Every time power goes out, a clock starts ticking. For electric utilities, that clock has a name — SAIDI (System Average Interruption Duration Index) and SAIFI (System Average Interruption Frequency Index). These two numbers sit at the heart of reliability reporting, regulatory compliance, and customer satisfaction. Yet for many distribution utilities, cutting them down feels like chasing a moving target.
The good news: the technology that can genuinely move these numbers exists. The less comfortable truth is that most utilities are still spending the majority of their outage time on activities that smart equipment and software can eliminate — namely, finding the fault.
What SAIDI and SAIFI actually measure
Before diving into solutions, it's worth being precise about what these KPIs capture.
SAIDI measures the total duration of interruptions experienced by the average customer over a given period, typically a year. It is expressed in minutes (or hours) per customer. A SAIDI of 90 minutes means the average customer experienced 90 minutes without power over the year.
SAIFI counts how many times that same average customer lost power during the period. A SAIFI of 1.2 means the average customer had 1.2 interruption events per year.
A third metric often tracked alongside them is CAIDI (Customer Average Interruption Duration Index), which equals SAIDI divided by SAIFI — essentially the average length of each individual outage. CAIDI is particularly useful because it reflects how quickly your crews restore power once an outage begins, independent of how often faults occur.
All three are directly impacted by one critical variable: how fast you can find a fault and isolate it.
Where outage time actually goes
When a fault occurs on a medium-voltage overhead line, restoration time typically breaks down into three phases:
- Detection — recognizing that an outage has occurred and which feeder is affected. With modern SCADA, this is usually fast.
- Fault location — identifying which section of the line or cable is faulted. This is historically where most time is lost.
- Isolation and restoration — switching out the faulted section and restoring supply to unaffected customers.
In networks without fault location equipment, field crews must physically patrol the line — sometimes tens of kilometers — to find a downed wire or damaged insulator. Depending on terrain, weather, and time of the day, this patrol can take anywhere from one to several hours. During this entire time, SAIDI is accumulating.
Deploying fault passage indicators, feeder monitors, and automated switching equipment directly compresses phases two and three. The goal is to arrive at the fault location, not search for it.
Layer 1: fault Indicators on the line
The first and most impactful layer in any fault location strategy is placing overhead line fault indicators at strategic points along the feeder — at section boundaries, branch points, and laterals.
When a short circuit or earth fault occurs, current flows from the source toward the fault. Every fault indicator the fault current passes through is "tripped" — it registers the event. The last tripped indicator before the first untripped one marks the faulted section. Operators receive this information in real time, without any patrol.
ATRIY's Lodestar series of overhead line fault indicators for 6–70 kV lines work on exactly this principle. They clamp directly onto live conductors — no outage needed for installation — and continuously monitor line conditions. The moment a fault current is detected, the device registers the event and transmits it via 3G/4G to SCADA. Control room operators see, in real time, which section the fault is in.
For networks where indicators need to be mounted at pole level rather than directly on the conductor, pole-mounted fault indicators such as the Lodestar PL10 provide the same detection capability using an electromagnetic flag mechanism, suitable for 1–36 kV distribution networks.
For transmission-level overhead lines operating at higher voltages, fault indicators designed for high-voltage lines extend this approach further up the voltage hierarchy.
What this does to SAIDI
The reduction of fault location time is the most direct and measurable impact. Instead of a crew spending two hours patrolling a 30 km feeder, the control room narrows the fault to a 2–3 km section in seconds. Crew dispatch is targeted. Restoration begins sooner. SAIDI shrinks.
Layer 2: feeder monitors at the substation
Fault indicators on the line tell you where the fault current passed. Feeder monitors at the substation tell you which feeder was affected, what the fault current magnitude was, the time of occurrence, and a precise set of electrical parameters at the source end — all of which support faster decision-making and more accurate root-cause analysis.
ATRIY's feeder monitors — including the Lodestar FM, FM-CS, FM-CS2, FM-FL, and FM-DFI models — are designed for substation panel installation and integrate with existing SCADA infrastructure. They continuously measure current, voltage, frequency, and load status per phase, and they detect both short-circuit and earth fault events. The combination of substation-level data from feeder monitors and field-level data from line fault indicators gives control room operators a complete picture.
This data layer also supports longer-term reliability improvement. Repeated fault events on specific sections can be identified from historical logs, allowing predictive maintenance to address chronic weak points before they cause the next outage — moving from reactive to proactive grid management.
Layer 3: automated switching — where SAIFI starts to fall
Reducing SAIDI requires finding faults faster. Reducing SAIFI requires preventing some interruptions from reaching customers at all, and restoring supply to unaffected sections without waiting for crew intervention.
This is the role of automated switching equipment on the overhead line: reclosers, load break switches, and intelligent disconnectors.
