Distribution Automation Applications

Fault Location, Isolation, and Service Restoration (FLISR)

Automatically minimize the impact of outages—within seconds.

What Is FLISR?

Fault location, isolation, and service restoration (FLISR) automatically restores power to as many customers as possible, as quickly as possible, in the event of a permanent fault. Without a distribution automation solution like FLISR, that outage must be handled manually, often resulting in an outage larger (in size and duration) than necessary.

Deploying FLISR makes it possible to improve coordination of switching devices already present for protection or sectionalization purposes on the electric power system and extend their utility into post-fault restoration.

Whether relying on a recloser’s own local sensing and logic or communicating with a sophisticated computing platform running FLISR software, those switching devices can be used to isolate a permanent fault, minimize the size of the outage, and restore load from adjacent feeders in a matter of seconds. Implementing a FLISR solution can also help improve reliability indices such as CMI and SAIFI.

How Does FLISR Work?

Permanent faults are de-energized by protective relays that open and lock out breakers or reclosers. This lockout creates an outage for the faulted zone, any customers downline of the faulted zone, and—if any kind of miscoordination occurs—customers upline of the faulted zone, as well. FLISR’s purpose is to locate that fault, isolate it by opening bounding switching devices, and restore as much load as possible by closing one or more open points between the faulted feeder and neighboring feeders. FLISR solutions can most simply be divided into the following three categories:


Many distribution feeders are protected by recloser controls that are not augmented with a communications system. It is possible to implement FLISR functionality using local sensing of voltage and current, coupled with close-onto-fault relay logic. This noncommunication FLISR solution allows reclosers and switches located on a two-feeder radial loop to take restoration action after a permanent fault has resulted in lockout. This solution is best paired with a noncommunication high-density coordination scheme, which automatically resolves planned or unplanned miscoordinations.

Peer-to-Peer With Communications

The peer-to-peer FLISR solution is designed for similar system topologies as the noncommunication solution (a two-feeder radial loop), but the addition of a communications system eliminates the necessity of close-onto-fault logic, and if the communications system is protection-speed, the restoration time can be drastically improved. This relay-to-relay solution, often called high-speed loop sectionalizing, is a simple solution that places no limits on the number of switches or reclosers in series on a radial loop.

Regional and Centralized

More centralized FLISR solutions utilize software and computing platforms capable of communicating with breakers, reclosers, and switches to gain wide-area system visibility. Designed to scale to hundreds or thousands of switching devices, these FLISR solutions are generally deployed in either the substation or distribution control center. Software-based FLISR solutions make it possible to rapidly and economically deploy FLISR across a wide area containing complex and unique distribution feeder topologies.

From our knowledge base

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We've collaborated closely with our customers since the company was founded nearly 40 years ago. And it’s a major reason why we’re North America’s most trusted provider of protective relays and ranked #1 by international utilities in price, service, and support.

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