Faulted Circuit Indicators

Risk Reduction Category

Grid monitoring

Technology Description

When a fault occurs on a line, crews are typically dispatched to the general area of the fault based on customers reporting outages. Line crews patrol lines visually, looking for interference from fallen trees, vehicular accident, and so forth. Finding the fault consumes time and cost to the utility. While technology exists to estimate the distance to a fault by analyzing signals being injected into the system, this type of fault location on distribution circuits has a number of challenges such as:

• Non-homogenous circuits (conductor sizes vary; often even along ‘main line’)
• Large number of laterals
• Typically, waveforms exist only at a substation breaker
• Impact of fault resistance on the measuement
• Evolving faults and conductor slapping
• Distributed Generation - fault location becomes more challenging with increasing levels of DG penetration
  • Synchronous generators can provide up to 5pu short circuit current
  • Three-phase inverters can provide 1.0-1.6pu positive sequence current during faults, negative sequence current less than 10%
  • Single-phase inverters may provide up to 2.5pu current during faults
• Grounding Practices
  • No impact on faults not involving ground
  • Solidly grounded: Enough ground current for fault location
  • Grounding through impedance: Faults currents lower than load currents
  • Ungrounded: First ground fault cannot be easily detected and located

Line fault indicators, or fault current indicators (FCI) simply clamp onto an overhead conductor and monitor the current through the conductor. If the peak current detected is consistent with a fault (to be distinguished from inrush current), then typically a visual indicator will illuminate or flash. The idea is that these simple, cost-effective, and self-powered indicators provide a visual aid to help line crews to quickly identify the location of a fault as they patrol the lines. By decreasing the amount of time it takes to located faults on the distribution system the utility can more quickly address any fires, with appropriate governmental entities (fire departments, forest service fire crews, etc). Key to the success of such a strategy involves optimizing the number and placement of FCI devices. This are most helpful in areas where other methods of fault location are ineffective or do not exist.

One factor to keep in mind is the effectiveness of FCI when another wildfire mitigation strategy is also in use. An example is a current limiting fuse, which may interfere with the ability of the FCI to detect a fault.

Fault indicators are available with varying capabilities. Table 1 shows some of those capabilities.

Technical Readiness (Commercial Availability)

Fault current indicators are not a new technology, but an option for utilities possibly to improve their response time after a fault. Improved fault location is important from a wildfire perspective, as crews can arrive at the location of the fault sooner and service or contain hazardous conditions. Basic and advanced faulted circuit indicators are available from a number of vendors at the present time. FCI are a mature technology.

The following list of manufacturers is the product of an Internet search using a general description of the technology as the search term. Sometimes more than one variation on the search term is used. The objective is to identify the most demonstration-ready products available in the category. Toward assessing demonstration readiness, the manufacturer websites typically provide useful information such as writeups of successful use cases or field demonstrations, number of deployments, or other indicators. Where lack of information exists online, further inquiry is made by phone. Generally, one to three frontrunners emerge as being most ready for a field demonstration. Preference is given to manufacturers who sell to the United States, or, if emerging technology, those who have participated in US-based field demonstrations.

Looking specifically at the Line Sensor/Smart FCI grouping, the following vendors have solutions for overhead construction:

• Without waveform capture
  • Aclara Technologies - https://www.aclara.com/products-and-services/sensors-and- controls/gridmonitoring-platform/mv-sensor
  • CNI Guard - https://www.cniguard.com/products/overline/ Four-Faith Smart Power - https://en.four-faith.net/Overhead-Line-Fault-Indicator/
  • SEL - https://selinc.com/products/distribution/fault-indicators/overhead-fault-location/
  • Eaton - https://www.eaton.com/content/dam/eaton/products/medium-voltage-power-distribution-control-systems/line-installation-and-protective-equipment/faulted-circuit-ndicator-application-guide-ca320001en.pdf
• With waveform capture
  • InHand Networks - https://www.inhandnetworks.com/solutions/overheadline- monitoring.html
  • Sentient Energy - https://www.sentientenergy.com/products/mm3-line-sensor

Implementations / Deployments

Fault Location Using Fault Sensors by Elektro (Brazilian utility):

• Use Intelligent Fault Sensors that communicate status back to the Distribution Operation Center (DOC)
• Communication takes place over a satellite network where 2G/3G coverage is limited/unreliable
• Due consideration was needed to make sure devices would stay powered to reliably communicate with the DOC
• The pilot project reduced fault location time by 50% and total outage time by 10%

A large number of US-based utilities have deployments of basic and advanced line fault indicators.

Innovations as of Mid 2023

Potential Enrichment Work Opportunity

References

Utility Experience and Novel Technologies for Distribution Grid Event Analysis and Fault Location. EPRI, Palo Alto, CA: 2022. 3002024378.