OCR Text |
Show I Reason Buried Cables Heat I RITISH electrical engineers bavo ba try- JjO ing to find a way to lessen the tendency of buried cables to deteriorate through heating ,fj and through the same cause to suffer a los in conductivity. At a recent conference in Llver- X pool experts reporting the results of various 4 tests showed that paper-covered wires, unlike ; I those Insulated in rubber gutta percha. were J 1 subject to considerable variations in longitu- I dlnal expansion. A rise from the "normal"' ! i earth temperature of 60 degrees F. to 120 de- 1 I frees in a 220-yard strand of armored copper w , cablo caused an expansion of 4 inches, dls- I I tortlng the inelastic lead covering and occa- & sioning much trouble. Over 120 degree? the ! 'M dielectric loss rose rapidly or in other words, R the efficiency of the insulating medium decreases I a proportionally to the increase In heat Many 1 1 factors, it was pointed out, favored the rise in 1 the temperature of the copper conductor and i f I lessoned its eurren-carrylng capacity, such as J (9 a considerable increase in voltage, a very dry ;1 1 or loose toll, and particularly trapping of air In minute films between the paper coating and I ij the copper, or differing degrees of intimacy of I f l i contact between the dielectric and the conductor. |