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A multi-channel Variable Frequency Transformer (VFT) has been commissioned in Linden, New Jersey to provide control of 300 MW into New York City. The first two VFT installations, at Hydro-Québec's Langlois substation and at AEP's Laredo substation, are single-channel applications, and the Linden VFT is the first multi-channel VFT, with three channels in parallel. The core technology of the VFT is a rotary transformer with three-phase windings on both rotor and stator. The power flow through the VFT is controlled with a motor and drive system which adjusts the rotational position of the rotor relative to the stator. Although the VFT can interconnect two asynchronous power grids, the Linden VFT is connected between synchronous systems that have existing ties. The VFT was the preferred technology chosen for the Linden application because of its ability to continuously control power flow, its low risk of grid interactions, and its relatively small physical footprint. This paper describes the VFT application at Linden and demonstrates its performance and seamless integration.

This paper discusses various applications where VFT technology can be used as a tie between power system control areas.Its use to facilitate connections between synchronous and asynchronous systems is discussed along with its general operational characteristics in these applications. The VFT's ability to be used as a tool for fulfilling various operational objectives, such as providing loads access to lower cost generation areas, reserve sharing, enhancing operational flexibility, grid stabilization, and paralleling of existing HVDC ties is discussed in terms of technical characteristics and typical concepts associated with the design and operation of these interconnections. Related concepts for use of the VFT system for control of both real and reactive power, integration into existing control areas operations, and inclusion in power system market operations and dispatches are also included.

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