Complex Examination of a Cable Terminal Failure

The medium voltage cable networks act important role in electric energy distribution. The most important part of cable lines are the cable joints and terminals from the point of view of failures. In the present case study breakdown of a cable terminal appeared repeatedly in a medium voltage distribution board. The possible reasons were: penetration of atmospheric overvoltage from the connected medium voltage distribution line, assembling inaccuracy, appearance of partial discharges by not properly building-up the distribution board or lack of fitting of the termination and the cable. All of the reasons were examined: data from relays and lightning detection system, fitting of termination in laboratory and the arrangement of distribution board were analysed. Stresses in service were simulated in the laboratory. The results and the methods of examination are discussed.