Electric Transmission Market Boom: Grid Transmission Market for Urban Infeed and Congestion Relief

The electric transmission market is solving urban power constraints with HVDC. Discover how the grid transmission market uses buried HVDC cables to deliver power into dense cities without new overhead lines.

Cities are the world’s engines of economic growth, but they face a critical constraint: getting enough electricity into dense urban areas without building unsightly new overhead transmission lines. Land is scarce, property values are high, and public opposition is fierce. The electric transmission market for urban infeed has turned to HVDC. The grid transmission market now includes buried HVDC cables and compact converter stations that can “inject” large amounts of power into cities from distant renewable sources or existing grid nodes. This article examines the niche but growing application of HVDC for urban power delivery.

The Urban Transmission Problem

Most high-voltage transmission lines are overhead—towers and wires. Overhead lines are cheaper, easier to maintain, and have lower losses than underground cables. However, in dense urban areas, it is often impossible to build new overhead lines. There is no space for towers, property owners resist eminent domain, and the visual impact is unacceptable. Undergrounding AC cables is possible, but AC cables have charging currents that limit their length and capacity, and they are more expensive per km than overhead lines. HVDC cables do not have charging currents, can be buried for long distances, and have lower losses than AC cables for the same rating. Thus, the hvdc transmission market provides a solution for urban infeed.

How Urban HVDC Infeed Works

A typical urban HVDC infeed system:

1. Source: Power is tapped from the existing AC grid at a rural or suburban substation.

2. Converter station: AC is converted to DC at the source end.

3. Buried DC cable: A high-voltage DC cable (typically ±200 kV to ±320 kV) is laid along roads, under sidewalks, or through tunnels. Because it is DC, there is no charging current, and the cable length can be tens of kilometers.

4. Urban converter station: At the city center (or near a substation), the DC is converted back to AC and injected into the urban distribution grid.

The urban converter station is often a voltage-sourced converter (VSC) , which is compact and can be built indoors or in a small footprint.

Examples of Urban HVDC Projects

• TransBay Cable (San Francisco, USA): ±200 kV, 400 MW, 85 km. Connects an AC substation in the East Bay to a converter station in downtown San Francisco. Power is transmitted via buried DC cable primarily under the San Francisco Bay (submarine) and then underground in the city. It avoids building new overhead lines through San Francisco.

• Murraylink (Australia): ±150 kV, 220 MW, 180 km. Buried DC cable between two substations in Victoria and South Australia, passing through urban and rural areas. Not strictly urban infeed but demonstrates underground capability.

• East-West Interconnector (Ireland/UK) and others have urban landing points.

• SVC Light and HVDC Light (Hitachi Energy) are specifically designed for urban infeed and weak-grid connections.

The grid transmission market for urban HVDC is growing as cities replace aging infrastructure and integrate distributed generation.

Converter Station Footprint

A key advantage of VSC technology for urban infeed is its compact footprint. An LCC station requires large AC filters and reactive power compensation equipment, often occupying several hectares. A VSC station can be built indoors on a smaller footprint (e.g., 50 x 100 m). For example, the TransBay Cable converter in San Francisco is located in a urban industrial area, not a remote rural site. The hvdc transmission market for VSC has enabled HVDC to enter urban real estate.

Cost Comparison: HVDC vs. Underground AC

For a given power rating and distance, underground HVDC cables are generally more economic than underground AC cables for distances over about 50-80 km. For shorter distances, AC may be cheaper. However, for urban infeed, the alternative to HVDC is often not underground AC—it is no new transmission at all. In that case, the value of HVDC is the ability to unlock stranded renewable generation or relieve congestion. The long distance power transmission market for underground HVDC is evaluated on a project-by-project basis.

Congestion Relief and Grid Access

Urban grids often suffer from congestion: certain transmission lines are overloaded, limiting the amount of power that can flow into the city. HVDC can act as a “transmission bridge,” bypassing congested paths. For example, an HVDC line can bring power from an underutilized generation area directly to the city, bypassing the congested grid. This is sometimes called a “merchant transmission” or “point-to-point” bypass. The electric transmission market for merchant HVDC is small but high-value.

Converter Station Siting Challenges

Even compact VSC converter stations face siting challenges in dense cities. They require a large electrical footprint (transformers, valves, cooling systems). They may cause noise (fans) or visual impact. They must be connected to both the DC cable (which must be routed through streets) and the AC distribution grid. These challenges can be managed with careful engineering and community engagement. The grid transmission market for urban infeed often involves tunnel construction for the DC cable, which is expensive.

HVDC and Distributed Generation

Cities are also installing distributed generation: rooftop solar, cogeneration, and battery storage. In some cases, HVDC can help collect power from multiple distributed sources and feed into the grid. However, most distributed generation is at low voltage, and aggregation is more practical with AC. The hvdc transmission market for urban distributed generation is not significant today.

Voltage Levels and Safety

Urban HVDC cables are buried, so there is no electric shock risk to the public (assuming proper insulation and depth). However, DC cables can cause interference with other underground utilities (gas pipes, water mains, communication cables) due to stray currents. Proper cathodic protection and shielding are required. The long distance power transmission market for urban cables includes rigorous planning and coordination with other utilities.

Future Trends: Multi-Terminal Urban Infeed

A future development could be a multi-terminal HVDC ring around a city, with multiple points of infeed and power sharing. For example, several radial HVDC links from different sources could terminate at different points, and a DC loop could interconnect them, increasing reliability. This would require DC circuit breakers and control systems. The grid transmission market for urban multi-terminal HVDC is speculative but intriguing.

Policy and Regulation

Urban HVDC projects often face regulatory hurdles: permitting for cable trenches, environmental impact assessments, coordination with multiple jurisdictions, and rate-base treatment (recovery of costs through transmission tariffs). However, in regions with high renewable penetration and grid constraints, utilities and regulators have approved such projects. The electric transmission market for urban infeed requires supportive policy.

Conclusion: HVDC in the City

The hvdc transmission market for urban infeed is a small but growing niche. It solves a specific problem: getting large amounts of power into dense cities without new overhead lines. As cities decarbonize and electrify (electric vehicles, heat pumps), their peak power demand will grow, and the need for urban infeed will become more acute. HVDC, with its buried cables and compact converters, is well-suited to meet this need. The grid transmission market of the future will include more HVDC cables under city streets. Access the complete electric transmission market analysis for urban applications here.

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