120-Kv compression-type cable

THE oil-filled type of high-voltage paper-insulated cable has been used on all extra high-voltage underground installations now in service in this country. While the major portion of these installations operates at oil pressures under 30 pounds per square inch, several of the shorter ones utilize oil pressures up to 200 pounds per square inch (“oilostatic” type). Although an alternate system¹ in which a high gas pressure is applied externally to the lead sheath has been in commercial service abroad since 1932, it was not until recently that this type of cable, known as compression cable, received serious study here. In 1939 the Detroit Edison Company found that a system employing a welded steel pipe line offered a number of advantages over the conventional duct installation under the conditions existing over the route of a projected 120-kv underground circuit. For this reason the companies with which the authors are associated initiated an intensive laboratory and field investigation of the technical characteristics of several systems employing a steel pipe. The present paper describes some of the more interesting results of the technical investigation on the compression cable system.