Tracking Over Insulating Surfaces In Aerospace Environments

As aircraft move to using higher voltages, there is an increased risk of electrical failure if clearance and creepage distances of electrical apparatus, especially printed circuit boards (PCBs) are not appropriately maintained. However, conservatism can lead to dimensions being artificially enlarged leading to significant penalties in terms of weight / volume. One failure mode that can exist on insulation of PCBs is electrical tracking across surfaces, particularly those that are contaminated (this mode of failure being distinct to arc tracking in cables). This can eventually lead to electrical failure in the form of a short circuit and could pose a fire risk in some systems. For precise dimensioning of insulation within equipment, it is necessary to understand the mechanisms of electrical tracking as influenced by different environmental conditions. Work has attempted to link the variation of pressure in an aerospace environment with the process of tracking across surfaces contaminated with an aqueous pollutant. This has been done through theoretical analysis and experimental test including the development of new test techniques that can be used in a low pressure environment. Factors such as the ambient temperature and conductivity of contaminant have also been considered as part of analysis. The work has demonstrated the difficulty that would exist in preventing tracking on insulating surfaces through defining appropriate creepage distances and suggests alternative design measures would be best used to ensure tracking cannot take place.