The oil filled cables are high-voltage transmission cables buried underground. This cable contains oil as a component of the electrical insulation. The oil is maintained at a positive pressure with respect to atmosphere, either at high pressure in pipe-type cables or at low pressure in self-contained cables, to maintain the integrity of the cable dielectric. Both types of cables are fitted with oil reservoirs to accommodate changes in load and temperature. Oil-filled cable has a number of important advantages like it prevents voids from occurring in the insulation thereby maintaining the integrity of the electrical characteristics; the steep operating potential gradient adds to the safety of operation in limited space; high voltage and high power capacity provide maximum transmission economy and oil-filled cable systems lend themselves to self-monitoring.