Many industrialized cities do not have enough space to build additional high-voltage lines to serve the electric power needs of their communities. Growing demand for electricity has increased the amount of power equipment being used to service that increased demand. In order to meet this growing demand, the service and security capabilities of electric grids and the oil-filled equipment also need to grow.
One of the ways electric power companies are meeting the increased demand for electricity in the “space constrained” industrialized cities is through the use of “Oil-Filled” cables. Oil-filled cables are bulky substitutes for high-voltage networks that are constantly visible. Oil-filled cables remain hidden from view and are laid out in trenches 3 meters deep on special fixed brackets. Essentially, the cables are placed in an underground cable pipeline that normally has a diameter of between 70 to 80 millimeters. A transmission cable consists of a copper conductor wrapped in insulating paper that is placed inside the cable pipeline. The cable is filled with insulating oil and then it is sealed.
Liquid insulation, or cable oil, is used in all oil-filled cables of 110 kV and above. As with any other type of oil used in the energy industry, the cable oil must meet certain requirements and standards. The failure to comply with the required standards and specifications will most likely result in equipment failures and can lead serious accidents.
Requirements for cable oil are actually much higher than for electric power transformer insulating oil. Cable oil therefore, is usually made from a more highly refined base oil. The oil is usually enriched with performance enhancing additives that increase resistance to oxidation. Key indicators and standards for cable oils differ depending on their classification.
The cable type of insulating oil is exposed to various contaminates that impair its properties and performance characteristics that lead to aging, degradation, and malfunction of the cable system. In order to prevent these cable system enemies from disrupting electric service, an oil cleaning system is used to purify the cable oil. It is done in a batch fashion and ultimately, the cleaning system will be used to introduce the oil under high pressure into the tank that is used to supply and service the oil-filled cable.
Most often, purification equipment for cable oil is of the dehydration type where the primary task is the removal of moisture from the oil while also performing other cleaning functions. The purification unit consists of a vacuum column (degasser), a coarse filter, two fine filters and two fore-pumps to increase the productivity of the purification process.
In one cycle, a dehydration type unit can normally process up to 800 liters (800L) of cable oil in an eight (8) hour period. After a full cycle of processing, the oil is re-directed to the pressure tanks. For the refilling process, lead tubes are used. Each pressure tank has two valves, one for removing the cable oil, and one for refilling the tank with cable oil.
The demand for cable oil cleaning equipment is quite large both in our country and throughout the entire industrialized world. Energy companies must use every opportunity to prevent accidents, breakdowns, and power outages due to contaminated liquid and solid insulation. Cable oil therefore, must be properly cleaned and maintained.
Installing new high voltage power lines in congested and industrialized cities with limited space has become increasingly impractical. The laying of underground cables however, is a reasonable solution for the ever growing demands for electricity. Cleaning equipment for cable oil has therefore, not lost its relevance. Cable oil cleaning equipment may not be as versatile as the new systems for comprehensive cleaning and regeneration of industrial oil but, it does a very good job of maintaining the purity of the cable’s solid and liquid insulation. This helps to prevent cable failures and electric service interruptions.