Classification of Cables w.r.t Insulation

Classification of Cables w.r.t Insulation Points : Classification of Cables w.r.t Insulation The construction of cable is that to envelope the conductor a non-conducting material. The insulation is this material in which the electricity can’t flow. For cable insulation there are only insulation material are used such as. P.V.C, mica power, Fiber etc. The purpose of insulation is that to provide protection electric chock, leakage of current and fire etc. 1. Vulcanized rubber insulated cables Natural rubber is the coagulated latex of certain” species trees. Vulcanized rubber is posse’s high insulating qualities, be the material absorbs moisture and deteriorates by rapidly oxidization into a resinous substance. Therefore to 5 percent amount sulphur is incorporated with the rubber as a result, it becomes impervious to water, flexible and of high resistivity. This whole process is known as vulcanized and the product .which it obtained is known as vulcanized rubber. This process is performed at 149°c which is above the melting point of sulphur. It has a good mechanical strength, dependent upon its degree of vulcanization When we using this type of cable in which place, where the heat and day light are not present, and the vulcanized rubber retain’s physical properties for a long period. 2. T.R.S or C.T.S Cables Tough rubber sheath(T.R.S) protection, first introduced by the St Helens Cable co.., under the name C.T.S (cab tyre sheath) is usually laped on to the already insulated conductor In tough rubber sheathed cable,. The conductor is insulated with vulcanized rubber insulation. TR.S-cables are manufactured in this way that the cables are with stand the mechanical damage. A hard rubber cover is used to protect the cable from external damage effects. In this type of cables hard rubber or thermo plastic cover is used on single or two core or three core V.R.I cables. This type of cable is commonly used in open wiring system. The external sheath cover provides the, mechanical protection not for electrical insulation to the cables. The diameter of sheath cover is 1/2 cm approximately. 3. Impregnated paper insulation cables Due to increasing cost of rubber, another form of insulations introduced. After many experiments a conductor insulted 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 on to the desired thickness to achieve a required dielectric strength. The copper conductors, lapped with layers of paper impregnated with a good instating compound. The impregnated paper consist of a felted matt of long fibers. Washing of the both at the pulps stage and after formation of the she 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 for cable insulation. But today, the chemical wood-pulp paper-wood sulphate is generally used. The paper insulation is laid on to the conductors and then being vacuum dried. After drying the insulation it is impregnated under pressure with mineral oil or 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 has 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 filled sealing. It is essential that the paper which is impregnated must 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 me is depending upon the type of cable. 4. P.V.C cables P.V.C is the most usual insulant because of its good general performance and economic advantage P.V.C was developed as cables insulation in 1930. It is obtained from two gases, such as acetylene and hydrogen chloride. When these two gases react, as a result, vinyl chloride is obtained and then vinyl chloride is polymerized to produce polyvinyl chloride which is a white color powder with a high softening pomp, showing very little tendency to flow under heat and pressure. Before using this material as cable insulation it must be incorporated with certain material know as plasticizers Plasticizer is a liquid which has high boiling point and their function is to Seen the basic material and make it flexible. By adjust of the amount of plasticizer the mechanical properties of the pvc can be varied over a wide range. 5. Varnished cambric insulated cables The cambric efficiently dried and treated with suitable insulating varnish with a liberal surface coating has been used to an increasing extent. After treatment the varnished surface is dried hard. No this surface becomes a flexible and smooth. The varnished cambric insulation is prepared to dip the cotton into varnish. Varnished, is prepared by oil and petroleum jelly rall together. After preparing the, varnished cambric sheet, a multiple layers of varnish is applied the conductor in the form of tape. If require, the cable is also lead-covered and braid and finally suitably compounded. We know that the moisture is fatted on the cable; therefore the outer cover of petroleum jelly is laid on the insulation. 6. Poly-Chloro-Prene cables The P.C.P is a rubber like material. The insulation has a resistant against highly corrosive form products and also weathering. Danger is arises when we use these cables with mineral acids and alkalis. P.C.P cable work at 55°c. Ozone, which is formed by the action of the sunlight, ultra-violet rays, attacks exposed natural rubber whilst P.C.P cable are unaffected by this action. 7. lead sheath cables This is a V.R.I cable and sheathed with a lead alloy. This cable is manufactured in one two and three cores design with in the lead sheath. The lead sheath cover protected the cable against mechanical shocks. This cable is commonly used for moisture places because the lead has a resistant against moisture. Oil impregnated paper is inherently hygroscopic and it is therefore necessary to ap1y a moisture resisting sheath over the insulated cores. This sheath may he composed of metallic or non-metallic materials the former being usual1eád or an alloy of lead. Lead and lead alloy’s have until recent years been the most convenient materials for sheathing power cables, because of their case and high speed of application. 8. Armoured cables When cables are not insulated in conduit or trunking then they may require armour for that purpose a galvanized steel wire helically applied around a cable and such cables are known as armoured cables. Armoured P.V.C and XPLE (cross linked polyethylene insulated cables are now being used extensively for main and sub-main cables in wiring system. The armoured cable is consists of multi core P.V.C insulated cables, with P.V.C sheath and Wire armour4 Another P..V.C sheath is covered the overall cable. The armoured cable is much lighter and easier for handle. A steel tape is wounded on the cable. This steel tape protect the cable against mechanical shocks. If armou1ng is done by using a steel wire, then P.V.C sheath is laiped on the steel wire.