Cables Multi-core

The influence of skin effects in a multi-core cable is almost the same as that of a multiphase busbar system, discussed in Sections 28.7 and 28.8. However, unlike a busbar system, the resistance and inductive reactance for various sizes of cables can be easily measured and are provided by leading manufacturers as standard practice in their technical data sheets. To this extent, making an assessment of skin effects in cables is easy compared to a busbar system. Since all the phases in a cable, of a 3-core or 3 72-core are in a regularly twisted formation throughout the length of the cable, they represent the case of an ideal phase transposition (Section 28.8.4(3)) and almost nullify the effect of proximity. 

The method of guidanoe is line of sight command, and the corrections are transmitted thru a multi-core cable fed out from the missile. The missile has two solid proplnt motors, the front annular motor being a booster. The rear motor controls the missile thru two jetavator nozzles at the rear which swivel according to the commands transmitted thru the wire. Four plastic fins provide for roll stabilization... 

The cables connecting each applicable item in the loop along with their identification numbers and, for multi core cables, pair number/identification... 

Cables provide a highly reliable and compact method of transmitting power from its sonrce to its consnmer. Cables are installed in open air on racks or ladders, in the ground, or underwater as in the case of submarine cables. Power at all the voltages normally encountered in the oil industry i.e., less than 100 V and up to 33 kV, can be transmitted efficiently by single and multi-core cables. 

An inner sheath, usually made of extruded polymer, is used to cover the insulation screen, and to fill in the interstices between the cores of a multi-core cable. It is important to fill the interstitial spaces for two reasons. Firstly to ensure good circularity and dimensional accuracy of the finished cable, and secondly to prevent an internal passage within the cable along which flammable gases could travel. The transmission of such gases along a cable must be eliminated by design and construction for cables that are used in hazardous areas. 

Multi-core cables used for control, instmmentation, compnters and telecommunications carry very small currents in their conductors, when compared with power cables, and these currents feed into very sensitive electronic circuits. The system design of these electronic circuits must take account of interference that can be induced or circulated in the cable condnctors. Screens are provided around groups of typically two, three or four conductors, which are mainly intended to discharge static charges that can otherwise accnmulate and create noise or damage at the terminal equipment. Screens are also provided aronnd all the conductors in the cable for a similar reason. 

Instrumentation cables used for power system signal transmission are usually of two basic types, multi-core twisted pairs, triples and quadruples, and coaxial cables. 

FIGURE 5.30 Refractive index ( ) profiles of optical fiber cables (a) multi-core step index fiber (b) multi-step index fiber (c) graded index fiber. (After Knisley, J. 2002. Fiber optic lighting dries out, ecmweb.com/mag/... 

When a multi-core cable of n wires, or a rope of n fibres, replaces a cylindrical rod with the same cross-sectional area (Fig. C.2c and d), each wire has diameter d = Dl n, so has a second moment of area... 

The multi-core cable used for wiring extension socket outlets should be of a type intended for use with telephone circuits, which will normally be between 0.4 and 0.68 mm in cross-section. Telephone cable conductors are identified in Table 14.10 and the individual terminals in Table 14.11. The conductors should be connected as shown in Fig. 14.62. 

In the early 1980s, a multitude of patents and patent applications were registered in the field of coextrusion of multi-layer pipes. Meanwhile, a number of pipe products representing a composite of several layers are established products on the market. The technology of the coextruded foam core pipe builds on these developments. The foam core type of PVC plastic pipe today takes the largest volume share of all coextruded foam core products. This product has developed into an important and very competitive alternative for non-pressure applications such as drain pipes, sewer pipes and cable ducts. France has played the role of a pacesetter in this development. Today, over 80% of all pipes for non-pressure applications are produced in the form of foam core pipes in that country. Since the common market realised within the EU is connected with a strong market equalisation tendency, other European countries are following. 

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