Three-phase single-core cable system with core-redundancy
University of Duisburg-Essen
Energy-Transport and -Storage
Planning new extension routes for the power grid reinforcement leads directly to the question:
“overhead line or underground cable?”. Amongst all the considered technical and ecological
weighing ups, the economical comparison is mostly the decisive factor . While, for thermal
reasons, the cable has a considerably greater conductor than the overhead line and therefore
noticeably lower loss costs, the overhead line normally causes lower investment costs even in
rural areas. One decisive advantage of a cable route, however, is its better acceptance by the
citizens and, by this, better prospects of a fast realization. As a consequence the approval
procedures for cables within 1-2 years are usually substantially faster than these of overhead
lines. Furthermore interferences to nature and scenery as well as the expenditures for their
compensation are reduced considerably.
Regarding the reliability aspects of supply, the so called (n-1)-redundancy, realised in the
cable route, is often demanded by the utility. This means a twin system for the overhead line,
which, however, is useful in many cases concerning the loss costs . The destruction of
power poles, for example during the gale-force storms in France in 1999, leads to a loss of the
redundancy of the overhead line twin system though.
When undergrounding cables, often two parallel systems are laid into the trench side by side.
For the transmission of great power, the single core cables will not be arranged bundled but in
a flat formation (as in fig. 1b). In order to suppress sheath- or screen-losses by circulating
currents, a cross-bonding of the sheaths/screens is carried out.
The broken line in fig. 1b suggests to provide an additional fourth core instead of a complete
second system. Such a suggestion is alrea