On November 14, 2007, Con Edison, New York City’s electric utility, ceremonially disconnected its last direct current (DC) cable, on 40 Street east of 5th Avenue in Manhattan. Most of Manhattan’s DC service had long before been replaced by the utility’s alternating current (AC) system, pioneered by Nikola Tesla, promoted by Thomas Edison’s rival George Westinghouse, and now standard throughout the world. Con Edison’s ceremony ended a service to New York City customers dating back to Edison’s first DC generating station on Pearl Street inaugurated in 1882.
Westinghouse employed a new invention, the transformer, which operates only on AC current, to step voltage up and down. In contrast to Edison, who envisaged electricity supply as a decentralized, local affair, using numerous low voltage (110 volt) DC generators close to the customers themselves, Westinghouse launched the modern high voltage electric grid in which generation can take place far from load centers. Today, long-distance high voltage AC transmission systems operate at up to 765,000 volts (765kV).
Beginning in the 1920s, ways were devised to convert high voltage AC (HVAC) to or from high voltage DC (HVDC) for similar long-distance transmission, initially using mechanical rotary converters and, later, electronic devices such as mercury arc valves and thyristors. But the greater complexity and custom design of HVDC systems and the difficulty of integrating HVDC with HVAC power grids have, until recently, largely limited its use. Many HVDC systems are point-to-point lines where HVAC would be impractical, such as power supply to islands by submarine cables or interconnections between AC grids using differing frequencies (e.g., 50 Hz and 60 Hz).
Both HVAC and HVDC have their advantages and disadvantages. The power transmission capacity of a line operating with HVDC is about 140% of the capacity of a similar line operating with HVAC. HVAC lines suffer energy losses from induction and capacitance effects. The siting and approval of HVAC lines, which require transmission towers and extensive rights of way, can be expensive and time-consuming. HVDC, having a negligible electromagnetic field (EMF), can be transmitted by a cable several inches in diameter which requires no transmission towers; the cable can simply be laid in the ground or in the bed of an ocean or river (buried HVDC), resulting in lower initial installation costs and relatively simpler land-use and environmental approvals.
But these advantages of HVDC have been offset by the added capital expense and energy loss of the converter stations required at each end of the line. In addition, cables for buried HVDC were, until very recently, designed with a fluid (oil) dialectric as internal insulation, and were thus less reliable than aerial transmission lines. Advances in the design of more efficient and compact solid-state power conversion devices and in the development of solid-dialectric (non oil-filled) DC transmission cables, with greater reliability and lower maintenance, have now reduced the former disparities. In China, two 800kV HVDC lines are currently in service—one built by ABB and the other by Siemens—and more are planned. In this country, improved HVDC technology, expanding renewable energy generation, often far distant from load centers, and the simultaneous growth in market-driven merchant transmission are all combining to spur renewed interest in point-to-point HVDC projects.
Sometime in late 2016, assuming final regulatory hurdles to construction are cleared, direct current will once again be supplied to New York City, this time on a modern, commercial scale. The “Champlain Hudson Power Express” direct-current transmission project (CHPE Project) will provide up to 1,000 megawatts of merchant transmission from Canada to the New York metropolitan area, one of the highest-cost electricity markets in the United States. A cornerstone of the project is a long-term transmission service agreement between the developer and Hydro-Québec for transmission of abundant, low-cost Canadian renewable energy (hydro and wind) to New York over the CHPE Project from as far away as Labrador.
A study by London Economics International estimates that the CHPE Project will reduce electricity costs by more than $650 million a year and produce nearly 2,400 indirect and induced jobs in New York State. It will spur economic development in the state and its GDP by an average of $600 million per year.
The project will be a 400 mile 300kV HVDC buried transmission system comprising a bipole pair of submarine or underground cables running from an HVDC converter station near Hydro-Québec TransÉnergie’s 765/315kV Hertel substation southeast of Montreal to New York City. On the U.S. side, the cable will run south through the lakebed of Lake Champlain for about 100 miles. Thereafter, the cables will be buried on land within highway and railroad rights-of-way and certain state park lands, and laid in parts of the Hudson River, the Harlem River, and the East River, terminating at a proposed HVDC converter station in Astoria, Queens. Estimated to cost around $2.2 billion and backed by the alternative investment giant Blackstone Group, the CHPE Project will be the longest buried HVDC transmission line yet built in the United States.
The CHPE Project developer has received authorization from the Federal Energy Regulatory Commission (FERC) to charge negotiated rates for transmission rights on the project. See Champlain Hudson Power Express, Inc., 132 FERC P 61006, 2010 WL 2636410 (July 1, 2010). As of the date this is written (April, 2013), the developer’s application to the Department of Energy (DOE) for a Presidential Permit (needed for a cross-border facility) currently awaits issuance of a Draft Environmental Impact Statement (DEIS) on this permit, under the National Environmental Policy Act, 42 U.S.C. §§ 4321–4347 (NEPA), by DOE, as the lead agency, anticipated for spring 2013.
The CHPE Project is also pending before New York State’s Public Service Commission (PSC), on the developer’s application for a Certificate of Environmental Compatibility and Public Need (Certificate), pursuant to the State’s Public Service Law. The application is being contested by local energy interests (e.g., Entergy Nuclear Power Marketing, LLC, and Independent Power Producers of New York, Inc.) who, not surprisingly, view the importation of cheaper Canadian energy as a competitive threat. On December 27, 2012, a panel of state Administrative law judges recommended that the PSC grant the Certificate and a water quality certification for the project, on the conditions set out in a “joint proposal” settlement document submitted by the developer and thirteen other stakeholders, including several state agencies, cities, and towns, and conservation nongovernmental organizations (NGOs) including Riverkeeper and Trout Unlimited. A favorable PSC decision is anticipated as early as this spring, although judicial challenge remains possible.
The physical silhouette of the line will be modest: It will entail only a pair of buried cables, about five inches in diameter and three feet apart, with a transmission right of way as little as twelve feet wide (twenty feet in deeper underwater stretches). Environmental impacts from construction in water, to aquatic habitat and biota, as well as terrestrial impacts from on-land construction, are expected to be minimal and transient. In water, the cable will be laid not by dredging but mostly by a technique known as “water jetting,” in which pressurized water creates a slit in the riverbed or lakebed into which the cable is laid, in most places, at a depth of from four to seven feet, from a cable-laying vessel, with the displaced sediment falling back into place behind the cable and burying it. On land, most of the cable will be laid in a roughly three-foot deep trench, backfilled with sand and other protective material.
The low environmental profile of buried HVDC, as compared with HVAC, has implications for the environmental review of future high-voltage transmission developments. Much NEPA alternatives analysis, under Council on Environmental Quality regulations at 40 C.F.R. § 1502.14(a), for electrical transmission projects focuses on alternative transmission routes, with the mode of transmission itself assumed to be some form of HVAC. Wider acceptance of buried HVDC may compel more detailed consideration of alternative transmission technologies as well. Significantly, buried HVDC was recently urged as a project alternative in detailed scoping comments prepared in connection with environmental review of the (since abandoned) Mountain States Transmission Intertie Project.
More broadly, development of cost-competitive and low-impact HVDC transmission would bring significant change to electrical transmission economics, nationally and even internationally. By facilitating access to far distant large-scale renewable energy sources, HVDC may even impact other issues beyond the electric utility sector itself, such as the need of the United States to import oil over the controversial Keystone XL Pipeline. It could turn out to have a more important energy role than even its advocates could have imagined only a few years ago.
Somewhere, Thomas Edison must be smiling.