Considering all the hurricanes, tornadoes and ice storms that wreak havoc on America's electrical systems each year, it is no wonder many utilities have considered converting overhead lines to underground. However, most studies have come to the same conclusion — it is too expensive. Also, underground lines are harder to service.

Edmond Electric (Edmond, Oklahoma, U.S.), a municipally owned electric utility just north of Oklahoma City, faced many of these same challenges. Conversion appeared to be costly, and tearing up yards and streets in mature neighborhoods did not sit well with the community. Nevertheless, city officials decided the benefits of long-term improvements in system reliability, which ultimately have a positive affect on customer loyalty, outweighed the challenges of an overhead to underground conversion program.

Start Where the Need Is

Given the aging condition of some of the 96-year-old company's poles and facilities, the utility first identified areas already in need of repair and upgrade. By starting with an area that needed attention, some of the conversion expense could be absorbed in annual maintenance and upgrade costs already budgeted. A survey determined that the Henderson Hills district, a 50-year-old area, continually had high volumes of outages. Poles in the area were starting to rot, and structural damages from a recent ice storm still needed repair. Overgrown trees posed a perpetual encroachment, adding to outage problems. But when crews trimmed the trees back, some people in the neighborhood became upset.

Taking an incremental approach to converting overhead facilities has proven to be a win-win for residents and the city of Edmond. The Henderson Hills project was completed in July, converting nearly 500 residents to buried electric cable in conduit. The next project, which begins in September, will target a similarly sized neighborhood, Clegern Park Edition, where outages have been high and older equipment needs replacement and repairs.

Horizontal Directional Drilling

Key to the success of this project was the use of horizontal directional drilling (HDD) to install the conduit. Installation and restoration costs are the most expensive part of any underground job. In addition to the labor and equipment expense, open-cut installations cause disruption to the community, traffic problems and recurring sinking where ditches have been dug and streets have been cut. To avoid these “pit falls,” Edmond capitalized on advancements in both HDD equipment and technique, now available in the maturing industry.

Most significant in the advancement of HDD is the compactness of newer directional drills. Today's drill units are track-mounted and self-contained, which means drill pipe is carried on the drill unit, and is automatically loaded and unloaded in a cartridge-type mechanism. The power unit and built-in power steak-downs also are onboard, so crews can tram the unit to the drill site, set up equipment, and drill in a fraction of the time it use to take to carry out drill pipe and hook up hydraulic hoses. Self-contained units have a smaller footprint, which makes them easy to get into tight places, and the newer models are built with higher thrust and pullback capacities. Doyle Webb Inc. (Edmond), Edmond Electrics' alliance contractor, used several Ditch Witch self-contained units on the overhead to underground project, which sped the installations and cost less than open-cut.

For the service installations from the pedestal to house, a JT520 5000-lb (2268-kg) rig with 6-ft (1.8-m) drill rod was used. Its small footprint makes it easy to fit through a 36-inch (91-cm) yard gate. Two JT920s with 10,000-lb (4536-kg) pullback, a JT1720 and a new 1220 were used primarily for the parallel shots to install primary and secondary distribution pipes in the front easement. A total of more than 18,300 ft (5578 m) of conduit was installed using HDD. Very little was open-cut.

Hard as Rock

In rocky conditions, HDD traditionally has cost two to three times more per foot than drilling in soft formations. Some areas of Edmond, particularly the Henderson Hills subdivision, are notorious for harder formations and rock. The contractor used new “bear claw”-type bits with carbide-plated teeth, which negated the need for bringing in larger, more expensive, HDD drill units. In some cases, steering was a problem, but compared to the cost of renting mud motors and paying for a high volume of bentonite drilling fluids, the new bits paid off. Also, the physical size and weight of the larger rigs capable of steering in rock were not suited to this project. It is not practical to drive a 30,000 or 40,000-lb (13,607 or 18,143-kg) rig onto a driveway approach or front yard.

Another advancement in HDD that contributed to the success of the project was the growing knowledge of drilling fluids and selection of tooling. A few years ago, it was not uncommon to get stuck and have periodic bore failures. These factors had to be added into the overall cost of the bore. Bore failures on the job were almost nonexistent. Doyle Webb Inc.'s seasoned operators incorporated some of the industry's new HDD guidelines, which resulted in more accurate drilling. Making more successful bores each day translated into higher production and pinpointed placement of conduit.

Designed for Accessibility

The design called for the new underground facilities to be moved to front-yard easements. The underground cable was encased in high-density polyethylene (HDPE) schedule-40 conduit that could be readily accessed on trouble calls. These decisions were major factors in the acceptance of the overhead to underground conversion.

