Technology  »   Power Transmission Without the Power Electronics By Peter Fairley

GE's variable-frequency transformers transfer power between out-of-sync grids without the problems of semiconductor power electronics


14 November 2007—During their low-resolution beginnings, digital music and photography delivered a jarring rendition of sounds and images, full of noticeable discontinuities. Today, you get the same sort of thing from semiconductor-power electronics devices used to manage power flows on high-voltage transmission grids, and those jarring oscillations can damage the high-precision turbines spinning in power plants. This costly problem inspired engineers at General Electric Co.'s Atlanta-based GE Energy division to go back to the future and create a new semiconductor-free-power control device: the variable-frequency transformer, or VFT.

U.S. electricity giant American Electric Power (AEP) started up GE's first commercially produced VFT this summer in Laredo, Texas, to pull in up to 100 megawatts of emergency power from Mexico. Montreal-based Hydro-Québec has been operating a demonstration VFT since 2004 to manage power exchanges with the eastern U.S. grid. By 2010, three more VFTs should be operating in New Jersey to push extra power into chronically undersupplied New York City.

VFTs and power electronics manage power flows by reshaping AC power waves. They can thus bridge grids whose 60-hertz frequencies are out of sync with each other, such as those in Mexico and Texas, or they can drive power from one line to another by synthesizing ac waves that are out of phase with respect to one another, exploiting a phenomenon known as “phase angle” that is a grid operator's primary tool for directing power flows.

Complete Article :

http://spectrum.ieee.org/nov07/5714