Lines, cables and land

Materials, easements, voltage, undergrounding, maintenance and landscape.

An electrical highway also takes up landscape

Three voltages, three functions within the same grid

Just as a land transport network combines motorways, regional roads and city streets, each designed for a different traffic volume, the electrical grid combines three voltage levels with very different functions. High voltage — from tens to hundreds of thousands of volts — transports large amounts of power over long distances with the lowest possible relative losses, connecting plants and large renewable farms with the main consumption areas. Medium voltage distributes that energy within entire cities and regions, feeding neighborhood substations and industrial parks. Low voltage, finally, is what enters homes and businesses directly, at a level safe for everyday use. Each transition from one level to another requires a transformer, which adds equipment and a small additional loss, but avoids far larger losses than would occur trying to transport power at low voltage over long distances.

What has to be manufactured to string up each type of line

Overhead line conductors usually combine aluminum, for lightness, with a steel core that provides the mechanical strength needed to support its own weight between towers spaced hundreds of meters apart. Underground cables add to that copper or aluminum conductive core layers of electrical insulation and metallic shielding, because a buried cable cannot rely on surrounding air as an insulator the way an overhead cable does. Towers, poles, excavation trenches, substations and the access roads needed for maintenance all require materials and a portion of land that has to be managed throughout the line's service life — insulators, switches, cooling oils and vegetation under the right-of-way are replaced or managed periodically over decades.

Overhead or underground: a choice between two kinds of risk, not between risk and no risk

An overhead line is visible on the landscape, more vulnerable to strong wind, ice buildup, nearby wildfire or vegetation growing too close to the cables — the exact mechanism that started the major 2003 blackout developed in this section's blackout leaf —, but it is simpler and cheaper to visually inspect and to repair when it fails. An underground line reduces visual impact and avoids much of that weather and vegetation risk, but costs considerably more to install, dissipates the heat generated by its own current worse — which can limit its transport capacity relative to an equivalent overhead line —, and locating and repairing an internal fault can take much longer, precisely because the problem is not visible to the naked eye. At sea, submarine cables also have to withstand salt, ship anchors, and constant seabed movement in areas of strong currents.

The route distributes benefits and burdens unevenly

Deciding where a new transmission line runs is not only a technical engineering matter: it distributes benefits — access to electricity generated elsewhere — and burdens — visual impact, land use, possible harm to local biodiversity, wildfire risk in dry forested areas — unevenly among different communities along the route. A responsible decision about a line's route must compare alternative corridors, assess impact on ecosystems and public health, consider local wildfire risk, respect affected property rights, weigh total cost against different technical solutions, and above all, include early participation of the communities that will live alongside that infrastructure for decades.

Neither rejecting every new line nor imposing it without a fair deal

Systematically opposing any new transmission line, without exception, can end up indirectly blocking the deployment of the very clean generation it is meant to defend: a wind or solar farm with no grid connection is useless. But imposing a route without dialogue or fair compensation for the directly affected communities also blocks, in the long run, the energy transition, by eroding the social trust needed to build the next line, and the one after that. This section's challenge is no different from that of the whole energy transition: no infrastructure is free in terms of land, and the only honest way forward is to acknowledge that explicitly and share its cost fairly.

Overhead or underground: two risks, not a risk and an absence of risk

In favor of overhead lines: cheaper to install, easier and faster to inspect visually, and simpler to repair when they fail — still the dominant option for long-haul transmission in most countries.

In favor of underground lines: lower visual impact on the landscape, and less vulnerable to wind, ice, wildfire or nearby vegetation — factors that have caused or worsened several of history's major blackouts.

The cost not always mentioned when asking to "bury all the cables": an underground cable costs considerably more to install, dissipates the heat generated by its own current worse — which can limit its capacity relative to an equivalent overhead line —, and an internal fault can take much longer to locate and repair, precisely because it is not visible to the naked eye.

On the route of any new line: neither systematic opposition to every new line — which ends up blocking the connection of the very clean generation it means to defend — nor imposing a route without dialogue or fair compensation for affected communities are sustainable paths long-term. Early participation and a fair distribution of the territorial cost are, in practice, just as decisive for a project's success as its technical feasibility.

The numbers, with their source

Three voltage levels, three different orders of magnitude

Each transition between levels requires a transformer, with its own fixed and variable losses — developed in this section's Joule-effect losses leaf —, but that extra loss is much smaller than what would occur trying to transport the same power at a lower voltage level over a long distance.

Why a tree can bring down half a country

The major Northeast US and Canada blackout of 2003 — developed in full detail in this section's "Anatomy of a Blackout" data tab — started with a high-voltage line that sagged from the heat of its own current and came into contact with insufficiently trimmed trees beneath its route. That single point of contact, combined with a software failure that delayed operators' response, ended up leaving more than 50 million people without electricity. It is the most cited example of why routine vegetation management under overhead lines — an apparently minor, low-visibility task — is actually one of the most critical grid maintenance activities that exist.

Source: Wikipedia — Northeast blackout of 2003.

What this table is missing

The exact ranges for each voltage level vary from country to country according to their own historical electrical standards; the values in this table are indicative orders of magnitude, not a single worldwide standard.

Sources

• ENTSO-E documents European transmission infrastructure planning, including routing criteria.
• On the role of vegetation near overhead lines in major grid failures: Wikipedia — Northeast blackout of 2003.
• On major submarine high-voltage interconnections: Wikipedia — North Sea Link.