Electric utilities often employ an outage management system (OMS) to help them determine the location of a protective device that responded to a fault on their distribution system. Such a system can also help them prioritize restoration efforts based on the scope of the outage and the number of customers affected.
When a trouble call is received, the utility dispatches a crew to find the site of the problem. If the utility has SCADA capability, it may have an idea of the location, but not the exact fuse that blew or how far the fault was from the recloser that locked-out. Fault location and power restoration can take 20 minutes to several hours. Outage management after an area-wide storm often requires a great many utility crews and a large amount of material. Power restoration can take days or longer.
If most of the distribution system is still functional, a fault location, isolation, and service restoration (FLISR) system, integrated into the OMS, can restore power to unfaulted portions of a faulted line in seconds.
FLISR systems can use either a centralized intelligence or distributed intelligence architecture. Systems using distributed intelligence offer a key advantage in that they can still operate if there is a communication failure from devices in the field back to the utility’s central operations. With switching decisions made locally, FLISR systems using distributed intelligence can respond quickly; there’s no need to continually transmit data back to central operations and wait for instructions.
According to a 2006 Federal Energy Regulatory Commission report, less than 20 percent of the distribution feeders in the U.S. are automated in any manner. In most cases, implementation of a FLISR system requires the acquisition of equipment to provide sensing and automation of the lines. Several kinds of FLISR systems are available and each can locate and isolate faults without the need for a dispatcher or field crew, and can minimize the outage area by rerouting power. Some, however, can only handle a limited number of intelligent electronic devices (IEDs). Others can’t rebalance load after the system has been reconfigured. The location where restoration decisions are made by the FLISR can have a dramatic effect on the speed of restoration.
Centralized FLISR Systems
Centralized FLISR systems use SCADA-enabled switches and sensors located at key points in the distribution system to detect an outage, locate the faulted area, isolate the fault, and restore service to unfaulted areas. Some switching operations can be performed automatically depending on the capabilities of the IEDs and sectionalizing devices, and the speed of SCADA system communication. In many cases, the system only sends an alarm to the control center that must be acted upon by a dispatcher. Restoration can takes upwards of 20 minutes.
In a centralized FLISR system, secure, reliable two-way data communication and powerful central processing are essential. Point-to-point or point-to-multipoint communication is used with data collected in the distribution substations transmitted back to the FLISR system. The system individually polls each substation control and IED served by that substation and collects each response before issuing a restoration command. This arrangement is susceptible to a single-point of failure along the communication path. The addition of redundant communication paths is usually cost-prohibitive.
Centralized FLISR systems require a large amount of bandwidth to operate. The addition of devices on the system creates latency and increased restoration time as the system polls devices and collects data. A point-to-multi-point system can be easily overwhelmed and unable to process information sent from multiple field devices to the control center. So when the FLISR system is needed the most ¾ during a widespread storm, natural disaster, cyberattack, or period of high loading ¾ a centralized system is most likely to experience problems.
Centralized FLISR systems can also be the most costly and have the longest deployment time. They require time-consuming integration with the distribution management system (DMS), fine-tuning, and data scrubbing of the geographic information system (GIS) before they’re reliable. The higher the level of automation desired, the more logic needs to be programmed into the system, which can make future growth challenging. Further, integrating a centralized FLISR system with an existing DMS or SCADA control system can decrease valuable data processing power and bandwidth that’s needed for power flow analysis and supply balance.
Substation-Based FLISR Systems
Substation-based FLISR systems use main logic controls located at the distribution substations; these systems work with fault sensors and IEDs out on the feeders. A substation control center or “relay house” is typically required. Many of these systems can be integrated with substation-based capacitor control or volt/VAR optimization systems.
With substation-based FLISR systems, sizable load is dropped if substation breakers are used for fault interruption. If reclosers are used for fault interruption, the protection and sectionalization schemes of the IEDs must be resolved before the system can begin service restoration. When protection and sectionalization has been completed, the FLISR system polls the IEDs in much the same way as with a centralized system, collecting data on the status of each switch before issuing a restoration command.
Substation-based FLISR systems can take three to five minutes to restore power to unfaulted sections depending on the settings of the IEDs and the distance between the substation controls and the devices. A substation-based FLISR system can have a single point of failure: If main substation control communication fails, the entire system is off-line.
Unlike a centralized FLISR system, a substation-based system cannot be added to an existing DMS. If communication equipment, control power, and a control house are not already available at the substations, adding them can be prohibitively expensive. Substation-based FLISR systems can be complicated to set up, difficult to expand, and lengthy to implement, depending on the IEDs selected, communication, and desired extent of integration with an existing SCADA system.
Distributed-Intelligence FLISR Systems
FLISR systems with distributed intelligence and mesh networking are the simplest to configure and fastest to deploy. They can be readily integrated into an existing SCADA or distribution automation system too. These systems typically operate in seconds and can be set up with the ability to “self-heal”—re-route power and shed non-essential load under multi-contingency situations.
Distributed-intelligence FLISR systems offer a high degree of scalability as well. One or two automatic restoration points can be added at a troublesome location on a feeder or the entire distribution system ¾ from the substation on out ¾ can be automated with multiple sources and interconnections. Distributed-intelligence FLISR systems can be integrated with a variety of fault detection and sectionalization devices too and operate faster than centralized or substation-based FLISR systems. By starting with a few of these devices and increasing their numbers as requirements grow or as the budget allows, distributed-intelligence systems are the easiest to expand.
With mesh network communication, each device can communicate to and around one another. Redundancy is built into the communication paths, providing self-healing capability for the communication network if one or more members of the mesh become inoperable. Distributed-intelligence FLISR systems include safety features to prevent automated switching while crews are working on the feeders.
Unlike centralized FLISR systems, distributed-intelligence FLISR systems can be deployed without implementing a DMS or GIS. Extensive data scrubbing of an existing GIS isn’t needed and there’s no need for controls or a control house at the distribution substations. Though completely compatible with SCADA systems, distributed-intelligence FLISR systems don’t require a SCADA system to operate.
Distributed-intelligence FLISR systems require the deployment of IEDs out on the line. In many cases, the control software can be deployed on existing equipment through the addition of an interface control module. If a DMS is used, implementing a distributed-intelligence FLISR system will free up bandwidth and processing power to these systems, allowing them to provide power flow analysis and other functions that require more data, time, and data processing power.
Depending on the number of IEDs included in the system, a distributed-intelligence FLISR system can be up and running within a few days or weeks.
Example Results of Distributed-Intelligence FLISR System
The City of Chattanooga deployed a distributed-intelligence FLISR system to reduce the impact of power outages, which are estimated to have cost the community $100 million a year. On July 5, 2012, a severe storm came through the city, causing widespread power outages. The utility, EPB, realized a 55 percent reduction in duration outages experienced by their customers—about 90 percent of its fault detection and sectionalizing devices were programmed for automatic power restoration.
EPB estimated that they were able to restore power to all customers nearly 1.5 days earlier than would have been possible before implementing their FLISR system. The utility estimated that they saved roughly $1.4 million in restoration costs.
Implementation of a FLISR system typically involves a number of steps, including:
- a communication site survey to ensure acceptable signal strength between IEDs and the head-end SCADA radio, if applicable
- an overcurrent protective device coordination study to select appropriately rated protective devices and their settings
- determination of IED settings
- factory acceptance testing of the IED to verify the system will work with the utility’s specific protection settings, available fault currents, connected loads, etc.
- training of the utility’s personnel
- SCADA integration, if applicable
- commissioning of the system
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