Modelling the Impact of Ground Planes on Aircraft Transmission Cable Impedance

With the recent movement in the aircraft industry to have a more electric based secondary power system, new challenges are being uncovered, particularly with the electrical wiring interconnect system. These systems and their insulation are expected to be exposed to significantly higher voltage and frequency stresses. Complicating matters, aircraft power transmission cables are often unshielded, yet are located in close proximity to a ground plane due to the aircraft metallic structure. Electromagnetic interactions between the two in this environment are poorly understood, particularly with respect to how the cable impedance changes for higher frequency signals. Using finite element analysis (FEA), this paper investigates how field stress conditions for high frequency components change as the cable-ground distance changes. A wider discussion of the impact of the mapped behavior on future aircraft electrical wiring design and airframe integration will also be presented. Findings demonstrate that despite cable-ground plane distance being within the standard limits, the cable characteristics can still significantly change, with a 3 cm distance leading to a 15% change in impedance.