Power cable

7 Examples of high-voltage design 6.7.1 Power cables 

To prevent unacceptably high contact voltages [1,2], metal sheathing of power cables in transformer and switching stations and in the distribution network is connected to grounded installations, which have a low grounding resistance. This increases the danger of corrosion and makes corrosion protection more difficult if  

Although the above listed series of operations appear simple in outline there is an immense amount of knowhow in the accurate control of the process. Especially important is the maintenance of concentricity and the minimizing of longitudinal shrinkage during the final heat-shrinking procedure. The extrusion, irradiation and deformation steps are disparate in capacity, and mainly for this reason are not run in tandem. 

This study is particularly concerned with the application of heat-shrinkable plastics materials to power-cable terminations. Some of the principle types of cable involved are briefly described below. 

This type of cable comprises conducting cores insulated with paper or plastics insulation or dielectric. Around the outside is a lead or nowadays more commonly aluminium sheath with finally an outer armour. This is the type of cable which provides the normal house or office service. The house service version has one phase and one neutral core, but in the distribution box the incoming cable will contain four or five cores. 

There are two essentially different types of high-voltage cable one has a plastics dielectric, the other a paper dielectric. 

Which of these two principal types is the better is not clear-cut. The plastics insulation is relatively easy to apply by cross-head extrusion. PVC, polyethylene, crosslinked polyethylene, ethylene propylene rubbers are commonly used. This is a relatively cheap and efficient process. Paper cable manufacture, by comparison, is a complex and labour-intensive 

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H = Hydraulic Hoses P = Power Cables S = Signal Cables... 

Power cables Power cycles Power factor Powerforming... 

Each segment of the insulated wire and cable industry has its own set of standards, some of which are quite compHcated because of requirements imposed by specific appHcations and/or environments. The most complex specifications are typically imposed on power cables and telecommunication wires. 

Typical power factors for an EPR-based compound employed for 5—35 kV power cable is approximately 0.03—0.05% when measured at room temperature and about 1.0—1.4% measured at 90°C. 

Generally, trees occur under the relatively high voltages associated with power cables (11—13). Trees can be classified in three classes electrical, water, and electrochemical. 

Tests on Cable Constructions. The Association of Edison Illumination Companies (AEIC) has approved an accelerated cable hfe test in which typical underground distribution power cables can be statistically compared based on their resistance to water treeing (number of days to fail). The comparison can be made by varying the type of insulation and/or other cable layers in an environment that contains hot water (90°C) under 8V/fi (200 V/mil) voltage stresses (four times the typical power cables operating voltages). 

Power Gables. The materials mostly used to produce power cables are ethylene copolymers loaded with conductive carbon black for ... 

Table 4. Components Used in Power Cable Insulations Based on EPR, Parts by Weight ...

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

Kerite Co., Distribution Cable and Power Cables data catalogues, Seymour, Conn. 

Union Carbide Corp., Kabelitems Wire and Cables No. 157, A. Critical Comparison ofXEPE andEPR for use as Electrical Insulation on Underground Power Cables, Danbury, Conn. 

Lead—copper alloys are the primary material used in the continuous extmsion of cable coverings for the electrical power cable industry in the United States. Other alloys, containing tin and arsenic as well as copper, have also been developed for cable sheathing in the United States to provide higher fatigue strength. 

Number of power cables running together and their configuration. For more details refer to Chapter 16, Appendix 1. The cooling of the cables is affected by the number of cables and their formation. This detail... 

Consider an average derating of 67% for power cables when operating at an ambient temperature of 50°C. 

Consider an average derating of 0.8 for a number of power cables bunched together, generally not more than six at a lime. 

The heat generated by a current-caiTying component or conductor is its watt loss and is expressed by R, where / is the current and R the resistance of the circuit under consideration. The watt loss of each current-carrying component installed in the test assembly is estimated and added to arrive at the approximate watt loss during the actual operation. Based on this loss is calculated of the total heaters required. These heaters are then suitably located in the test assembly to represent all the incoming and outgoing feeders, their power cables and any other current-carrying component. 

Power connections and control wiring The loss within such components is measured by their resistance, which, in the case of cables, is a function of their size and length. The loss in the external power cables is calculated similarly, parts of which run inside the assembly to connect the various feeders, by measuring their average length inside the assembly. 

Total kiss in power cables Total watt losses A + B + C... 

Appendix 1 Selection of Power cables 16/531 A 16.1 Introduction 16/531 A16.2 Technical details 16/544 A16.3 Service conditions 16/544 A 16.4 Recommended derating factors 16/544 A 16.5 Voltage drop 16/544... 

To provide a reference for those working on power projects or at sites, we provide some important data on different types of LT and HT power cables in this appendix. The cables described here are in use for all kinds of power distribution applications. Of these, XLPE cables are also used for power transmission applictiiions. To help a user to select the most appropriate types of cables, we also provide a brief comparative chart of the various types of cables being manufactured. Tables giving the technical particulars of such cables in all voltage ratings have also been provided. 

The selection process of power cables is almost the same as that of a bus system discussed in Section 28.3. For simplicity we consider only the basic data for selection which would suffice the majority of applications. For accurate calculations a similar approach will be essential as for the bus systems (Chapter 28). For site conditions and laying arrangements which may influence the basic rating of a cable, corresponding derating factors have also been provided. The information covered here will be useful to users to meet their cable requirements, although the data may vary marginally for different manufacturers. For more data on cables, not covered here, reference may be made to the cable manufacturers. 

Table A16.3 LT cables Armoured twin and multicore power cables 650/1100 V...

Table A16.5 HT Cables up to 11 kV Armoured three-core power cables 1.9/3.3 kV ...

Table A16.6 Armoured three-core power cable 3.8/6.6 kV (grounded system)...

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 -... 

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