American Superconductor (resistive HTS FCL)

American Superconductor (AMSC) is designing a 138 kV-class, 1200 Arms, resistive HTS FCL that will be demonstrated on the electric grid by the utility Southern California Edison in 2012. The Devens, Massachusetts-based company is collaborating with four partners to build this three-phase, transmission-level FCL called the SuperLimiter. The partners expect to demonstrate a single-phase FCL in 2010. AMSC selected resistive FCL technology because of its simpler design, compactness and cost-effectiveness. The SuperLimiter will use second generation (2G) HTS wire and a modular design that can be easily adjusted for site-specific requirements. The goal is to reduce fault currents between 20% and 50%. Other private companies and public entities involved in the project include Nexans of France, Siemens AG of Germany, the University of Houston and Los Alamos National Laboratory.

SuperPower (resistive HTS FCL)

SuperPower is designing a 138 kV, 1200 Arms, three-phase resistive HTS FCL that will be installed and operated by 2012 on the electric grid by American Electric Power, an Ohio-based utility. Two single-phase protoypes are being tested in labs. What's called the Superconducting Fault Current Limiter features a matrix design with conventional copper coils and parallel second generation (2G) HTS wire. The Schenectady, New York-based company has designed its FCL with a cold shunt coil so the device can be self-contained and not require external or ancillary equipment. Also, the device is being designed to recover quickly under load current so it does not need to be taken off-line. Other private and public partners involved in the design include Sumitomo Electric Industries, Nissan Electric Co., both of Japan, and the Oak Ridge National Laboratory. The goal is to reduce fault currents between 20% to 50%.

Zenergy Power: (inductive HTS FCL)

San Francisco-based Zenergy Power is the first company to have an FCL operating on the U.S. electricity grid. The California Energy Commission (CEC) funded the project. This 15kV, 1200 Arms, three-phase saturable iron core HTS FCL was installed in Southern California Edison's Avanti Circuit in March 2009. The neighborhood circuit, which powers about 1,400 homes and businesses, serves as a testing ground for modern grid technology. Zenergy's device weighs 40,000 pounds, and measures 8 feet by 12 feet and is 9 feet high. It reacts within the first quarter-cycle (one-quarter of one-sixtieth of a second) after detecting a power surge. The goal is to reduce fault currents 30%-50%. Though this model uses first generation (1G) wire, it also can accommodate second generation (2G) wire. It uses only one DC HTS coil for a three-phase AC unit. That means it requires very little HTS material and has a low "cryogenic overhead," which includes such expenses as cryostats, coolers and liquid nitrogen equipment.

 
Zenergy's fault current limiter operating in the Southern California Edison's Avanti Circuit.

Zenergy and several public and private partners are in the midst of developing a 138 kV, 2000 Arms, saturable iron core HTS FCL that could be installed on a transmission grid by September 2011. This project is being developed in three phases, and builds on Zenergy's other FCL initiative with the California Energy Commission. The first phase entails constructing a 6 kV sub-scale design that is small and light. Next, a medium voltage model would be built and tested with a utility partner. After that, Zenergy will build a 138 kV FCL to be tested on a circuit of a city yet to be selected. The goal would be to reduce fault currents by 30% to 50%.

Electric Power Research Institute (solid state FCL)

The California-based Electric Power Research Institute (EPRI) is under contract with DOE to develop a 69 kV, 1000 Arms, single-phase solid state FCL in 2009. Silicon Power Corp. of Malvern, Pennsylvania, is the subcontractor on this initial single-phase design that will be tested in a lab. If it functions successfully, it will be upgraded to a three-phase solid state FCL and then tested in the electric grid. Designed to look similar to a transformer, the device weighs 80,000 pounds. Its main enclosure measures 12 feet-by 12 feet and is 12 feet high. It can be controlled locally or remotely, and operates without cryogenics. The super gate turnoff thyristor semiconductor switches built into its operating system are intended to allow for lower losses, reduced overall size and weight, and the ability for the FCL to rapidly change from a low impedance state to a high impedance state. A modular design means it can be expanded to accommodate desired voltage and current ratings. The goal is to reduce fault currents between 50% and 60%.