Experience with an on-line monitoring system for 400 kV XLPE cables

The use of high voltage cables is today recommended and sometimes mandatory in order to avoid environmental concerns of the public, especially when the power system crosses areas of dense population. The reunion of the former GDR with the Federal Republic of Germany has stimulated the interest in this settlement especially for the city of Berlin, where the increase of energy demand requires the use of innovative solutions. The paper reports the activities that BEWAG, the electrical utility of Berlin, performs in order to investigate the feasibility of setting up an urban bulk power connection using 400 kV XLPE cables. During a first accelerated voltage endurance test (at CESI in Milan/Italy) on cables and accessories of six major European manufacturers several failures in joints and SF₆ terminations were encountered. Therefore the cable links for the actual second testing period were additionally equipped with partial discharge sensors for an insulation monitoring system. Sensors of this type will in the future be integrated into the cable accessories to improve after laying quality control. It is thought that this partial discharge test will replace high voltage DC-tests which were found unsuitable for the 400 kV XLPE cable technology