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Fault Isolation Reconfiguration

Utilities have been looking to improve performance metrics as a means to meet regulations since the late 1990s. One of the most reliable ways to do so is to quickly determine the location of faults, isolate them, and automatically restore the healthy feeders promptly. G&W Electric has been installing Fault Detection, Isolation and Restoration (FDIR) systems for many years.

The main benefits of FDIR schemes include:

  • Shorter outage durations
  • Fewer sustained outages
  • Improved performance indices
  • Enhanced operational efficiencies
  • Improved service quality

G&W’s Lazer automation systems can isolate faults with the closest upstream device to allow the fewest number of circuits to see the outage. Our pre-configured solutions allow you a choice of fully distributed intelligence and peer-to-peer communications, local controllers built directly into the switches, or a combination of both. This flexibility coupled with standard communication interfaces and open protocols offer solutions that can meet almost any automation need including smart grid applications. Like all of our solutions, FDIR systems are fully tested at our facility before ever being shipped.

FDIR Configurations

Closed Loops – the fastest tripping option with fault isolation in as little as 6 cycles. Two sources are run in parallel with all switches in the loop closed. Closed loop solutions are excellent for Universities, military bases, or other locations that cannot afford to wait seconds for their power to return.

Open Loops – allow for fault isolation and restoration in 30 cycles to several seconds. Two sources are connected in a loop with one open point. Open loop solutions are excellent for most commercial and residential circuits, some industrial customers, and municipal customers.

Multi-Source Network – indicates greater than two sources feeding a circuit. These applications frequently involve more advanced algorithms like load flow and source prioritization. Multi-source networks solutions are excellent for local utility circuits, some campus environments, downtown circuits, and rural circuits.


Contact your local G&W representative to receive a complete review of your current project requirements and recommended G&W solution. Please click on one of the tabs below to review some of our customer installations.

A university required a substantial upgrade of their distribution system to accommodate plans for future load growth. Reliability was the main concern, so the goal of the project was to meet the following requirements: connect radial circuits into multi-source loops, isolate faults within 10 cycles, and permit the gathering of information to optimize power usage. G&W, along with Canada Power Products, helped design a new network comprised of ten closed loop circuits with eighteen radial circuits. A total of one hundred ten protective relays were added to new and existing equipment. Fiber optic cable was used for the protection scheme and SCADA communication. Each loop used an SEL 3351 processor as data concentrator for all of the relays. The data processors were connected to a Survalent master station that had access to all of the system information. The controls were then tied into two separate local area networks that extended between the substations and to the operations and engineering buildings. For more information: Application Guide

Closed Loop FDIR System

An expanding military base needed to install a new, automated loop system operating at 25kV (150kV BIL) with the ability to interrupt up to 25kA. The required configuration was a closed loop, communication assisted protection system using POTT and DCB schemes. In addition to the supplied system, the provider had to communicate with existing substation breakers.

G&W supplied the most economical solution using TNI gas insulated switchgear with internal potential transformers and a custom control package that integrated SEL-351S relays and fiber optic transceivers. Each switch also contained three internal power transformers to monitor voltage. The system was programmed and fully tested to provide minimal isolation time by tripping only the two interrupters closest to the fault.

For more information: Application Guide.

Open Loop Switching Fault Detection and Isolation

A capital improvement project was approved to upgrade the electrical system of a critical coastal evacuation bridge. The system was originally a 5 kV manual reconfiguration system and was to be changed to a 25 kV automated fault isolation system. This project presented several challenges including meeting tight space limitations, no disturbances on the changeover from manual to automatic, working with separate utilities at either side of the bridge and complete reconfiguration within 30 seconds.

G&W, along with Canada Power Products (CPP), supplied a solution that included 11 fully automated 27kV, RFI type switches connected in an open loop. Each switch had one or two SEL-351S relays that were used for protection and to act as an RTU for the included Survalent Master Station. Nine of the vault style switches were installed on the bridge structure with the other two acting as utility feeders on either shore. The system was set up in the factory and tested to verify operation.

For more information: Application Guide.

Open Loop Fault Isolation and Reconfiguration

A US military base was interested in improving the reliability of their underground distribution system. They wanted to install the project in two phases to allow for new substations to be built that would feed the distribution system. All switches would need to be automated and capable of detecting and isolating faults.

G&W worked with the military facility to provide a flexible system that used automated TNI style, fault interrupting switches. All switches were protected and monitored by SEL-451 relays. The first phase of the project was to install the switches into radial feeds and the second phase connected them into two open loops. All switches in each loop were connected to an SEL-2100 logic processor that controlled the reconfiguration. During a fault the closest switch would interrupt to protect the troubled line section. The logic processor would then open the switch on the other side of the faulted line section to isolate it and close the open point switch to restore power to the healthy line sections.

A recent flood caused an extended outage on a critical circuit feeding several important government buildings. The utility was asked to provide a solution to prevent the outage from happening again. This system needed the capability to isolate faults and reconfigure without communication to the substation circuit breaker. G&W provided a solution consisting of three fully automated 15kV switches. TVI style switches were used to fit the footprint of existing air switchgear pads. Each contained an SEL-451 relay which provided circuit protection as well as reconfiguration logic. Fault indicators were used on the line ways to determine the location of the fault. The three switches communicated to each other using MDS TransNET 900 serial radios. After a fault, the upstream breaker would open, wait approximately 10 seconds, and then close back into the system. During that time the switches would locate the fault and isolate it.

Automatic Fault Detection and Isolation with Controller

A municipal power provider needed to provide a new, key, industrial customer with reliable power during a circuit outage or fault. The solution had to interrupt faults and reconfigure in the shortest time possible because even brief outages could affect the customers’ processes. Two independent 38kV circuits were available.

G&W provided a solution pairing two Viper-ST reclosers, one on each 38kV circuit, and four 6-way PNI style switches with stored energy mechanisms. The reclosers were protected by SEL 651R relays and each switch had one SEL-451 relay and one SEL-751A relay. All relays were communicating with an SEL RTAC controller that was built into one of the switches and acted as the reconfiguration brains of the system. A fault on the system caused the recloser to trip, the RTAC to determine the location of the fault, open and close the correct switches to isolate the faulted line section, and finally close the recloser to energize the reconfigured circuit in less than one second. This operation was fully tested at the factory.

For more information: Application Guide.

Scalable Solid Dielectric Switching FDIR Loop

A utility was interested in improving service reliability by installing an underground fault detection, isolation, and restoration circuit to feed several important residential and commercial customers. They were interested in a solution that could be scalable from an individual switch to a full circuit of switches capable of performing an open loop restoration.

G&W Electric provided a system based on four-way, back to back Trident-SR solid dielectric switches. SEL-451 relays were used for the automation logic and source protection with SEL-751A relays on the load ways. Communication was through fiber optic cables. The relay logic was designed to be extremely flexible so the same program could be used in multiple scenarios without modification. By activating different parts of the program, it could be configured as a standard automatic transfer switch, as a through point automated loop switch where both line ways are normally closed, or an open point automated loop switch where one line way is normally open.

For more information: Application Guide.

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