For most of the project, cable was installed in 3-inch (7.6-cm) HDPE conduit, except for one area of three-phase line where 4-inch (10-cm) pipe was used. In many cases, two to three conduits were bundled and installed in one borehole. Edmond's contractor personnel installed conduit, wire, pedestals and transformer pads. Electricians were required to change out the meter bases at the house. Edmond Electric linemen made connections and energized the new electric cable. The conversion design also included redundancy and loop-fed capabilities to all equipment. In the case of a cut line or cable failure, power can be rerouted to restore service quickly.

The accessibility strategy for ease of maintenance and repair has already been tested and confirmed. Last spring, a fault in one of the new secondary lines, possibly caused by a manufacturer defect in the new cable, was isolated, the wire was pulled and replaced in less than 30 minutes, mainly due to the new all-conduit encasement design.

Communications

Edmond Electric discovered the importance of quickly responding to questions and problems before they became serious concerns. A public education specialist worked throughout the two-year project hanging door hangers, answering phone calls and educating the neighborhood on the advantage of having underground lines and what to do when directional drilling rigs began showing up on their street. When customers heard about the increased reliability and the reduced exposure during storms, they became enthusiastic about the project.

Community meetings helped keep people informed about the Henderson Hills project. More than 100 citizens attended the first meeting, where the project was explained and the benefits to the community were presented. Edmond described directional drilling and what to expect during the conversion project. Several of Doyle Webb Inc.'s personnel attended the meeting. Area electric contractors were consulted for discussion of the residents' responsibility for meter-base change-out, wiring and estimated cost. Citizens were given the opportunity to express their feelings and ask questions.

Local Factors

Companies considering an over-head-to-underground program should understand the local factors that contributed to the success of the Edmond Electric project. Edmond is known as a “bedroom community” to neighboring Oklahoma City, where residents appreciate their trees and the quality of life. Citizens are all for seeing the lines and poles disappear. Edmond is also located in what is commonly referred to as “tornado alley” and is just far enough north to get ice storms.

A not-so-obvious factor has been the contractor, a lifelong resident of Edmond, with a 20-year history of working for the utility. Because they are local, they have placed a high priority on service to the customer, which was helpful when two or three crews with approximately three to six personnel each converged on a neighborhood all at once.

Next Time

The cost of the meter base installation is one wrinkle still being ironed out. On the Henderson Hills project, residents had to obtain their own electrician and pay for converting their meter base from overhead risers to an underground line. Of the just under 500 residents, 250 chose not to pay the extra $400 average cost. Although the lines were still taken underground, shorter poles were installed to accommodate customers who chose not to pay for the new meter base conversion.

Edmond Electric is researching the possibility of paying for the meter-base conversions in its next project. To secure a best price and a more uniform procedure, it plans to solicit bids from a single-source electrician who would install all meter bases. The added expense may be justified in eliminating the cost of the short poles, which were necessary where residents declined, and the logistics problem of waiting on third-party electrical contractors to complete their piece of the conversion.

Other utilities impacted by the conversion program were not prepared for the relocation of their facilities and the extra manpower needed to monitor excavation. For the next project, more time is being devoted to working with the other utilities in the area. With sufficient notice, cable and phone companies may take advantage of the opportunity to joint-bore in some areas, sharing the cost of bundling two conduits in one directional bore hole.

Conclusion

Converting overhead facilities fits with Edmond Electric's goal of providing high-quality electric service to its customers. Edmond is taking a one-section-at-a-time approach, budgeting to convert about 250 homes a year, beginning with the areas where repair dollars are already needed. Using directional drilling, higher-than-expected production with minimal restoration cost has been realized, setting a precedent for future projects. The city council has approved a revised budget line item for overhead to underground conversion, showing approval by increasing it from $500,000 to $750,000 a year for the next five years.

The community's response to directional drilling has been a welcome surprise. When residents first spied the door hangers, many expected dirt piles and torn up lawns. However, on some occasions, the conduit installation was completed between the time residents left for work and returned home. A councilman living in the area at first chose not to pay for the meter base conversion. After he saw the efficiencies of directional drilling, he became a convert as well as an advocate.

Dean Sherrick has worked for Edmond Electric (Edmond, Oklahoma) for more than 28 years. In addition to overseeing the overhead to underground conversion, as distribution superintendent, he is responsible for all field operations and maintenance activities plus administrative issues that affect Edmond Electric and the city of Edmond. He is a member of the Oklahoma Electric Superintendents Association and participates in Edmond's Strategic Business Planning Team, Work Practices Review Team, and other city tasks forces and committees.
Dean.Sherrick@ci.edmond.ok