High-voltage grid · Glossary

The high-voltage grid is the grid level at which electricity is transported at high voltage over regional distances and distributed to larger load and generation centres. In Germany this mainly refers to the 110-kilovolt level. In grid descriptions and in the grid-charge system it is usually called grid level 3. The transformation from high to medium voltage in substations is regarded as a separate grid level, level 4. Above it lies the extra-high-voltage level with 220 and 380 kilovolts. Below it lies the medium-voltage grid, which supplies towns, commercial areas, smaller industrial connections and local distribution substations.

The term first of all designates a voltage level. It does not automatically say anything about ownership or function. Technically, high voltage serves to transport large amounts of power with acceptable losses. For the same power, current falls as voltage rises. Ohmic line losses increase with the square of the current. If the current is halved, these losses therefore fall to about a quarter. As a result, large amounts of energy can be transmitted more efficiently over longer distances and grid losses remain limited.

For design purposes, what counts is not the kilowatt-hour but the power that can be transmitted safely. It is usually stated in megawatts or, for equipment, in megavolt-amperes. Lines, transformers and switchgear bays are rated for a certain maximum load. The amount of energy transported results only from power multiplied by time. This distinction is important: bottlenecks do not arise because too much energy is available over the year. They arise because load flows are too high at certain points in time.

Distinction from extra-high voltage and medium voltage

The high-voltage grid is often equated with the transmission grid. This is imprecise. In German practice, the transmission grid mainly comprises the 220 and 380 kilovolt level. It connects large regions, neighbouring countries, large power plant sites, offshore connections and central nodes of the power system. It is operated by the transmission system operators, who are responsible for large-scale power balancing.

Legally, the boundary is less sharp than the voltage values suggest. The Energy Industry Act (Energiewirtschaftsgesetz) defines transmission in § 3 as transport via an extra-high-voltage and high-voltage interconnected grid, including cross-border interconnectors. Distribution is defined there as transport at high, medium or low voltage via electricity distribution grids. High voltage thus appears in both definitions. Which category a grid belongs to is decided not by voltage alone, but also by function and the responsible operator.

In Germany, the 110-kilovolt grid belongs predominantly to the distribution grid and is operated by distribution system operators. It takes electricity from the extra-high-voltage level and passes it on to the medium-voltage grids via substations. At the same time, large consumers and larger generation plants are connected directly to this level. In regions with a lot of wind, in industrial areas or in areas with large solar parks, the high-voltage grid is therefore not a mere intermediate step but a heavily used operating level.

It differs from medium voltage through higher voltage, greater transport capacity, greater reach and different protection and operating concepts. The gap to the low-voltage grid is even more pronounced. Households, small businesses, individual heat pumps or charging points are not connected directly to the 110-kilovolt level. Their effect can nevertheless become visible there when many decentralised installations together change the load profile of a grid area.

Technical function in grid operation

A high-voltage grid consists of overhead lines or underground cables, substations, transformers, switchgear, protection systems, measurement systems and control technology. Transformers couple the voltage levels. Switches isolate line sections, establish other switching states or make maintenance possible. Protection systems detect short circuits and other faults. In this way the affected part of the grid can be switched off quickly without needlessly disconnecting larger areas from the grid.

In operation, it is not enough merely to check whether a line still has headroom on paper. In AC grids, load flows distribute themselves according to the electrical properties of the grid, above all the impedances, and not according to supply contracts. An electricity supply contract does not determine which physical path the power takes. Grid operators therefore monitor switching states, the voltage band, reactive power, equipment temperatures and safety reserves.

Safe operation generally includes the (n-1) criterion. If a single item of equipment fails, such as a line or a transformer, the grid should nevertheless remain stable. The usable capacity is therefore smaller than the sum of all technical maximum values. A line may appear free in normal operation and still already be limiting, because the failure of a neighbouring element would threaten an overload.

Why the high-voltage grid matters for the energy transition

For a long time the high-voltage grid was designed mainly to distribute electricity from above into the regional consumption areas. This direction can no longer be taken for granted today. Wind farms, solar parks, biomass plants, battery storage, electrolysers, data centres, large heat pumps and electrified industrial processes increasingly connect to this level. As a result, electricity more often flows from the distribution grid towards the transmission grid or between regional grid areas.

This has practical consequences. A wind farm may make economic sense at a given site, but it can feed in only if lines, substation, protection concept and voltage control cooperate. An industrial company planning an electric process plant may need not only a line but also new transformers or reinforced switchgear. A battery can relieve the grid or put additional strain on it, depending on whether it is operated according to price signals or grid signals.

Germany has its own framework for planning. Under § 14d EnWG in the currently published version, distribution system operators must submit a grid expansion plan to the regulatory authority every two years by 31 October, for the first time in 2026. This applies in principle from 100,000 connected customers. Smaller operators are also obliged if in each of the two preceding years they curtailed more than 3 percent of possible wind or solar generation. The basis is a regional scenario drawn up by the operators of a planning region with the involvement of the transmission system operators. The plan must contain grid maps of the high- and medium-voltage grid showing bottleneck regions. It must also set out optimisation, reinforcement and expansion measures for the next five and ten years as well as the need for flexibility services. The law classifies the construction and operation of distribution grids as being in the overriding public interest.

