Destruction of Underground Cables by Gases Generated at High Voltages Under Investigation at Engineering School

The problem presented by the injurious effects of ionized gases on the insulation of high voltage underground cables is of such importance that several manufacturers of these cables, and power companies as well, are supporting financially an investigation of it at the Engineering School, it was disclosed yesterday by R. F. Clifford, dean of the school.

In high-voltage cables, the insulation consists of paper tapes wound around the copper conductor, and impregnated with some heavy insulating oil: the whole is enclosed in a lead sheath. During the process of manufacture, air is inevitably occluded within the insulation and later while the cable is in operation gases are evolved from the oil. With high operating voltages these gases become ionized, and, striking the paper tapes, in time destroy them, literally by bombardment. In addition the heat generated chars the insulation and disintegrates the oils so that the combined effects have made high voltage cables the most unreliable link in the present electric power system No adequate test has yet been developed which will predict whether a cable will operate for any reasonable time.

The Engineering School is attacking the problem first by determining the laws of the gases and of the insulation individually, then by applying the results to the study of actual cables.

The school has developed an electrical bridge with which measurements of the high voltage involved in destruction by ionized gases may be made accurately. This bridge is used as a standard by other high-voltage laboratories, and has been duplicated by several of them.