DocumentCode :
3205191
Title :
Insulator surface flashover due to UV illumination
Author :
Javedani, J.B. ; Houck, T.L. ; Lahowe, D.A. ; Vogtlin, G.E. ; Goerz, D.A.
Author_Institution :
Lawrence Livermore Nat. Lab., Livermore, CA, USA
fYear :
2009
fDate :
June 28 2009-July 2 2009
Firstpage :
832
Lastpage :
837
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), RexoliteR 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/cm2, 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.
Keywords :
flashover; lighting; surface discharges; ultraviolet radiation effects; vacuum insulation; HDPE; Rexolite insulator; UV illumination; anode triple junction; anode-half illumination; cathode triple point; cathode-half beam illumination; charge-balance equation; excimer laser; high density polyethylene; high voltage power supply; insulator cone angle; insulator size; insulator surface flashover; photon to electron conversion; pulsed laser beam; thick angled insulators; ultraviolet radiation; vacuum chamber; vacuum insulators; Anodes; Cathodes; Dielectrics and electrical insulation; Flashover; Insulator testing; Lighting; Optical materials; Pulse measurements; Surface resistance; Voltage;
fLanguage :
English
Publisher :
ieee
Conference_Titel :
Pulsed Power Conference, 2009. PPC '09. IEEE
Conference_Location :
Washington, DC
Print_ISBN :
978-1-4244-4064-1
Electronic_ISBN :
978-1-4244-4065-8
Type :
conf
DOI :
10.1109/PPC.2009.5386369
Filename :
5386369
Link To Document :
بازگشت