Transmission & Distribution
From sea to shining sea1 January 2008
Recent progress on sections of AEP’s I-765 project, the so-called Interstate Superhighway, has brought closer the realisation of a wider ambition – the creation of an EHV network that will cover the USA from coast to coast, bringing with it the prospect of steeply increased supply security and power trading on a continental scale.
It is generally agreed that a modern, interstate transmission system is needed in the United States to meet growing electricity demand and to replace or reinforce the existing rather elderly cross country system. But as no national owner/operator exists there is no body that has the responsibility for delivering it. Step forward American Electric Power, the USA’s largest transmission system operator, and by far its largest high-voltage TSO, which in 2006 proposed a major transmission project, dubbed the AEP Interstate Project, to eliminate bottlenecks and allow efficient delivery over a distance of large blocks of competitively priced electricity while enhancing grid reliability. The project is envisaged as a transmission backbone that would overlay and strengthen the existing 345 kV and 500 kV inter-regional systems. The first step has been taken, with the recent approval by PJM (one of two RTOs operating in the north-east of the country) of the PATH section of 550 mile I-765 West Virginia to New Jersey ‘superhighway’. It is expected that ultimately this will connect with the Texas system, creating a transmission highway reaching from the southwest through the Midwest to the eastern seaboard. It would feature the highest-capacity, proven power delivery facilities available, and in its turn form the basis of a national interstate highway, a scheme originally suggested by president Eisenhower in the nineteen-fifties.
In fact such systems have been suggested at regular intervals in the intervening decades, (including that shown in Figure 1) reaching a head in 2005 with a National Energy Policy Act that was accompanied by a call from president Bush for ‘a modern 21st-century electricity grid’; but AEP’s is the first that comes along with its own body of assessments and White Papers.
The existing US grid was created 50 years ago to defeat aging infrastructure, congestion, cost-recovery impediments, siting difficulties and national security concerns. Fast-forward 50 years and aging infrastructure, congestion, cost-recovery impediments, siting difficulties and national security concerns (that is, reliability-compliance concerns) plague the US electric transmission grid once again. The 2005 Energy Act was a step toward but what is really required is a suitable grid of network interconnectors to facilitate a more sustainable national electricity supply system, including tapping the potential of renewable energy generation, stimulating market efficiencies, including reduced congestion, lower line losses, load levelling, enhancing reliability beyond today's minimalist standards, removing supply option barriers, and reducing reliance on the aging infrastructure.
Along with others, AEP believes that to effectively address cost-recovery and siting issues, interstate transmission assets – defined as existing and new transmission at voltages above 300 kV – should be entirely under the purview of the Federal Energy Regulatory Commission (FERC). This includes setting rates with pass-throughs at state retail levels and the siting of new interstate transmission lines. On July 23, 2007, FERC Commissioner Suedeen Kelly said, ‘We need a true nationwide transmission version of our interstate highway system — a grid of extra-high-voltage backbone transmission lines reaching out to remote resources and overlaying, reinforcing and tying together the existing grid in each interconnection to an extent never before seen.’ This is entirely in line with AEP’s own vision – ultimately, an EHV trunk system stretching across the USA from sea to sea. AEP would of course not itself build such a system, but it has undeniably made a start.
A national grid
One possible structure for a national interstate electric transmission grid (Figure 1) has come from a collaboration between AEP and the American Wind Energy Association with the object of creating a conceptual framework for 19 000 miles of new ‘state-of-the-art’ 765-kV lines to link up to 400 000 MW of potential wind resources (Toward a 20% Wind Electricity Supply in the United States 2007, US Department of Energy and National Renewable Energy Laboratory). The cost would be US$60 billion, but consumer costs would be offset by the avoided congestion costs of a robust interstate grid. Transmission is a significant value proposition with typical costs about 8% of the total electric bill.
AEP announced its I-765 interstate concept in January 2006 (Figure 2), with a proposed 550 mile 765 kV line from West Virginia to New Jersey, and its intention to work with others to carry out that plan. Since then, AEP has formed two joint ventures with MidAmerican Energy Holdings Co. – Electric Transmission Texas, LLC (ETT) and Electric Transmission America, LLC (ETA) – to build extra-high-voltage assets in Texas, in the Southwest Power Pool (SPP) and throughout the United States; formed a joint venture with Allegheny Energy – Potomac-Appalachian Transmission Highline, LLC (aka PATH) – to build specific extra-high-voltage assets in PJM zone; and entered into discussions with ITC Holdings Corp to build 765 kV in Michigan and Ohio. These joint ventures would connect to AEPs existing 2100 mile plus 765 kV transmission system.
Along with ABB, AEP will also investigate ways (see panel, above) of reducing 765 kV line losses, which would also reduce the need for new generation. But the collaboration does not end there. Although AEP’s current 765 kV lines exhibit considerably lower line losses than the original 1960s design, averaging in the 3% range, (and with the most recent designs even that figure has been reduced by 40%) the two companies are also to pursue further 765 kV development, including the consideration of creative off-ramps to accommodate wind access, urban areas and limitations of existing local networks.