Reclosers: clearing transient faults automatically
Industry experience consistently suggests the majority of faults on overhead lines are transient: a tree branch briefly contacts the conductor, a lightning strike causes a flashover, a bird causes a momentary short circuit. If the circuit is interrupted and then reclosed after a short delay, the fault has usually cleared on its own and power is restored without any crew involvement.
A recloser is an automatic circuit breaker installed on the line that does exactly this. It interrupts the fault, waits, and recloses. If the fault has cleared, supply is restored. If the fault persists, the recloser locks out and isolates the section.
ATRIY's IDD-VCR vacuum recloser is rated for 10 kV / 630 A with a breaking current of 12.5 kA. Its standard auto-reclosing cycle is O–0.1s–C–O–1s–C (open, pause, close, open again if fault persists, pause, close). It operates in radial, open-loop ring, and closed-loop ring networks with dual power supply configurations. Protection functions comply with ANSI-50 and ANSI-51 standards, and communication uses IEC 60870-5-104 and IEC 61850-8-1 protocols for SCADA integration.
Each transient fault that a recloser clears without a sustained interruption is a fault that never contributes to SAIFI. This is perhaps the single most effective way to move that number.
Intelligent Disconnectors and Load Break Switches: Isolating and Rerouting
When a fault is permanent, the focus shifts to isolating the faulted section as quickly as possible and restoring supply to all customers not directly connected to it. In a feeder with multiple section switches, an automated system can open the switch immediately upstream of the fault and close a normally-open tie switch to restore supply from an alternate source — all without waiting for a crew.
ATRIY's Intelligent Disconnector IDD and Load Break Switch IDD-CB form the field-level automation layer that makes this possible. Working together with fault indicator data and the central software platform, they enable automatic or semi-automatic fault isolation and supply restoration.
Layer 4: software — making the system work together
Individual devices solve individual problems. A fault management software platform turns the whole system into a coordinated solution — correlating events across devices, visualizing the fault location on a network map, and supporting FLISR (Fault Location, Isolation, and Service Restoration) workflows.
ATRIY's fault management software aggregates signals from line fault indicators, feeder monitors, and switching devices into a single operational picture. Operators see the fault section highlighted on the network diagram, know which customers are affected, and can initiate restoration steps directly from the interface. The monitoring and control software extends this to broader grid control and long-term data analysis.
Communication units are the backbone connecting field devices to the software layer, transmitting event data reliably over cellular or other available channels.
The cable side: completing the picture
Overhead lines aren't the only part of the distribution network where faults hide. Underground cables, particularly in urban environments, present their own fault location challenges — and their own contribution to SAIDI when repair crews spend hours narrowing down the fault position in a cable that can be hundreds of meters long.
Cable fault locators and detectors address this segment of the network, applying time-domain reflectometry and other techniques to pinpoint faults in underground cables quickly, reducing excavation to the minimum necessary.
Short-circuit and earth fault indicators: substation and switchgear applications
In switchgear rooms and ring main units, short-circuit and earth fault indicators serve the same conceptual function as overhead line fault indicators — flagging which section carries the fault current — but in an indoor or enclosed switchgear environment. Combined with the outdoor line system, they give complete coverage from the substation busbar out to the end of the feeder.
A layered approach: matching solutions to network priorities
No single device solves SAIDI and SAIFI. What works is a layered approach, matched to the specific characteristics of the network:
Networks with long rural feeders and patrol-heavy fault location benefit most immediately from overhead line fault indicators with remote communication. The patrol is replaced by a targeted dispatch.
Networks with a high proportion of transient faults — common in areas with heavy vegetation or frequent lightning — see the largest SAIFI improvement from reclosers. Many transient faults that currently cause sustained interruptions simply clear on reclose.
Networks with meshed or ring topologies benefit most from intelligent switching combined with fault management software, enabling automated FLISR to restore unaffected customers within seconds of isolation.
Utilities facing regulatory pressure on reliability metrics benefit from the full stack: indicators for fault location speed, automated switching for restoration speed, feeder monitors for data completeness, and software for audit-ready event records.
Getting started
Implementing fault location and automation equipment does not require a network-wide deployment from day one. Many utilities start by installing equipment on the highest-priority feeders — those with the worst SAIDI history or the most customers affected — and expand from there as results have demonstrated.
Installation and configuration services are part of the solution: getting devices commissioned correctly, integrated with existing SCADA infrastructure, and calibrated to the network's fault current levels determines whether the investment delivers on its promise.
The underlying logic is straightforward. SAIDI and SAIFI are driven by how long faults go undetected and how slowly sections are restored. The equipment that eliminates those two delays — fault indicators, feeder monitors, reclosers, automated switches, and fault management software — is available, proven, and deployable on live networks. The question is not whether it works. The question is which feeders to start with.
ATRIY designs and manufactures fault location and distribution automation equipment for medium-voltage overhead and underground networks. The Lodestar product family covers overhead line fault indicators from 6 kV to high-voltage levels, feeder monitors for substation installation, automated switching equipment, and supporting software platforms.