Challenges of extruded cable for HVAC and HVDC power transmission

The paper presents the challenges of the construction of extra-long high power underground cable transmission lines. Economical approach has pushed to increase cable lengths per shipping drum; the technical obstacles to be overcome and the performances required as a result of the increase in potential stresses applied to the screen insulation are shown. Different novelties in bonding diagram such as “direct cross bonding” are explained, highlighting their benefit as well as their prerequisites and drawbacks. The use of longer shipping lengths as well as of “direct cross bonding” method supposes that an accurate and thorough study of the electrical stress applied to joint shield break is carried out as part of the basic design of the link. The authors give practical experience with direct cross bonding. The increasing use of VSC (Voltage Source Converter) Technology is encouraging the use of synthetic insulated cables and both long submarine and underground links are being considered and actively implemented. Space charge formation under d.c. stress is certainly the major concern. A successfully test qualifications according to CIGRE recommendations TB 219 and currently to TB 496 have been performed on a full cable system. The tests were conducted for a nominal voltage U= 320 kV.