There are thousands of cities and towns throughout the country that claim to be committed to protecting their environment and natural surroundings. Sleepy Hollow, a quaint village in Kane County, Ill., is more committed than most.
This fierce commitment stems directly from the village’s origins. Floyd T. Falese, who bought a piece of land known as Sleepy Hollow Farm in 1953, retained the services of a prominent planner and landscape architect, Raymond W. Hazekamp, to create the village by laying out a “pattern of meandering roads, without curbs or sidewalks, that wound into curvilinear cul-de-sacs.” Having been instructed by Falese to retain the rural charm and natural contour of the location, Hazekamp, amazingly, accomplished his task without destroying a single tree.
It’s understandable, then, that the residents of Sleepy Hollow continue to treat the trees that line the streets and roads of this two-square-mile rural community almost like members of their own families. Consequently, when a problem arose in 2006 with a 5,000-foot stretch of power lines along Sleepy Hollow Road, the prospect of trimming back some of the tree branches as a potential solution was not an attractive one.
“We had an ongoing problem with an overhead circuit that runs through the center of town,” said Jack Mehrtens, director of distribution engineering and design for Commonwealth Edison (ComEd), which serves more than 3.8 million electricity customers in Northern Illinois, including Sleepy Hollow. “The issue was poor reliability, as a result of vegetation issues”.
“Our lines were installed along the road but were overhung by a canopy of trees,” said Mehrtens. “The people of the village are very proud of this main corridor of Sleepy Hollow Road, and in particular with the trees that line this road. So when we approached them about the issue, they certainly wanted to improve reliability, but they wanted to know what other options existed other than removing the trees.”
ComEd suggested a few different solutions. Placing the power lines underground was one such proposal, but this would have proven extremely cost-prohibitive. Total relocation of the lines was also brought up but was dismissed as well, primarily because it would have been a near-impossible task given the geography of the area and the overall system configuration. Sectionalizing was also considered, but was not applicable in this situation.
While ComEd works hard to collaborate with all customers and municipalities to ensure reliable service in a cost-effective manner, an acceptable solution to all parties was urgently desired. After all, ComEd, a unit of Chicago-based Exelon Corporation, one of the nation’s largest electric utilities, was responsible for more than 78,000 miles of power lines and ComEd was devoting a lot of time and attention to this one troublesome stretch.
“We had an area where we had a known reliability problem, and we were running out of options to improve the situation,” he said. “To make matters worse, this particular line not only served the town of Sleepy Hollow, but it also provided power to hundreds of customers outside of the town.”
Finally, another option presented itself. ComEd contacted Hendrix Wire & Cable, a provider of overhead and underground power distribution products, and investigated the viability of Hendrix’s spacer cable product for this application.
The case for spacer cable was compelling. Aerial spacer cable construction consists of high-strength, messenger supporting covered conductors in a close triangular configuration. It has the mechanical strength to weather severe storms and the electrical strength to prevent faults caused by phase-to-ground or phase-to-phase contact, tree contact or animal contact. The compact configuration and covered conductors can tolerate momentary tree contact, which allows trees to grow much closer to the circuit before tree maintenance is required. Ultimately, spacer cable can greatly reduce power outages caused by various elements in the environment and would require far less tree trimming — a huge benefit in solving the Sleepy Hollow dilemma.
“Hendrix spacer cable seemed to present a solution that appeared acceptable from a reliability improvement standpoint, but also to the village,” said Mehrtens. “We would have to do minimal trimming in order to get the facilities installed. Hendrix also seemed confident that we would be able to utilize most of the facilities already in place, so both the amount of work and associated cost were in an acceptable range.”
Given the importance of the project and residents’ concern for area trees, ComEd felt it was important to share its novel approach. Accordingly, ComEd staged a number of meetings with village officials and citizens, detailing the reliability and tree benefits of this approach.
After deciding to go the Hendrix spacer cable route — and informing by mail residents in the installation area — Hendrix’s Bob Biddle also traveled to Sleepy Hollow several times to address various aspects of the project such as: determining what could be done to minimize the amount of new equipment that needed to be installed; assisting in the design phase; training the contractors who would actually install the product; and being on site to ensure that the work was executed properly.
Hendrix’s expertise was also on display when it came to devising a plan for pole replacement. ComEd’s design scheme called for replacing each of the 24 poles along the nearly one-mile circuit. Hendrix, however, was able to modify the design; essentially, calling for replacement of every other pole and not attaching to the intermediate poles, which were topped at the secondary level after the open wire primary was removed. This allowed for the replacement of only 12 poles, just half of what had originally been envisioned.
The final version of the design was completed at the beginning of April 2007, and construction was completed at the end of June 2007, with Hendrix ensuring that all appropriate safety and performance standards were meticulously followed.
The project was a success, and that success is quantifiable. The most telling statistics are two measurements of reliability commonly used by electric power utilities: System Average Interruption Frequency Index (SAIFI) and Customer Average Interruption Duration Index (CAIDI). SAIFI is the average number of interruptions that a customer would experience, and is calculated in units of interruptions per customer, usually over the course of a year. CAIDI gives the average outage duration that any given customer would experience, measured in units of time.
Both SAIFI and CAIDI post-installation statistics improved. (The SAIFI and CAIDI numbers only refer to outages in the area that the spacer cable was installed; they do not include other outages on the feeder or in the town that are unrelated to the spacer cable installation.)
While it’s not easy to provide an exact number of dollar savings using the Hendrix design over the ComEd version, Mehrtens estimated that approximately $7,000 in material and $16,000 in contract labor savings were realized.
The spacer cable system has also performed well under fire. Since the installation, a fierce storm affected hundreds of thousands of customers in the ComEd service territory, and despite the storm’s severity and its impact on the lines close by, the rebuilt circuit using Hendrix spacer cable was unaffected; a few lone branches lying across the wires were the only remnants of the event.