Heat Transfer Challenges for MVDC Power Cables Used in Wide Body All Electric Aircraft Under Low Pressures

Abstract

Power cables are a vital component of the future electric power systems (EPS) envisaged in wide body all electric aircraft (AEA). They are required to be high power delivery and low system mass. Designing proper power cables for AEA faces thermal challenges due to the lower pressure of 18.8 kPa at the cruising height of a wide body aircraft. Due to the limited heat transfer at that pressure, the temperature field distribution across the aircraft cable, mainly a function of pressure, surface emissivity, and ambient surface geometry, is likely to diverge from that at atmospheric pressure. Moreover, temperature field distribution affects the conductivity of the insulation, which in turn alters and may inverse the electric field distribution across the DC cables. Therefore, a coupled multi-physics study should be conducted to calculate the temperature field and electric field across the cable at different ambient temperatures and various possible geometries of the ambient environment. In this paper, the temperature field distribution across a 5 kV DC cable is studied at atmospheric and 18.8 kPa pressures. The voltage level of 5 kV was resulted from our previous studies where we proposed new EPS architectures for a wide-body AEA. The main purpose of this study is to obtain the maximum permissible current flowing the cable at the atmospheric and 18.8 kPa pressures regarding the thermal limits of the cable. It is shown that at 18.8 kPa the maximum permissible current flowing the cable is decreased by 14.75% compared to its value at atmospheric pressure when the size of the ambient surface is 250 mm. Also, the electric conductivity and electric field across the cable insulation are evaluated at different conductor currents and insulator temperature gradients.