Accelerated ageing of medium voltage cold shrink joint materials under combined stresses

Cold shrink joints are widely used on the Medium Voltage French distribution network. The high reliability of these joints is particularly important to control the shortage duration of the energy supplied to customers. Two outer protection materials of cold shrink joints were subjected to combined stresses of temperature, humidity and stretching/unstretching. The experimental ageing protocol favoured the application of realistic stresses, lower than those generally applied in acelerated ageing studies, but over a longer test duration. The outer protections were characterised throughout the ageing. After one year of ageing, the materials showed superficial oxidation, which was lower in liquid water than in other relative humidity conditions. On complete joints, subjected to the HD629-3 robustness test protocol, breakdown voltages are stable over three consecutive test sequences.