Harlan F. Stone

“ He described 'high tension cables for 3,000 volts' having paper insulation impregnated 'with a rather thin liquid, oily and not too resinous mass' with cable joints bound with linen tape first boiled in oil so that it is completely saturated, with the wrapped joint inclosed in a lead sleeve, soldered to the lead sheath of the cable. Through a hole cut in the top of the sleeve or socket 'hot insulating mass is poured into the socket. ”

“ Also high-tension currents, ranging upwards from 15,000 volts, develop heat in the conductors and adjacent material, with consequent expansion and corresponding contraction when cooling, known as 'breathing.' This causes migration of the in sulating compound within the cable and to some extent its extrusion, and produces cracks and voids in it, with resulting ionization of the interstitial air at high tensions, and the lowering of the dielectric strength or resistance of the cable at the joint. ”

“ This sleeve, he stated, was then filled with an insulating compound of either 'an oil or a viscous joint box compound, preferably the latter, which can run into the tubes and all parts of the joint box.' Again, 'Such a compound must be viscous of about the consistency of thick cream at ordinary temperatures. When heated it should run as freely as heated oil so as to penetrate all crevices and it must retain these features through its life. ”

“ The potheads used as oil reservoirs in the Baltimore installation, when full of a free-flowing oil, were observed to overflow when the cables were heated, and the migration of the oil along the cables for considerable distances was also noted. ”

“ To avoid the draining out of the cables and the consequent defective insulation in sections extending vertically from the subterranean conduits to the power houses, the cables were passed into enlarged containers or potheads containing oil, which, flowing downward in the cables, replenished the oil in the jute insulation for distances as great as 1,200 feet. ”