The Variable Frequency Transformer (VFT), along with related facilities, was the first transmission asset transferred to the Electric Transmission Texas joint venture between subsidiaries of American Electric Power (AEP) and MidAmerican Energy Holdings Company (MidAmerican).
The 100-megawatt VFT was installed at the Laredo Substation to help improve reliability in the Laredo area and substantially decrease the need to operate expensive Laredo area power generation, which has been designated "RMR" (reliability-must-run) by agreement between the local generation owner and the Electric Reliability Council of Texas (ERCOT). The VFT at Laredo is the second installed in the world and the first in the United States.
The VFT established an asynchronous transmission link between AEP’s Texas Central Company (TCC) and Mexico’s Comisión Federal de Electricidad (CFE). The VFT technology provides a controlled transmission path between the ERCOT and the CFE electrical grids, permitting power exchange that was previously impractical due to asynchronous boundaries. GE Energy’s VFT technology provides an innovative alternative to back-to-back high voltage direct current converters by allowing customers to control power between two asynchronous grids with less risk than with conventional technologies
Although the VFT concept is relatively new, the VFT itself is comprised of well-established hydro-generator, motor and variable-speed drive technology. The Laredo project is the first VFT established in the United States and the second in the world. It consists of a rotary transformer that provides a continuously controllable phase shift for any angle, and a drive system and control that adjust the angle and speed of the rotary transformer to regulate power flow. The individual, 100-megawatt VFT channels can be combined in increments to meet a particular load situation.
When combined with a new 345-kV transmission line that has been approved by ERCOT and expected to be completed in 2010, the VFT and related facilities decrease the need to operate the costly Laredo generating plant and support the load growth in the Laredo area. Compared to the other options considered, the VFT provides the highest degree of flexibility. It allows the scheduling of power transfers in high load periods prior to completion of the 345 kV line, while maintaining a reliable power supply for the Laredo area.