Industrial Research 



325 



their qualities, and their arrangement; and the character 

 of the protective sheaths for the cables and materials 

 available therefor. Many manufacturers of cables, and 

 power companies which are users of cables, have carried 

 on such research. Some of this has not been of exactin<; 

 scientific character, but much of it has been, and con- 

 tinues to be, higlily commendable for its scientific 

 character and the resiUts produced. 



As elsewhere in industrial research relating to elec- 

 trical engineering, men of a variety of learning and skills 

 have been needed for, and have participated in, cable 

 research. On account of the materials to be used and 

 their structural associations, the researches have called 

 on chemists, physicists, metallurgists, mathematicians, 

 and engineers. The problems to bo attacked are atomic 

 and molecular, electrical, physical (in the sense of struc- 

 tural), and chemical (in the sense of general and organic 

 chemistry). Efforts are directed to discovering im- 

 proved selection and arrangements of materials, to the 

 improvement of cables of known types, and to the 

 reduction of costs of manufactiu-e, so that users may 

 secure cables of higher voltage ranges, greater reliability, 

 and longer life, and withal secure cables of the needed 

 qualities at lower prices. 



Cables may be made up with one conductor within a 

 protective sheath or with several conductors within a 

 common sheath, and may be used for a tliree-phase 

 circuit, for example, with three single-conductor cables 

 or with one three-conductor cable. Copper of high 

 electrical conductivity is the approved material for the 

 conductors of insulated cables, but the form of the cross- 

 section of the conductor has some significance. How- 

 ever, the major problems of high-voltage cables relate 

 to the insulation and its protection. Cables compe- 

 tent to transmit power of moderately high voltage (say 

 66,000 volts) came into some use early in the decade of 

 1920-30, and thereafter their use was extended rapidly. 

 Cables for commercial power transmission have now 

 been produced for voltages as high as 220,000 volts; 

 but the problem of full reliability in service is still in 

 the domain of research. 



The materials now most used commercially or experi- 

 mentally for high-voltage cable msulation are oil-im- 

 pregnated paper of specific quality, rubber compounds, 

 synthetic rubber substitutes, varnished cambric, free-oil 

 and gas filling, the last two being associated with suita- 

 ble separators for the conductors and with suitable 

 supply tanks, and sometimes with means for main- 

 taining a relatively high pressure in the tanks. Rubber 

 compounds and synthetic rubber substitutes are usually 

 confined to low-voltage conductors, as also are insu- 

 lating coverings composed of asbestos, glass fabrics, and 

 certain plastics. 



The problems of heat conductivity, heat dissipation, 

 and the safe temperatures for various insulating mate- 



rials make disturbing relations as also do corona effects 

 in unhomogeneous arrangements. The producers of 

 refined petroleum oils and the manufacturers of certain 

 resins and other chemical compounds have actively 

 joined in the researches relating to the applicabilitj' of 

 their products to cable and wire insulation. 



Among the outcomes of research in this field are 

 improvements in the methods of measuring the quali- 

 ties of insulating materials and of cable insulations, and 

 also in methods of periodically testing cables in situ 

 to discover whether they are deteriorating. The latter, 

 of course, is a preventive against deterioration being 

 allowed to go to the point of insulation break-down and 

 consequent interruption of the electric service at some 

 moment of inconvenience for the power users, since the 

 tests will show whether a cable should be replaced. 



Protective sheaths composed of lead have long been 

 a subject of concern because of their mechanical frailty 

 and in certain circumstances their readiness for cor- 

 rosion or fatigue. Research has not found a substitute 

 but has pointed the way to eliminate some of the 

 causes of weakness of lead sheaths and shows promise 

 of discovering some improved lead alloy, or alloys, 

 which may serve the purpose more satisfactorily. 



Wliile the great problems of electrical conductor insu- 

 lation relate to the higher voltages used in power trans- 

 mission, the annual expenditure in this country for 

 insulated conductors to be used for low-voltage circuits 

 on consumers' premises has led to active research by 

 some companies in the effort to find more favorable 

 compounds for the substance of such insulation ma- 

 terials. Considerable progress has been made of recent 

 years, but apparently more may be accomplished. 



Miscellaneous Applications 



Innumerable commercial applications of electricity 

 have been improved by the results of research which 

 have not been referred to La the foregoing, just as innu- 

 merable details have not been mentioned specifically, 

 although such details are within the fields discussed 

 where industrial research has served importantly. For 

 examples there are numerous household conveniences 

 such as electric refrigerators, air-conditioning devices, 

 and the like, which are tlie outcome of extended 

 research. 



Space does not warrant discussing these various 

 features, but one special application commands men- 

 tion, namely, electric welding. Wlien Elihu Thomson 

 introduced the resistance-welding process and de 

 Meritens introduced the arc-welding process, these at 

 first received relatively scant attention except for places 

 where complete assurance of the integrity of a weld was 

 not of primaiy importance. However, in later years, X- 

 ray and corresponding methods of examining completed 

 welds have been proved to be practicable and electric 



