failures was undertaken in order to understand the cause of the failure and the implications to other sites having the same type of insulator. At the same time, the Navy has initiated a procurement program to replace the safety core insulators at Cutler with fail-safe insulators. The first array insulators will be replaced in the summer of 2007 and the second in the summer of 2009. The cost of this replacement is significant.The safety core insulators were tested at VLF voltage prior to their installation at Cutler, but they were not tested with impulses. All flashovers in the VLF tests occurred in the air between the corona rings. As a part of the investigation, impulse tests were done at Hydro Quebec; the tests showed that flashover occurred along the surface of the insulator when the voltage rises very fast (high dV/dt). Flashover along the surface is believed to be the primary cause of damage to the safety core insulators. Our conjecture is that making the design such that the flashover takes place in the air will protect the insulator.We used a scale model insulator to investigate the flashover phenomenon using an impulse generator owned by the Navy. The objective was to see if different corona ring configurations could keep flashover away from the insulator body. The IG was successfully activated and generated impulses up to 1.2 MV with peak times as short as 0.6 µs and up to 20-kAmp peak currents. The glaze on a small safety core insulator was melted at these current levels. Flashovers along the surface initiated from the region around the triple point at the ground end of the insulator body when that area was not well shielded. One tentative conclusion is that symmetrical grading is required on both ends of the insulator to protect the insulator body from high dV/dt impulses.The scale model tests were performed with several corona ring configurations, including the unsymmetrical one installed at Cutler. These tests showed that the flashover path can be kept away from the insulator body by bringing corona rings closer together, although this reduces the VLF withstand voltage of the insulator. Symmetrical corona ring configurations with spacing up to 2/3 of the total insulator length always flashed in the air. Non-symmetrical configurations having the small (Cutler) corona ring at the ground end flashed along the insulator surface at high values of dV/dt. The surface flashovers seemed to initiate from the triple point at the ground end of the insulator body and terminated on the high-voltage end corona ring when that triple point was well shielded.A limited set of configurations was tested. The test results were promising, indicating these insulators can be protected f...

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Vacuum surface flashover: A high-pressure phenomenon

Cited by 69 publications

References 41 publications

Engineering Prototype for a Compact Medical Dielectric Wall Accelerator

Engineering Prototype for a Compact Medical Dielectric Wall Accelerator

Enhanced flashover strength in polyethylene nanodielectrics by secondary electron emission modification

Impulse Flashover Tests at Edgar Beauchamp High Voltage Test Facility, Dixon, California, in Support of Cutler Insulator Failure Investigation

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