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Space Charge Characterization in Insulating Materials used in Aircraft Cables

The increase of on-board power in aircrafts will probably go with massive introduction of DC networks. Though voltages are much less than in power transmission cables, weight optimization implies that systems are not overdesigned. Besides, aeronautic specifications and environment stresses are more demanding. One popular cable technology uses wrapped insulation, with polyimide (PI) as inner insulation and polytetrafluoroethylene (PTFE) as outer layers, ensuring fire resistance and arc tracking resistance properties. Space charge measurements in such multilayer is more complex than in extruded cables. In order to anticipate issues with direct measurements on cables, multilayers of PI and PTFE have been investigated by pulsed electroacoustic (PEA) method. For PI, we clearly show that the fluorinated layer added onto PI to improve adhesion between rolls has a strong impact on the response. The PEA signal is influenced by the bilayer formed due to dielectric permittivity difference mainly. When associating PTFE and PI, the charge resolution within PI is further distorted due to the strong diffusivity of PTFE for acoustic waves. From the present results, difficulties forecasted for the measurement on cable materials are discussed.