Tres Amigas : A flexible gateway for renewable energy exchange between the three asynchronous AC networks in the USA

摘要

Tres Amigas is an ambitious and innovative project to provide a three way 5000MW interconnectionbetween the three independent networks in the USA. The electric grid in the USA is operated as threeseparate asynchronous 60Hz systems, covering the western states (WECC), eastern states (EasternInterconnected System) and the state of Texas (ERCOT). The only connections between thesesystems presently, are through a series of small and now ageing, HVDC back-to-back stations.Located near the border of New Mexico and Texas, the Tres Amigas Super-station will consistultimately of six HVDC back-to-back converter stations, which can be configured to connect to eachof the three AC systems. The scheme will transport power across the links to exploit the differences inenergy process on the three regions. More significantly, because of the much higher power rating thanis presently available through the existing links, it will allow a much broader reach for exchange andtrading of the high levels of renewable energy which are expected to be realized in the near futureacross the region.The initial three converter stations will be built using VSC HVDC technology to provide up to2250MW of transmission capacity, since VSC has the benefit of being capable of operating reliably,despite the relatively weak 345kV systems in the proposed site area. To improve the AC infrastructurein the region and allow the station to export renewable energy, new 500kV and possibly 765kV lineswill be built over time, which will strengthen the networks, and it is envisaged that these stronger ACsystems will allow the remaining three converter stations to be built using LCC HVDC technology.The LCC stations can be designed with high levels of continuous and short-time overload capability tomaximize the power transfer capability of the scheme during a scheduled or forced outage of a singlepole.Although the first stage of the installation is being designed as a single link, the system is planned withoperational flexibility and future expansion in mind, and facilities are being incorporated into thedesign which will allow for this, including an accessible DC busbar in the back to back circuit. Thereis the potential to incorporate other novel features in the future including large-scale battery energystorage and eventually superconducting cables. The first stage and each of the future 5 stages will becapable of independent, individual control, and they may also be placed under the control of an overallcoordinating controller in the form of an operational and market management system.When the six HVDC links are fully installed this will potentially provide energy gateways for up to5000MW of power to be exchanged between the three regional AC networks in effectively a multiterminalconfiguration. A key feature of the Tres Amigas development and operating principle is maximum use of renewableenergy, not only in the HVDC power transmitted but also in the operation of the superstation itself.The station will both transmit and make use of wind, solar and other available forms of renewableenergy throughout the regional AC networks.Construction is anticipated to start in mid-2012, with the individual poles being commissioned from2014 onwards. When completed this will be the largest back-to-back HVDC installation in the world,and a unique facility to enhance the transmission network in the USA.