Impregnated Paper Insulation Electric Cables

Impregnated paper insulation electric cables 

Due to increasing cost of rubber, another form of insulation is introduced. After many experiments a conductor insulated with paper or jute were introduced. The paper or jute being impregnated with a suitable compound, The paper insulation is laid on to the conductors in the form of paper taps, which is laid helically to the desired thickness to achieve a required dielectric strength. The copper conductors, lapped with layers of paper impregnated with a good insulating compound. The impregnated paper consist of felted matt of long fibers. Washing  of the both at the pulps stage and after formation of the sheet fibers, is an important. Because due to this factor the properties of the paper for cables can be controlled.
At one time manila was recognized as the best paper cable insulation. But today, the chemical wood-pulp sulphate is generally used. The paper insulation is laid on to the conductors and then being vacuum dried. After drying the other suitable compound. A two-core cable, the insulated cores of a cable is laid up together with a packing of jute or paper to give a circular formation. If the cable lras three, four or more cores, each core is prepared separately and generally laid up with an overall layer of paper. All cables ends are sealed by special compound muct be free from moisture. For this purpose the conductors or cores are placing in a heated chamber that can be reduced to a vacuum. The value  of temperature and heating time is depending upon the type of cable.
This drying process is followed by impregnation of the cable with suitable insulating oil or compound. In these cables, if greater mechanical protection is to be provided, the steel armoring is usually applied over a over a bed of jute or layer of tape. The purpose of the metallic shielding tape around a cable is to control the electro static stress and decrease the thermal resistance of cable. A sheath of lead provides the necessary protection. A sheath of bitumen compound has been used successfully. Although vulcanized bitumen has the advantage of being light and flexible, after laid on paper insulation on conductor, a cotton of potson contained red led compound core is also laid on the cable.
The disadvantage of impregnated paper insulation cable i that whenever joints are made to other cables an efficient sealing i essential.