Trouble Spots in Your Distribution System?

Authors: Shankar V. Achanta and Steve T. Watt, Schweitzer Engineering Laboratories, Inc., USA

An affordable add-on can help your recloser control improve reliability

Some feeders need special attention, such as those with both underground and overhead lines or those with multiple taps on the line, some of which you might want to handle differently from the others. Maybe the line serves a critical load, so it makes sense to do everything possible to avoid a permanent fault. Or maybe there are some areas that don’t have fuses, and waiting for a nonexistent fuse to burn before reclosing would allow time to elapse and more damage to occur. These are the types of situations where even the best recloser control could benefit from additional information about the feeder.
Even in these challenging situations, you probably don’t need to replace your recloser control. The solution can actually be as simple as adding a new class of device to your system-an add-on to the recloser control that acts as the IED’s personal assistant.

Fault Location, Isolation, and Service Restoration
Utilities design fault location, isolation, and service restoration (FLISR) systems to improve system reliability. FLISR systems use communications-assisted distribution automation schemes to quickly detect and locate faults, isolate faulted feeder sections, and restore power to healthy sections of the feeder while crews repair the faulted section. With recent advancements in field devices, more and more of the parts of FLISR are becoming automated. This automation reduces human error and enables utilities to restore service in seconds instead of hours, thereby improving distribution reliability.
Faulted circuit indicators (FCIs) play a key role in speeding up service restoration to faulted sections after protective relays clear a fault and automation schemes restore service to unfaulted sections. Traditional FCIs typically consist of a sensor that monitors current on power lines and a visual target (mechanical or LED) that changes state when the current exceeds a predefined value. Line crews patrolling the line look for these visual indicators to track down the faulted segment.

Recently, FCIs with communications capabilities have become more common. These FCIs employ wireless communication to send fault information to SCADA or an outage management system to help line crews locate faults and restore service. Both traditional and wireless FCIs detect faults faster than protective relays clear the faults, but they indicate the fault condition at slower speeds. This is acceptable, because line crews do not require high-speed fault communication. They retrieve fault information through SCADA or the outage management system well after the protective relays have cleared the faults and the automation scheme has restored service to unfaulted segments of the line. The line crews use FCIs to physically locate the faulted segments of the line for restoring service to customers.
Both traditional and wireless FCIs improve Customer Average Interruption Duration Index (CAIDI) values for utilities because they reduce the patrol time for the line crews to pinpoint faults, thereby speeding up restoration and reducing customer outage minutes. However, wireless FCIs further reduce the patrol time by sending information such as the GPS location of the fault and the type of fault (momentary or permanent), thereby improving CAIDI. Figure1 compares the FLISR timelines of traditional and wireless FCIs, with the fault inception as the starting point

The next section of this article describes a new type of high-speed fault sensor that detects faults fast and communicates fault information to the protective relay or recloser control while the fault is still active to influence protection schemes. This new device not only improves CAIDI for permanent faults but can also enable utilities to mix protection schemes to optimize System Average Interruption Duration Index (SAIDI) and Momentary Average Interruption Frequency Index (MAIFI) values.

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