In the high-voltage grid, technical connectability, regional location policy and regulated grid charges therefore meet. Grid operators do not build freely according to market prices, but within a regulated framework. Investments must be approvable, justifiable and refinanceable. Connection requests from individual projects meet long-term grid planning, permitting procedures, long delivery times for transformers and questions of local acceptance.

Typical misunderstandings

A widespread error is to regard high-voltage grids as pure transport lines. In practice, transport is closely tied to regional distribution, voltage control and fault management. An additional line therefore does not automatically solve every problem. The bottleneck often lies in a substation, a transformer, the protection grading, a missing switching option or in the interplay of several items of equipment.

Equally imprecise is the idea that the energy transition needs only extra-high-voltage lines from north to south. Such lines are important for large-scale balancing. But many concrete connection problems arise in the 110-kilovolt grid and below. If wind or solar capacity in a region grows strongly, the electricity must first reach the next higher level or be consumed locally. If this regional absorption capacity is lacking, the result is curtailment, delayed connections or expensive interim solutions.

The underground cable is also often seen as a simple alternative to the overhead line. At the 110-kilovolt level it is indeed more widespread than in extra-high voltage, and the law promotes it. Under § 43h EnWG, new high-voltage lines up to 110 kilovolts on new routes are to be built as underground cables. This applies as long as the total costs for construction and operation amount to at most 2.75 times those of a technically comparable overhead line and nature conservation concerns do not stand in the way. At the project developer's request, the authority can nevertheless permit an overhead line if public interests do not stand in the way. A new line that runs to a very large extent in or directly next to an existing route does not count as a new route. Technically, however, a cable is not merely an overhead line laid differently. It generates considerably more capacitive reactive power, has different thermal limits and usually takes longer to repair when damaged.

Another misunderstanding concerns the term capacity. Grid capacity is not a stored amount of energy, but the ability to transmit power safely at a given point in time. When politicians or the media speak of a lack of grid capacity, it should be clear what is meant: lines, transformers, connection capacity, voltage control, redispatch, permits or operational reserves. Without this distinction, it remains open which measure would help at all.

Link to flexibility and system costs

With more weather-dependent generation, it becomes more important when and how heavily the high-voltage grid is used. A grid section may be sufficient most of the time and be heavily overloaded for a few hours. There are several solutions for this: grid expansion, more consumption locally, grid-related adjustment of feed-in, storage, controllable loads or grid-serving operation of large plants. Which solution is cheaper depends on how often, how long and how severely the load occurs.

Since 1 October 2021, grid-related interventions in generation plants in Germany have been handled uniformly as redispatch, often called Redispatch 2.0. At that time the former feed-in management for renewable energies and combined heat and power was merged with the classic redispatch of large power plants. Since then, distribution system operators, including the operators of the 110-kilovolt grids, also carry out such measures. Anyone who speaks of feed-in management today therefore usually means the former regime.

Flexibility relieves the high-voltage grid only if it matches the bottleneck in space and time. A battery behind a different bottleneck does not help against the overload of a particular 110-kilovolt line. A flexible industrial plant, by contrast, can be very valuable: it increases its consumption when a lot is being fed in regionally and reduces it when the grid is heavily loaded. The benefit depends on the position in the grid, not just on installed capacity.

A cost problem follows from this. If bottlenecks are handled by curtailing renewable plants, by redispatch or by temporary equipment, costs arise elsewhere in the power system. If extensive expansion is carried out as a precaution, investment costs arise that are refinanced through grid charges. In the high-voltage grid, therefore, a concrete trade-off is at stake: which infrastructure is built, which flexibility is tapped, which risks are accepted in operation, and who bears the costs?

In short, the high-voltage grid is the regional high-capacity level of the power system. It links higher-level power transport with concrete connections for generation, industry, storage and downstream distribution grids. Those who use the term precisely separate voltage level, grid function, connection capacity and amount of energy. Only then does it become clear whether a problem can be solved by line construction, substations, operational management, flexible demand or other rules for grid connection.

Sources

Energiewirtschaftsgesetz (EnWG) § 3 Begriffsbestimmungen — Bundesministerium der Justiz / gesetze-im-internet.de; unbekannt (aktuelle konsolidierte Fassung). § 3 Nr. 100 (Übertragung) und Definition Verteilung
§ 43h EnWG – Ausbau des Hochspannungsnetzes — dejure.org (Gesetzestext EnWG); unbekannt. § 43h Sätze 1–3
EnWG § 14d Planung und besondere Bedeutung des Verteilernetzausbaus; Festlegungskompetenz; Verordnungsermächtigung — Bundesministerium der Justiz / gesetze-im-internet.de; unbekannt (Fassung nach Änderung mit Wirkung vom 23.12.2025). § 14d Abs. 1–4, 8 und 10
Informationsbereitstellung für Redispatch-Maßnahmen (Pressemitteilung) — Bundesnetzagentur; 2021-03-23. Pressemitteilung, Abschnitt Daten für den Redispatch 2.0
Netzausbauplan 2024 – Bericht gemäß § 14d EnWG der AllgäuNetz GmbH & Co. KG — AllgäuNetz GmbH & Co. KG / VNBdigital; 2024. Netzkarte nach § 14d Abs. 4 EnWG, Gliederung der Netzebenen

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Edited by eCMS on 12.11.2026 05:06