Insulation for cables

Use High-temperature coatings, laminates and composites for aerospace vehicles, ablative materials, oil sealants and retainers, adhesives, semiconductors, valve seats, bearings, insulation for cables, printed circuits, magnetic tapes (high- and low-tem-perature-resistant), flame-resistant fibers, binders in abrasive wheels. 

Washing-up bowls, baths, insulation for cables, road signs, children s toys... 

Eleetrieal properties of biodegradable polylactic acid films were measured and compared with those of erosslinked polyetlylene (XLPE) cimently used as insulation for cables and electric wire [10]. The volume resistivity, dielectric constant and dielectric loss tangent of PLLA were found to be almost the same as those of XLPE. However, the impulse breakdown strength of PLLA was 1.3 times that of XLPE. 

Another example is insulators for cable connectors which have been previously injection moulded from LR or HTV. Then, they are expanded and held in that state by a plastic spiral which is removed when it is applied onto the cable (thus retaining the original shape of the insulator). A large number of similar applications can be found in the automotive, medical fields, etc. 

Separate collection of cables is a very easy and economic source of metals and plastics. Insulators for cables are mainly made of PVC and LDPE, but rubber can be also present. A typical layout of a plant for recycling PVC insulators from cables is reported in Figs. 13 aandb [10]. 

CSM compounds possess excellent resistance to ozone attack, oxidation, and weathering, even for nonblack products. Also, these CSM compounds usually possess some oil, water, and chemical resistance. Therefore, CSM compounds are used in environmental applications (especially pond linings), insulation for cables, spark plug boots, coated fabrics, hose covers, single-ply roofing, rafts, and folding kayaks. 

Manufacturer Recommended for polymers Recommended for products Outstanding properties paints, sealants, floe insulation for cables fire retardant, low vc Orica Australia PVC, PU jring, flexible hose, )latility... 

Sulfur hexafluoride was first prepared in 1902 (1). The discovery in 1937 that its dielectric strength is much higher than that of air (2) led to its use as an insulating material for cables, capacitors (3), and transformers (4) (see Insulation,electric). Sulfur hexafluoride has been commercially available as AccuDri, SF (AUiedSignal Inc.) since 1948. It is also produced by Air Products and Chemicals in the United States and by others in Germany, Italy, Japan, and Russia. 

Fine Powder Resins. Fine powder PTFE resins are extremely sensitive to shear. They must be handled gendy to avoid shear, which prevents processing. However, fine powder is suitable for the manufacture of tubing and wire insulation for which compression molding is not suitable. A paste-extmsion process may be appHed to the fabrication of tubes with diameters from fractions of a millimeter to about a meter, walls from thicknesses of 100—400 )J.m, thin rods with up to 50-mm diameters, and cable sheathing. Calendering unsintered extmded soHd rods produces thread-sealant tape and gaskets. 

For primary insulation or cable jackets, high production rates are achieved by extmding a tube of resin with a larger internal diameter than the base wke and a thicker wall than the final insulation. The tube is then drawn down to the desked size. An operating temperature of 315—400°C is preferred, depending on holdup time. The surface roughness caused by melt fracture determines the upper limit of production rates under specific extmsion conditions (76). Corrosion-resistant metals should be used for all parts of the extmsion equipment that come in contact with the molten polymer (77). 

The cables designed for use at voltages over 49 kV require that the conductor and insulation shields be firmly bonded to the insulation in order to avoid any possibiUty of generating corona at interfaces strippable insulation shields are not accepted. The A ETC specifications for cables rated for 59—138 kV require a volume resistivity of one order of magnitude lower than for the medium voltage cables. 

R. B. Blodgett, "Ethylene—Propylene Rubber and Crosslinked Polyethylene as Insulations for 90°C Rated Medium Voltage Cables," Rubber Chem. Technol, 52, 410-424 (1978). 

Commonly used materials for cable insulation are poly(vinyl chloride) (PVC) compounds, polyamides, polyethylenes, polypropylenes, polyurethanes, and fluoropolymers. PVC compounds possess high dielectric and mechanical strength, flexibiUty, and resistance to flame, water, and abrasion. Polyethylene and polypropylene are used for high speed appHcations that require a low dielectric constant and low loss tangent. At low temperatures, these materials are stiff but bendable without breaking. They are also resistant to moisture, chemical attack, heat, and abrasion. Table 14 gives the mechanical and electrical properties of materials used for cable insulation. 

General requirements PVC insulated electric cables for voltages 3.3 kV to 11 kV ... 

Cross linked po)y elhylene insulated PVC sheathed cables Power cables w ith extruded cross-linked insulation (XLPE cables) for voltages from 1 kV-3 kV(V = 3.6 kV) 7098-1/1988 ... 

Tests for power cables with extruded insulation for rated voltages above 30 kV up to l.iO kV (XLPE cables) 7098-3/1998 -... 

The header cable between anode bed and rectifier must be particularly well insulated. For this reason cables with double plastic sheathing of type NYY-O are used. The cable sheath must not be damaged during installation because the copper core at the defects will be anodically attacked in a very short time and the connection to the rectifier broken. Damage to the cable sheath is not so serious if a multicored cable is used. Usually not all the core insulation is damaged so that the operation of the anode bed is not interrupted. In addition, measurement of resistance and detection of defects is easier. 

The excellent electrical insulation properties of polyethylene have led to extensive use in cable and other wire-covering applications. Spectacular early uses included undersea cables and airborne radar and the materials continue to be used in substantial quantities. One particular trend is the increasing use of cross-linked polyethylene for this area of use. Such materials have improved heat resistance and in addition have given generally better resistance to stress cracking. Cellular polyethylene is used as the insulator for television downlead aerials. 

During the next few years PVC was steadily developed in the United States and in Germany. Both countries were producing the material commercially before World War II. In Great Britain, ICI in 1942 and the Distillers Company in 1943 also commenced pilot-plant production of PVC, a material then in demand as a rubber substitute for cable insulation. Paste-forming grades suitable for the production of leathercloth also became available soon afterwards. 

Applications include high-performance insulation for wire and cables (particularly heater cables), and corrosion-resistant linings for pumps, valves, pipes and other chemical equipment. Its availability in the form of film and tubing has led to its demand for both corrosion protection and antistick applications. 

Table 16.7 Comparison of full-load capabilities for paper, PVC and XLPE insulated copper cable...

Examples of ASTM plastics insulation for wire and cable specifications are presented that relate to type plastic and specific field of application. 

D 2219 Vinyl Chloride Plastic Insulation for Wire Cable 60 C Operation. 

D 2308 Polyethylene Jacket for Electrical Insulated Wire Cable. 

D 2802 Ozone-Resistant Ethylene-Propylene Rubber Insulation for Wire Cable. 

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