Fault Current Limiter (FCL) – More Information A fault current is the term utilities use to describe what happens when an excessive amount of current flows in an uncontrolled manner through the electrical system. These sudden, stronger-than-normal currents pulsing through the system are triggered by an unintended short-circuit or partial short-circuit in an electric circuit. Some of the causes of faults include lightning strikes, contact between power lines and tree branches, and downed or crossed power lines.

Fault currents can create major problems for electric utilities because they interrupt the flow of power to customers. They can damage or degrade transmission and distribution equipment that is expensive and time-consuming to repair. FCLs can extend the life of substation equipment without utilities having to upgrade vital components such as circuit breakers and transformers.

FCLs have the potential to provide a long list of benefits to utilities. Key among them are:

• Enhancing the safety, stability and efficiency of power delivery systems
• Reducing maintenance costs of transmission and distribution equipment
• Deferring investments to upgrade or replace existing transmission and distribution equipment
• Preventing or eliminating blackouts and disruptions
  
  At this time, FCL technologies fall into two broad categories:
• High-temperature superconducting (HTS) FCLs: These FCLs incorporate two different types of technologies to "absorb" a fault current so circuits can pass only safe levels of current or reroute power to protect utility equipment. HTS FCLs require a cryogenic cooling system to allow the HTS material to operate in its superconducting state.
  
  Two types of HTS FCLs—one resistive and the other inductive—are now being researched and tested. Resistive devices use specially designed superconductors to absorb fault currents. Inductive devices stop fault currents by using superconductors and iron cores in combination to absorb any excess current.
  
• Solid-state FCLs: This design limits the current by using semiconductor switches to divert electrical energy to a higher impedance pathway within microseconds of detecting a fault current. The higher impedance path absorbs the fault current before it can harm utility equipment.
  Currently, the Department of Energy's Office of Electricity Delivery and Energy Reliability is funding four different FCL research projects. Three of them are HTS projects and one is a solid-state project. In addition, the California Energy Commission is funding a separate HTS project that will serve as a building block to DOE's work.

More information on current projects >

FCL Testing Standards

No standards yet exist for testing prototype high-temperature superconducting (HTS) and solid state FCLs or for integrating them into the electric grid. In the meantime, FCL device manufacturers, their utility partners, academia, research institutions and the federal government are collaborating to develop the necessary testing procedures. Most likely, these procedures will vary, depending on the design and application of the equipment.

A newly developed FCL Testing Task Force, under the umbrella of the Institute of Electrical and Electronics Engineers (IEEE), is compiling a guide to address these testing requirements.