‘Our goal is to reduce line losses even further,’ says AEP transmission vp Mike Heyeck.
Wyoming-Jacksons Ferry project
The company’s new six-bundle conductor configuration was deployed successfully on the 90-mile Wyoming-Jacksons Ferry 765 kV transmission project that was energised in June 2006 by Appalachian Power connecting power stations in Wyoming County, Western Virginia, and Jacksons Ferry, Virginia. The new line immediately improved electric reliability in a part of the company’s West Virginia and Virginia service area that had not seen major reinforcement in more than 30 years.
Energising the Wyoming Jacksons Ferry project brought to conclusion one of the longest standing transmission construction projects in the US. AEP first proposed construction of a new transmission line to serve its growing southern West Virginia and southwest Virginia customers in 1990. Ultimately, the $306 million project took 13 years to permit and just under three years to construct.
Why 765 kV?
In formulating the I-765 project, AEP considered the available transmission technologies, including DC. The guiding principle has been the project’s goal to provide the reliable transmission capacity and operating flexibility required of a competitive electricity marketplace. Unsurprisingly but perhaps not significantly AEP’s assessments have all produced the same result – system architecture based on the model of its existing 765 kV network, which is installed mainly around the Midwest Great Lakes region in West Virginia, Indiana and Ohio.
In three White Papers between August 2006 and September 2007 AEP discussed the key physical and economic attributes of 765 kV and 500 kV transmission options in general, and specifically as related to the company’s Interstate Project.
Studies carried out by AEP and others (Figure 5) show that a 765 kV, 250-mile line, representative of each of the two segments comprising the AEP project, can carry substantially more power than a similarly situated 500 kV line. The load carrying ability, or loadability, of a double-circuit 500 kV line can approach that of a single-circuit 765 kV, but the resulting design would be more a massive structure, with the associated construction challenges, cost premium and visual impacts.
Experience also indicates that transmission systems designed for 765 kV operation are inherently more reliable than those operating at lower voltage levels. With up to six conductors per phase, the 765 kV lines are virtually free of thermal overload risk, even under severe operating conditions. Moreover, outage statistics show that 765 kV circuits, on average, experience significantly fewer forced outages than their 500 kV counterparts, with no multi-phase faults recorded at 765 kV in normal operation. These properties suggest a lower probability of disruptions at 765 kV, and of lower severity, and an opportunity to apply effective remedies to further improve line (and thus system) reliability.
Preliminary estimates place the cost of the first phase of the AEP Interstate Project at approximately $3 billion. Two-thirds of this amount is required for the construction of a 550-mile, 765 kV line, the cost of which would rise by a factor of 1.4, to $2.8 billion, if it was built as a double-circuit 500 kV alternative. The remainder represents line siting, certification and right-of-way acquisition (about 20%), and station construction and equipment (10-15%) at the line terminals. Assuming no change in the ROW cost, the increased amount in combination with the ROW cost alone would exceed AEP’s original 765 kV cost estimate, even if none of the required station facilities were considered.
Since the project is in a conceptual phase, station costs are not yet well defined. Such costs include switchgear, transformation as well as shunt/series reactive compensation that might be required for local voltage support and/or loadability enhancement. With its higher loadability and greater reactive power capacity, significant cost advantages of the 765 kV transmission versus 500 kV are expected and will become still more apparent as the initial 765 kV ‘superhighway’ evolves into an integrated network.
Progress of I-765
AEP expects I-765 to be operational by around 2015, and has received approval from the system operator PJM (Pennsylvania-New Jersey-Maryland) for a substantial section of it.
As originally proposed this transmission superhighway would reach approximately 550 miles. It was designed originally to reduce congestion costs in the PJM region by substantially improving transfer capability – in fact by approximately 5000 MW, with transmission line losses reduced by about 280 MW.
In June 2007 PJM Interconnection approved a proposal put forward by AEP and Allegheny Energy to build a significant portion of the superhighway. The Potomac-Appalachian Transmission Highline (PATH) will involve the construction of 250 miles of 765 kV EHV transmission in West Virginia and an additional 40 miles of 500 kV transmission from West Virginia to Maryland.
AEP is proposing that its transmission company, LLC, develop the 765 kV project. The line will employ all available technology to optimise corridor performance and minimise environmental impact. It will cost approximately $3 billion. The projected in-service date is 2015, assuming three years to site and obtain certifications, and five years to construct.
Since its inception a new scheme to connect the 765kV system to the islanded Michigan/Northern Ohio area has been devised, which will have the effect of connecting the Midwest grid to the Northeast (PJM) network, allowing flows of up to 5000 MW in either direction and ending the isolation of the lower Michigan area.
The Michigan connection
AEP and ITCTransmission, a subsidiary of ITC Holdings Corp, signed in 2006 a memorandum of understanding (MOU) to perform a technical study evaluating the feasibility of extending AEP’s 765-kV transmission infrastructure through Michigan. This resulted from a decision by the state of Michigan that it needed to improve its transmission infrastructure. AEP, the major operator in the area agreed, and has produced two White Papers outlining the case for expanding the high voltage system and for using a 765kV AC system to do it (Figure 7).
