What are different types of underground cable?
Generally, cables are mainly of two types, over head cable and underground cable. Overhead cables are not insulated and are connected with the transmission towers via different types of porcelain insulators to prevent grounding and short circuit of lines. This is the only reason why overhead transmission lines are less expensive and used more than underground cables.
Whereas underground cables are fully covered by insulation. They are classified in different types of underground cable depending upon the insulating materials used for insulation. Generally paper is most commonly used for the insulation. In general, underground cable is surrounded by paper and then impregnated with insulating compound and thereafter a metal sheath is applied.
Three phase solid paper insulation are of two types:
Belted type andShielded type.
Belted type consist of three conductors which are separately insulated. Then all the cables are insulated again with paper. Whereas in shielded type insulation, three cables are insulated and then they are kept together by a non-magnetic Armour. Typically, shielded type insulation is more preferred.
After the solid paper insulation there is another type of insulation namely oil filled insulation. Oil is filled around the cables, which act as an insulating medium. Various steps are taken to measure the oil pressure.
.
The disadvantage of this type of insulation is during contraction and expansion, there is a chance of leakage of oil which ultimately leads to fault.
Another type of insulation is gas cushioned insulation. In this technique, cables are paper insulated and covered with rubber to prevent water from entering the cable.
The pressure is maintained at about 14 kg / cm2 and a clearance of about 0.175 cm is kept for single cables. For having high insulating property and high dielectric strength, SF6 gas is used in this type of cable insulation. This insulation can provide insulation for thousands of MVA.
No comments:
Post a Comment