Innovative Device Brings Fault-Testing to the Edge of the Grid, Improving Power System Reliability

S&C Electric Co., an employee-owned company with global headquarters in Chicago, Illinois, rolled out an innovative solution designed to mitigate nuisance outages for power customers located on the grid edge. The new VacuFuse II Self-Resetting Interrupter has the ability to test if a fault is temporary, and if so, it automatically restores power, eliminating the need for utility companies to roll trucks and send line workers to replace overhead distribution transformer fuses.

Not All Faults Are Created Equal

“The majority of overhead faults are temporary, so one of the most effective ways to manage them is by using fault-testing devices to keep temporary issues from becoming permanent outages,” Lea Mauer, S&C’s senior manager for Market Intelligence, said in a video released Monday to launch the new product. “Typically, fault-testing devices are deployed on the main feeder, but S&C has created the VacuFuse II Self-Resetting Interrupter, which brings fault testing all the way to the edge of the grid,” she said.

Some studies have shown that up to 70% of faults at the edge of the grid—areas typically protected by overhead distribution transformer fuses, which operate whether a fault is temporary or permanent—are caused by nuisance issues. Temporary faults are often caused by things such as foliage or wildlife that quickly clear; yet, power outages can last hours for customers in remote areas when fuses require replacement.

Customer Experiences Vary

One reliability metric that power companies commonly track is System Average Interruption Frequency Index (SAIFI). SAIFI measures the average number of times that a customer experiences an outage during the year. However, the SAIFI metric averages customer experiences across the whole system, so it can be misleading. Mauer explained that even if a utility company’s SAIFI is low, there could be outliers at the edge of the grid where an advanced protection device could make a big difference for customers.

“Outages at the edge of the grid are having a greater impact than ever before, and what’s tricky about these areas is that issues at the grid edge tend to cluster into pockets, meaning that some customers see outages several times per year,” she said. Using the VacuFuse II Self-Resetting Interrupter, utilities can target troublesome spots on the grid. S&C says power companies can lower their maintenance costs and keep customer satisfaction high with this new solution.

How the VacuFuse II Self-Resetting Interrupter Works

“When this device detects fault current, the vacuum interrupter inside the unit opens and interrupts that fault current,” Marshall Mauney, senior director for Overhead Lateral Automation with S&C, explained in a video demonstration. “About 45 seconds later, the interrupter will test the line to see if the fault remains. If the issue is temporary, then the vacuum interrupter remains closed and power is restored without the need for an expensive and costly truck roll.”

Standing in S&C’s product demonstration center in Chicago, Mauney also showed what happens when a more serious fault occurs. “What I’m going to do now is trigger a permanent fault,” he explained. “You could hear that the vacuum interrupter did open up. Now, it’s going to come back in about 20 seconds, and it’s going to close back in. It sees that the fault is still there, so now it’s locked out, and in a few seconds, it will drop open. This will leave the line crews with a visible marker to make it very, very easy to detect, find where the problem is, and repair it.”

The VacuFuse II Self-Resetting Interrupter works with overhead distribution transformers from 7.2 kV through 12.5 kV and is available in sizes compatible with 15-kV and 25-kV cutouts to accommodate most lateral systems. It weighs about 12 pounds, making it easy to install. The devices are factory-configured prior to shipping with standard curves (such as K, KS, and T), customizable curves, or S&C’s new transformer-specific curves.

“We work closely with our customers to understand their challenges and develop solutions for real-world applications,” Anders Sjoelin, president and CEO of S&C, said in a statement. “As utilities are facing a major energy transformation, they are looking for ways to modernize and improve reliability and resiliency in every part of the grid. The VacuFuse II Self-Resetting Interrupter is the latest example of how we’ve collaborated with customers to solve industry challenges and created an innovative, easy-to-use solution that tackles outages at the grid edge.”

—Aaron Larson is POWER’s executive editor (@AaronL_Power, @POWERmagazine).