Optimization of segregation distances between harnesses for aeronautical applications

Abstract

Segregation rules are one of the three solutions to overcome EMC problems together with filtering of disturbances at the equipment inputs and shielding of cable links (braiding, covering, over-braiding, etc.). These rules enable mass reduction in the selection of cables and optimal route definition in which compatible cables (having similar levels of susceptibility and emissivity) can be installed inside the same bundles or nearby bundles, in the aircraft. The main parameters influencing the design of these "routes" are the distance that separate the routes from each other and the distance from the electrical structure, in order to avoid the effects of friction, electrical arcing (in the event of damage the insulators) and electromagnetic (EM) stresses [1]. Compatibility to environmental constraints [2] is usually obtained by the installation of filters or EM shields. Internal EMC constraints between the "routes" are solved by the application of a minimum distance ensuring that EM coupling constraints will not exceed equipment susceptibility thresholds. We suggest that, to the first order, this minimum distance is determined by modeling a pair of routes of similar length, adjusting and optimizing the segregation distance between them as shown in Figure 1. In this problem, this distance will vary mainly with the nature of the routes (EM sensitive versus EM not-sensitive) but also with the distance of each "route" from the nearest electrical reference, the coupling length and the crossing angle between two routes (as the routes can travel in parallel or cross each other with an angle). Figure 1. Principle for determining the minimum distance between two "routes" Two questions result from this approach: • How to determine this minimum distance considering the large number of configurations that are required? • If it is not possible to respect this minimum distance in the real aircraft installation, what level confidence can we give to lower distances in order to have their installation accepted? The second question is motivated by a significant number of requests for exemption from the cable design teams who have to deal with modifications of the 3D model of the aircraft and from the installation teams who cannot install the harnesses as specified, generally for mechanical reasons. To this extend, we propose to generate segregation distance tables when designing these routes to assess the level of acceptance of exemption distances.