Cables cross-linked polyethylene

Improved heat resistance is the most important advantage of cross-linked polyethylene (XITK) over thermoplastic polyethylene. A power cable... 

NEMA WC7/1991 (ICEA 5-66-524) Cross linked polyethylene insulated wire and cable for the transmission and distribution of electrical energy ... 

Vulcanised (cross-linked) polyethylene is being used for cable application where service temperatures up to 90°C are encountered. Typical cross-linking agents for this purpose are peroxides such as dicumyl peroxide. The use of such agents is significantly cheaper than irradiation processes for the cross-linking of the polymer. An alternative process involves the use of vinyl silanes (see Section 10.9). 

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. 

The cross-linked polyethylene retains shape upto 140°C and is used for cable insulation. Polyethylene is the most widely used plastic due to its low cost and ease of processing. 

Cross-linkable polymers used for wire and cable insulations are polyolefins, certain fluoropolymers, and elastomers. Among these, radiation cross-linked polyethylene is the most widely used. The radiation cross-linking process of PE has also been the most widely studied. ... 

Insulation, Cross-linked polyethylene (XPLE) and ethylene—propylene mbber (EPR), both thermosets, are the primary extruded dielectrics used in medium and high voltage power cables (Table 4). 

Chrysler MS 8288 Cable Primary, Thin wall cross-linked polyethylene insulated, Chrysler Corporation Engineering Standard No. MS-8288, 2004. 

Figure 8.10 PD intensities and tan S values versus test voltage for a cross-linked polyethylene insulated cable (according to [30]).

Cross-linked polyethylene may include impurities and voids from which the major causes of premature failures (SCG in pipes, treeing in electric cables, and cracking in medical implants) can originate. Thus, nondestructive evaluation with effective techniques that can discover defects at the incipient stage, before the component is put in operation, is of vital importance. Conventional ultrasound (up to 10 MHz), which is the current technique for detection of flaws in metal piping and vessels, is limited by the attenuated nature of polymers. A scanning acoustic microscope with operating frequencies up to 100-150 MHz has been found to be more effective. 

The thermoset elastomers most frequently used for cables are ethylene propylene rubber and cross-linked polyethylene. 

BS5468 Cross-linked polyethylene insulation of electric cables. 

BS6622 Specification for cables with extruded cross-linked polyethylene or ethylene propylene rubber insulation for rated voltages from 3.8/6.6 kV up to 19/33 kV. 

Cross-linking polyethylene enhances its heat resistance (in terms of resistance to melt flow) since the network persists even about the crystalline melting point of the uncross-linked material. Cross-Knked polyethylene thus finds application in the cable industry as a dielectric and as a sheathing material. Three main approaches used for cross-linking polyethylene are (1) radiation cross-linking, (2) peroxide cross-linking, and (3) vinyl silane cross-linking. 

Goto T. Material recycling of silane cross-linked polyethylene insulated cable using supercritical alcohol. Electrical Insulation News in Asia [trade journal— Institute of Electrical Engineers of Japan] October 2006. 

LLDPE and HDPE use higher-molecular-weight phenols and higher eoneentrations. Cross-linked polyethylene, containing carbon black, permits use of thiodiphenols and diaryl amines, since their discoloration is masked by the carbon black. For wire and cable, hydrazides and triazines are common metal deactivators to protect against copper catalysis of oxidation. 

Table 13.8 Evaluation of kaolin in cross-linked polyethylene typically used in medium voltage cable [15],...

Flexible plastic foams may be found in the form of very soft cushioning materials used in upholstery, clothing interlayers, automobile seats, vibration absorbers, etc. The most common flexible foam resins are polyurethanes, foamed vinyls, cellular polyethylene, cross-linked polyethylene, and silicone foam. Semirigid foams are used for floatation devices, marine bumpers, special electrical insulation on television cables, packaging, and a host of other applications. Rigid foams are used in the production of airplane parts, boats, electronic encapsulation, and many furniture applications where wood was formerly used. 

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