NDLI: Insulator surface flashover due to UV illumination

Content Provider	IEEE Xplore Digital Library
Author	Javedani, J.B. Houck, T.L. Lahowe, D.A. Vogtlin, G.E. Goerz, D.A.
Copyright Year	2009
Description	Author affiliation: Lawrence Livermore National Laboratory, L-154, 7000 East Avenue, CA, USA (Javedani, J.B.; Houck, T.L.; Lahowe, D.A.; Vogtlin, G.E.; Goerz, D.A.)
Abstract	The surface of an insulator under vacuum and under electrical charge will flashover when illuminated by a critical dose of ultra-violet (UV) radiation - depending on the insulator size and material, insulator cone angle, the applied voltage and insulator shot-history. A testbed comprised of an excimer laser (KrF, 248 nm, ∼16 MW, 30 ns FWHM,), a vacuum chamber, and a negative polarity dc high voltage power supply (≤ −60 kV) were assembled to test 1.0 cm thick angled insulators for surface-flashover. Several candidate insulator materials, e.g. High Density Polyethylene (HDPE), $Rexolite^{R}$ 1400, $Macor^{™}$ and Mycalex, of varying cone angles were tested against UV illumination. Commercial energy meters were used to measure the UV fluence of the pulsed laser beam. In-house designed and fabricated capacitive probes (D-dots, ≫12 GHz bandwidth) were embedded in the anode electrode underneath the insulator to determine the time of UV arrival and time of flashover. Of the tested insulators, the +45 degree Rexolite insulator showed more resistance to UV for surface flashover; at UV fluence level of less than13 $mJ/cm^{2},$ it was not possible to induce a flashover for up to −60 kV of DC potential across the insulator's surface. The probes also permitted the electrical charge on the insulator before and after flashover to be inferred. Photon to electron conversion efficiency for the surface of Rexolite insulator was determined from charge-balance equation. In order to understand the physical mechanism leading to flashover, we further experimented with the +45 degree Rexolite insulator by masking portions of the UV beam to illuminate only a section of the insulator surface; 1) the half nearest the cathode and subsequently, 2) the half nearest the anode. The critical UV fluence and time to flashover were measured and the results in each case were then compared with the base case of full-beam illumination. It was discovered that the time for the insulator to flash was earlier in time for the cathode-half beam illumination case than the anode-half illumination case which led us to believe that the flashover mechanism for the UV illumination is initiated from the cathode side of the insulator. Qualitatively stated, the testing revealed that the shielding of the cathode triple point against UV is more important than the anode triple junction in the design of vacuum insulators and electrodes.
Starting Page	832
Ending Page	837
File Size	1458950
Page Count	6
File Format	PDF
ISBN	9781424440641
DOI	10.1109/PPC.2009.5386369
Language	English
Publisher	Institute of Electrical and Electronics Engineers, Inc. (IEEE)
Publisher Date	2009-06-28
Publisher Place	USA
Access Restriction	Subscribed
Rights Holder	Institute of Electrical and Electronics Engineers, Inc. (IEEE)
Subject Keyword	Flashover Lighting Dielectrics and electrical insulation Insulator testing Anodes Surface resistance Cathodes Optical materials Voltage Pulse measurements
Content Type	Text
Resource Type	Article

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