Thermo-mechanical characteristics of XLPE HV cable insulation

Tests were carried out on 9 metre lengths of cable in a simulated buried installation. Three XLPE insulated, lead sheathed cables were used: (1) 275 kV 630 mm² copper conductor, (2) 275 kV 1200 mm ² segmental copper conductor, (3) 132 kV 1750 mm² milliken copper conductor. Each cable was placed straight in a steel trough and backfilled with sand to simulate soil pressure at 1 m. The cable ends were firmly anchored and supported to prevent buckling and any movement as is shown. Instrumentation was installed to measure conductor forces and temperatures. The cable was heated by means of current circulation in both conductor and sheath to achieve a conductor temperature transient similar to the buried case. Each cable was heated to a nominal conductor temperature of 90°C over 8 hours and then allowed to cool overnight. This process was repeated until the peak thrust remained constant from cycle to cycle. The cable was then subjected to overload conditions, i.e. a single cycle to a temperature of 105°C, and then cycled at 90°C again until stability of peak thrust was achieved. Varied between 42 to 71 N/mm?