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:

Noncommunication

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

FLISR Without Communication

Consider the following event: a permanent fault occurs between Recloser 1 (R1) and Recloser 2 (R2) on a two-feeder radial loop. R1 will observe this fault, attempt to clear the fault according to its reclose settings, and eventually lock out when those reclose attempts are unsuccessful.

The open tie point recloser (R3) will sense the loss of voltage caused by the opening of R1, and after sufficient time has passed, it will automatically close, re-energizing the line in the direction of R2. The closing of R3 re-energizes the permanent fault location. This is known as close-onto-fault logic.

Once R3 closes, R2 will observe fault current and will immediately trip and lock out. This results in an isolated permanent fault zone between R1 and R2, and restored load between R2 and R3.

Without this FLISR implementation, the outage created by this permanent fault is larger than it needs to be and could take hours to detect and mitigate. Enabling switching devices to detect the outage using local sensing and logic reduces the outage reaction time to minutes.

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Peer-to-Peer FLISR Solution

Consider the following event: a permanent fault occurs between Recloser 1 (R1) and Recloser 2 (R2) on a two-feeder radial loop. R1 will observe this fault, attempt to clear the fault according to its reclose settings, and eventually lock out when those reclose attempts are unsuccessful.

Instead of relying on local sensing, R2 receives a message directly from R1 informing it that a permanent fault exists and that R1 is now open. R2 can quickly open to isolate the fault and send a signal to R3.

R3, upon receiving a signal requesting a source to close from R2, closes, re-energizing the zone between R2 and R3.

This FLISR solution, often called high-speed loop sectionalizing, employs protection-speed communications and can perform FLISR functionality on a radial loop topology in milliseconds.

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Software-Based Wide-Area FLISR Solution

Consider the following event: a permanent fault occurs between Recloser 1 (R1) and Recloser 2 (R2) on a two-feeder radial loop. R1 will observe this fault, attempt to clear the fault according to its reclose settings, and eventually lock out when those reclose attempts are unsuccessful.

Each switching device every feeder in the region or system is communicating with an automation controller running a software-based FLISR solution (such as Blueframe DMS FLISR) using an industry-standard protocol.

This FLISR system’s wide-area visibility makes it possible to determine pre-fault system loading, observe safety and margin constraints, and determine the location of the fault (or faults). Using this information, it quickly determines which actions each recloser must take to successfully minimize the impact of the outage and restore power.

In the case of this event, the regional FLISR solution sends an open command to R2 and, once it is confirmed open, sends a close command to R3. It may also issue a Settings Group change command to R3 to allow it to properly coordinate with R5 and R4.

In more complex feeder topologies, software-based FLISR solutions can sectionalize an outage into multiple zones if necessary, using multiple restoration options to reach an optimal power restoration solution without violating any margin or safety constraints.

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Every SEL solution comes with the most reliable devices and best warranty in the electric power industry—plus free technical support for SEL products and systems.

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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No matter how long your SEL products have been in service, you’ll reach an SEL expert who can provide the service and support you need. SEL support teams are stationed in regional offices around the world and staffed with application engineers who are experts in our products and in power system applications.

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SEL support teams are stationed in regional offices around the world and staffed with application engineers who are experts in our products and in power system applications.

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