Investigation On The Aging Characteristics Of Aviation Cable Insulation

Aircraft cables are used in aircraft as transmission and distribution cable or signal wire. Aged cable insulation is prone to damage and then cause accidents. Reasonable assessment of the aging state of the cable insulation in order to determine the damage of the cable is a key issue to ensure the safety of aviation. It is essential to study the variation law of insulation performance before the establishment of an effective evaluation system for the aging state of aviation cable, and which is based on a large number of experiments. The main content of this paper is to study the aging mechanism of aviation cable insulation and the change of insulation performance under the conditions of accelerated thermal aging and damp heat aging.Aviation cable insulation material, which belongs to the high polymer, is stable due to stable structure and high molecular weight. Aviation cable faces the harsh working environment including high temperature near engine, high humidity nearly saturated, and continued strong vibration, so it needs to consider the aging factors such as heat, water and mechanics. Due to the low voltage level, the electrical aging in the aviation system is not obvious, but the study shows that the electrical aging can not be ignored. High temperature triggers the polymer degradation, water makes the polymer hydrolysis reaction happen, the vibration will enlarge micro pores caused by degradation. The results of aging is fracture of molecular chain and changes of crystallinity from microcosmic perspective, and changes of dielectric constant or insulation defect from a macro perspective.In this paper, the electric field distribution of the aviation cable is simulated and analyzed, and the equivalent capacitance of the aviation cable is calculated. The aging effect of water on insulation was investigated by the field strength distribution of the cable. Compared with the dry air, the water in the insulation is more serious and more easily to form water branch and other defects, and the existence of electric power is combined to make the insulation deterioration. The relationship between the dielectric constant and the equivalent capacitance is calculated. The change of the equivalent capacitance is mainly caused by the change of the dielectric constant, and the increase of the dielectric constant directly leads to the increase of the equivalent capacitance.The accelerated aging test was designed and implemented. Accelerated aging experiments mainly consider the temperature and humidity as aging factors. Temperature above the normal operating temperature is chosen as the aging environment temperature. Constant damp heat environment is chosen as the damp aging environment. The characteristic parameters such as the insulation resistance, dielectric constant and mechanical properties of the aviation cable are measured after aging.The results of accelerated aging test are analyzed. The direct current resistance of the aging before and after aging has no obvious change law, and the absorption ratio and the polarization index have the trend of decline. After comparing the different aging models, the elongation at break is selected as the characteristic parameter of aging. By the combination of the elongation at break and the second order reaction model, the thermal aging life equation of the aviation cable is obtained.There is an intrinsic relationship between the change of the insulation equivalent capacitance and the elongation at break, they shows a linear relationship.