A heuristic is a method used to approximate an ideal solution for a complex problem within an acceptable time frame. The heuristic approach used by the transmission system operators is referred to as a genetic algorithm. This method iteratively evaluates thousands of combinations of the possible grid enhancement and expansion measures. The genetic algorithm ensures that only the most suitable combinations are carried forward into the next iteration until the desired grid structure (expansion grid) is obtained. The iterative method is intentionally stopped once only a few instances of congestion remain and the marginal utility of additional enhancement or expansion measures is lower than the use of redispatching measures to resolve the remaining overloads.

High current cabling

In contrast to high-temperature conductors, so-called high-current cables have significantly larger cross-sections compared to standard conductors (see high-temperature conductor) and are preferred for technical and economic reasons when constructing new lines along existing or new routes. As a general rule, high-current cabling has a continuous current-carrying capacity of 3,600 or 4,000 A per circuit with a permissible conductor cable end temperature of 80°C. Due to its larger cross-section, high-current cabling results in lower levels of grid losses when transporting an identical amount of current and lower noise levels compared to standard conductors and the above-mentioned HTC lines. Since high-current cabling has investment cost advantages and operators have many years of experience working with this technology, it is generally preferred over HTC cables.

High voltage direct current transmission (HVDC)

High voltage direct current transmission (HVDC) is a process for transmitting large volumes of electrical power at very high voltages (up to 1000 kV) over very long distances. High voltage inverters are required in order to feed the electricity into the conventional AC energy grid. This conversion takes place at converter stations / converter plattforms also known as rectifiers and frequency converter stations.

High-temperature conductor (HTC, HTLS)

High-temperature conductors (HT conductors or HTC) are cables that use certain materials allowing them to operate at higher temperatures than standard aluminium or steel cables. Standard cables have a maximum permissible temperature of 80°C, whereas high-temperature conductors can reach operating temperatures of 150°C to 210°C. Due to this level of temperature resistance, HT conductors offer a greater current-carrying capacity than standard conductors with the same cross-section.

There are different types of HT conductors: TAL (thermal resistant aluminium) conductors, which are already in use, and the latest generation of conductor cables, HTLS conductors (high temperature, low sag). TAL conductors have a maximum operating temperature of 150°C, whilst HTLS conductors can operate at up to 210°C. Due to the special core material used in HTLS conductors, they sag less compared to other types of conductor cables under higher levels of load. Provided that it is technically feasible and receives regulatory approval, the recabling of routes from standard conductors to HT conductors is one option for grid expansion in accordance with the NOVA principle.

HVDC transmission line

The energy generated at offshore wind farms is transported to a point in or close to the respective offshore wind farm cluster. If a DC grid connection system is being used, the energy is then transmitted from here through an HVDC transmission line to an onshore grid connection point.