Experience with miniature-cable terminations made from compounded materials and used under accelerated test conditions

Electrical termination is a critical issue in a large-scale accelerated-testing program with model extruded cables because economic forces dictate that the termination be low in cost and easily assembled. The termination must also be at least equal to the cable insulation in resisting the high stresses of accelerated testing. Achieving this result is difficult since the testing program included the continuous use of high overstresses: electrical field up to 350 V/mil or 13.8 kV/mm (seven times normal), frequency up to 600 Hz (ten times normal), and conductor temperature up to 90 C. Heat-shrinkable, resistive-capacitive electrical stress relief is a low-cost terminating technique because of easy assembly and flexibility with respect to cable diameters and constructions. The electrical losses in standard stress control material in normal usage produce a temperature rise of less than 1 C. However, under the unusual test conditions employed, excessive localized temperature rise was observed. These temperatures were reduced by using a specially formulated material with reduced loss. Reasonably successful terminations were obtained for XLPE and EPR cables with the modified material when the stresses were as noted above. Terminating LDPE cables at the higher stresses still poses a problem, although it is possible that a major part of the problem with this material was the high conductor temperature.