The project addresses the need for transmission upgrades in the southeastern region of Michigan, providing a platform for further reinforcement of transmission both in the northern region of the Lower Peninsula and in the Upper Peninsula and for increasing Michigan-Ontario interface capacity without overburdening other portions of the ITC grid.
One of the challenges associated with lower Michigan’s existing electrical infrastructure is geographic: Michigan is a peninsula and currently its electric supply is also ‘islanded’. It is important that Michigan does not remain an electric supply peninsula. But Michigan, like much of the US, has under-invested in its electrical infrastructure for many years. To make matters worse, results from the Michigan Public Service commission (MPSC)’s Capacity Needs Forum and preliminary results from the MPSC’s 21st Century Energy Plan study make it apparent that Michigan’s future power needs will soon outstrip its current power supply and transmission infrastructure.
Currently, the MPSC is constructing an energy plan to address these future needs. Fossil generation, renewable generation, alternative technologies and energy efficiency all are being studied for the role they can play, a well as transmission, a critical component. The commission believes that a robust 765 kV AC transmission grid will not only improve reliability and capacity in its own right, it will magnify the benefits of other solutions – including new generation – by integrating them into a regional network of resources, in which scale and capacity provide a ‘self-healing’ safety net that ensures one resource can quickly compensate for the absence of another in times of need.
AEP and ITC Holdings believe that development of a Michigan EHV grid will enhance reliability, improve system efficiency and improve efficiency of generation markets. They also believe 765 kV technology is a superior alternative to other transmission technologies and to that of merely adding new generation in the state. In September the two companies released the results of their joint technical study evaluating the feasibility of extending the 765 kV infrastructure through Michigan. The study results recommend building three segments of extra-high voltage 765-kV regional transmission in PJM Interconnection (PJM) and Midwest ISO (MISO) that would extend AEP’s existing 765-kV transmission system in the southwest corner of the Lower Peninsula of Michigan east across Michigan and south to the existing 765-kV infrastructure in Ohio. If built as recommended, the project would total approximately 700 miles, about 420 miles in Michigan and 280 miles in northern Ohio.
The study proposes a 765-kV transmission line entering Michigan from the south up to a new transmission station to be built west of Detroit, followed by a segment that would cross Michigan from west to east connecting the D.C. Cook Nuclear Plant at Bridgman to Detroit, and then a third transmission line that would enter Michigan from the southeast near Canton, Ohio, and extend northwest to Detroit.
AEP believes that its existing 765 kV network is the logical foundation for this effort. The company already operates 2100 miles of 765 kV lines in the East, the Midwest and Texas,CHECK REPETITION and considers it to be highly efficient and reliable especially where space for permitted corridors is at a premium.
High-voltage AC transmission infrastructure is an essential platform for both economic development and reliability. It:
• Improves efficiency of competitive generation markets by relieving congestion,
• Creates a more reliable, self-healing grid,
• Mitigates generation market power, and
• Is critical to the efficient and economical operation of the entire electric system.
AEP-ABB R&D in EHV
American Electric Power has entered into an alliance with ABB to develop what the two companies are calling ‘advanced technologies to enhance 765 kV EHV transmission’.
The alliance involves a non-exclusive collaboration to study and bring to market new designs, equipment and systems for potential deployment on the AEP transmission system and across the industry. The two companies will establish teams of technical experts to co-ordinate identification, development and engineering of advanced technologies to improve current designs and support development of a more robust interstate transmission grid.
Michael Heyeck, an AEP senior vp, said ‘ABB played a key role in developing our current transmission grid and collaborated with AEP on ultra-high voltage (above 1000 kV) research in the 1970s and 1980s. Collaborating with ABB on this effort will bring together some of the world’s transmission experts ... and [help achieve] our vision of creating the most reliable, efficient transmission network possible.’
Some of the technology concepts that AEP and ABB will explore include:
• Independent phase operation to enable each of the three phases of transmission lines to operate independently so that only a faulted phase remains open to allow for reliable redispatch of the system. Typically, all phases of a line trip for any fault.
• Next-generation substation automation and equipment to enable smart grid controls and improved equipment performance.
• Creative ‘on ramp’ and ‘off ramp’ substation configurations for 765-kV transmission to allow connection to existing systems in urban areas and to accommodate distributed generation resources, such as wind, and to address other network limitations.
AEP and ABB also will investigate methods for reducing 765-kV line losses, which consequently will reduce the need to build new generation.
‘Compared with average transmission line losses of three percent, line losses on the newest
765-kV transmission lines already have been reduced by 40 percent to less than 0.75 percent as a result of our new six-bundle conductor configuration. Our goal is to reduce line losses even further’ Heyeck said. The six-bundle conductor configuration was deployed on AEP’s 90-mile Wyoming-Jacksons Ferry 765-kV transmission project that was energised in June 2006.