The effects of pressure and temperature on partial discharge degradation of silicone conformai coatings

Abstract

The partial discharge damage rates for silicone-coated printed circuit boards have been quantified in a series of experiments at pressures and temperatures relevant to the aerospace industry (down to 116 mbar, -55°C to +70°C) and up to 6 kV. Surface cracking was observed, and damage magnitude was found to be non-linear with coating thickness, with thinner coatings experiencing relatively greater damage rates. This is attributed to higher surface electric fields for a given energisation voltage. Increasing temperature or reducing pressure increased the rate of damage. For coating thicknesses less than 100 µm, reducing pressure to 116 mbar (1 mbar = 100 Pa) increased the relative crack growth rate by nearly an order of magnitude. Temperature change had the most profound influence on damage; low temperatures were observed to substantially reduce damage rate, with very little or no damage observed, whereas higher temperatures substantially increased damage rate, with the resulting magnitude of surface damage too large to quantify. Silicone coatings of thickness greater than 250 µm showed no appreciable damage from partial discharge when aged at either low pressure or high temperature at voltages up to 6 kV. Corresponding damage-free surface electric fields are computed. No samples were observed to fail, indicating the robustness of high quality silicone coatings. Possible causes of crack formation in silicone are discussed.

Discussion on Electric Power Supply Systems for All Electric Aircraft

“…However, due to the wiring praxis in electrical aircraft electrical field enhancements can be the consequence and lead to PD [152], [153]. Furthermore, high operating temperatures due to high distribution currents could lead to a faster aging of the cables and have to be tested in PD-tests before the cable design is selected [149], [154], [155]. Solutions to eliminate PDs could be developed in future research projects, like the use of screened cables [156] and new insulation materials which provide better PD resistance sheathes [157].…”

Effects of Environmental Factors on Partial Discharge Activity and Estimation of Insulation Lifetime in Electrical Machines

“…At low pressures, enhanced PD activity is likely due to the reduced relative air density. The decrease in the relative air density increases the electron mean free path (λ) as given in (8) and (9) [17], [22].…”

“…Consequently, the electrons gain more energy and generate electric discharges by crossing more distance between two collisions. Secondly, an increase in the equilibrium temperature of the insulation material reduces the additional energy required from bombarding electrons [17]. Therefore, the discharges are more active and harmful at high temperatures resulting in the faster degradation of the insulation material.…”

“…Based on the results of R-square goodness of fit hypothesis, the plausibility of two terms Gaussian model was established. The results of two term Gaussian model are given in (17), (18) and (19). This article has been accepted for publication in a future issue of this journal, but has not been fully edited.…”

“…The effect of humidity and temperature on PD measurements in stator winding was presented in [15], [16]. The impact of high temperature on PD activity and the insulation degradation was studied in [17]- [19]. The correlation between discharge magnitude and the temperature was presented in [20], [21].…”