Laser ablation of polymeric composites

Abstract

Degradation of polymeric insulation due to surface electrical discharge activity will become a more serious issue, as these materials find more widespread use. In order to improve their resistance to degradation, tests need to be performed under controlled conditions in order to rank different materials. Whilst electrical discharge activity can be simulated in the laboratory this is difficult to localize and characterize. An alternative is to use a laser to impart a known amount of energy at a known rate to a sample surface. In this investigation, the resistance of various material formulations to laser induced surface damage was tested and the materials ranked. The results are discussed in terms of the material composition and final application.

Comparison of laser ablation and inclined plane tracking tests as a means to rank materials for outdoor HV insulators

“…Whilst the observed surface damage arising from both experimental techniques is attributed to localized heating and degradation of the composite (in one case through the application of infrared radiation and in the other due to an electrical arc) [4,8], the similarities end there. Crucially the two methodologies are quite different in terms of the time dependence of the local power applied to the surface.…”

“…The hole depths were measured on bisected holes using a magnified hand graticule (accuracy ± 0.1 mm). Whilst ablation testing was performed at 3, 15 and 28 W, the ranking of samples was identical [8] therefore for clarity only results obtained at 28 W are presented here.…”

“…Plots of hole depth against energy can be used to compare the ablation performance of various materials [8], however, for easier comparison of multiple samples it is useful to extract numerical parameters from such plots; two such parameters are the initial ablation rate R init (the ablation rate in mm/J at energy = 0) and the maximum hole depth D inf (the hole depth in mm at energy = ∞). Curves that showed linear behavior and no obvious maximum hole depth were fitted to the polynomial; 2 bx ax y   Where a and b are constants and differentiation indicates that a = R init .…”

“…A carbon dioxide laser (Synrad) operating at a wavelength of 10.5 -10.6 µm was used to irradiate the samples [6][7][8]. The power output of the laser was controlled by a PWM controller over the range 2 to 28 W. For safety, the laser was enclosed in a metal interlocked cabinet which was vented externally to remove fumes.…”

“…Inclined plane tracking tests have proved useful in evaluating the performance of a number of silicone rubber based systems [4] and indicate that materials containing a high filler loading are beneficial up to the point where a good dispersion of the filler can be maintained [5]. An alternative testing methodology is to use a laser to apply a known amount of power at a known rate to the sample surface [6][7][8]. However, in order to realistically simulate the thermal damage associated with electrical discharge events [2], an infra-red laser is required [9] and measurements of typical electrical arcs indicate that the local power density needs to be in the range of several watts to several tens of watts, with total energies up to several kJ [10].…”