Why HVDC cables are poised to provide valuable alternatives

stock.adobe.com/Aleksandr Matveev

The ability to efficiently move substantial amounts — more than 1,000 megawatts — of power from generating sites to load centers is fundamental to large-scale electrical infrastructure. In the United States, this has historically been performed by high-voltage alternating current (HVAC) transmission lines. High-voltage direct current (HVDC) transmission often has been deployed in many other parts of the world, but it has never caught on in a big way in the U.S., largely because of cost considerations.

As renewable generation sources continue being added to the grid from widely dispersed locations that are often farther from load centers than traditional baseload plants, more power needs to travel farther to satisfy growing demand. One advantage of HVDC cables is it can transport more power farther without the dielectric or capacitive losses experienced by AC cables over very long distances.

DC also offers greater flexibility than AC to allow connection of asynchronous grids, while providing stronger grid protection to keep faults from propagating from one grid to the next.

And one of the strongest arguments for utilizing HVDC is that it can be deployed underground over long distances in a much narrower right-of-way (ROW) than overhead transmission lines. Instead of a 150- to 300-foot-wide ROW for a high-voltage overhead line, an underground HVDC cable with similar capacity can be installed in a 10-foot ROW. Even factoring in temporary 50-foot construction easements, this provides a narrower path and reduced impact at the same time it also provides a system that is highly resilient against extreme weather, vegetation interference and potential pushback from local residential and commercial landowners. When the higher upfront costs of underground installation are weighed against the maintenance costs over the life of an overhead line, underground HVDC becomes much more cost-competitive.

Some market limitations remain that must be overcome before HVDC penetration can reach its full potential:

The U.S. market is not going to suddenly turn from HVAC to HVDC for transmission, but there is ample opportunity — and justification — for increased applications of the latter. As utilities and developers strategize for an increasingly distributed, increasingly renewables-based power portfolio, the potential of HVDC looks poised to drive new solutions for old constraints.