No one ever said converting overhead (OH) facilities to underground (UG) was going to be easy. But with years of practice, Santee Cooper (South Carolina Public Service Authority; Moncks Corner, South Carolina, U.S.) is making the task seem much less daunting.

Over the last five years, the utility has put programs in place with several municipalities that provided a means for making a smooth transition. Supplying power to more than 1.8 million South Carolinians, Santee Cooper is a state-owned electric and water utility that has direct service to customers in three counties in the state and provides power to 20 of its electric cooperatives. To date, Santee Cooper has converted 42,800 ft (13,045 m) of main feeder and currently has an additional 25,200 ft (7681 m) of conversion projects in the design or construction phase.

The conversion process started several years ago when Santee Cooper began receiving an increasing number of requests from its municipalities to make the switch, especially in developed downtown areas. To accommodate these requests, the utility created a funding option for each municipality through franchise agreements. Santee Cooper currently has such agreements with the cities of Moncks Corner, Myrtle Beach, North Myrtle Beach, Conway and Loris.

In areas where these projects have been completed, municipalities and customers alike report a high level of satisfaction, indicating that the benefits of the end result overshadow the obvious inconveniences of a long-term construction project. Because of seasonal constraints associated with coastal distribution areas, the time line for converting a typical 1200-ft (366-m) stretch of Ocean Boulevard in Myrtle Beach is three years.

So, what is Santee Cooper's secret to success? Proper planning, design and execution — not to mention managing the countless project details — has helped the utility streamline its conversion process.

Identifying Key Players

Although each job is different, Santee Cooper had to devise a standard process for completing the conversions. The first step was to ensure that all stakeholders — typically Santee Cooper, the municipality, TV/telephone companies, property owners/leaseholders and construction contractors — are onboard. Coordination between all players is no small task. The municipalities have control over setting the priority and time line of the work. The TV/telephone companies must ensure designs for any conduit system will meet future needs. To prevent delays, property owners also must be involved. And contractors must fulfill all commitments made to stakeholders during construction.

Typically, certain construction constraints accompany each project dictated by its location. For example, jobs close to the ocean in Myrtle Beach and North Myrtle Beach typically affect hotels and businesses that see a peak in business during the summer months. To be sensitive to such needs, most construction phases of a conversion project are scheduled between the U.S.'s Labor Day (the first Monday in September) and Memorial Day (the last Monday in May).

Initial Design Work

The first year of a project consists of completing a detailed design and obtaining easements and any required encroachments or permits. Researching existing easements before designing and laying out the UG system is helpful. By identifying areas with existing easements or rights of way (R/W), a utility can minimize the number of new easements required. Santee Cooper also has the project area surveyed to update the GIS land base when necessary, typically when structures on private property need to be shown on the construction plans.

After this information is gathered, it is compiled in a CAD file. The new UG distribution system for the area is designed based on this CAD file. Having the locations of all known UG utilities and the existing hardscape allows for a more realistic placement of a new conduit system as well as the necessary vaults and enclosures. This step has been beneficial in reducing the number of change orders once the project is underway.

After a detailed design of the UG power system has been completed, which typically takes several months, it is shared with the local TV/telephone companies. Completing the design in this order — power and then communications — produces fewer redesigns than if each utility designed its system independently.

Acquiring Easements, Encroachments and Permits

After finishing the initial design phase, the municipality provides a general notice to the public. Next, the utility's R/W agents begin contacting property owners to request easements for equipment locations. This process can take anywhere from six months to one year. It's important to make sure that all commitments made to property owners during the easement acquisition process are included on the set of construction plans. These agreements can range from agreeing to work on properties during specific dates to requiring that the conduit system be directional bored.

After the majority of the easements are acquired and changes are reflected in the design, the utility applies for any necessary encroachments or permits, such as those associated with crossing under existing bodies of water. The municipalities typically coordinate obtaining such permits from the Army Corps of Engineers. In Santee Cooper's experience, each city has handled this task differently. Some use internal engineering work forces, others use contracted civil engineers. The cities typically coordinate the encroachment application for work to be done within any state or county R/W as well. This coordinated effort for permits and encroachments works better than each utility applying independently for a permit or encroachment.

Installing Conduit and UG Cable

Once all easements, encroachments and permits have been obtained, the contract for installing the UG conduit system goes out for bid. This usually takes place during the second year of the project. Each utility is responsible for inspecting the installation of its conduit system, while the city remains in control of the contract and restoration of any damaged hardscape.

The contractor is responsible for all conduit and for blowing strings through the installed conduit. This places the burden of verifying the integrity of the conduit system on the installing contractor, not the utility crews that will later pull cable through the system. Santee Cooper orders and provides the vaults and enclosures.

Unless otherwise noted in the contract, the contractor typically has the liberty of installing the conduit system via an open trench or by directional boring. On a typical installation, which has included 20-plus conduits, the open-trench method has proven more cost-effective because of the demolition required to sort through such a large conduit bank coupled with the increased cost of directional boring.

However, directional bores have been required in situations where the Department of Transportation's requirements for making perpendicular crossing under a R/W exist or when it's necessary to avoid conflicts with future drainage projects. In cases where it's necessary to cross main thoroughfares, boring reduces road cuts and the problems associated with patching in high-traffic areas. In instances where the utility is aware of a future drainage project, it instructs contractors to directional bore the conduit banks at a depth below that of the excavation required for future drainage in an area.

After installation of the conduit system is complete, Santee Cooper begins constructing the new UG distribution system. The UG cable is pulled in the new conduit system and terminated in the UG enclosures and vaults installed by the city's contractor. After the UG distribution system is installed, both the OH and UG systems are maintained until all services are converted over to the new UG system. This has been one of the more challenging areas of the entire conversion process. Although municipalities have taken the lead in notifying customers that their services will be converted from OH to UG, there are always a few OH services that are maintained from the new UG system to allow the OH primary to be removed in an area.

Overcoming Obstacles

After several years of practice, Santee Cooper has learned that each phase of a conversion project presents its own set of challenges. For example, one of the first jobs it took on was delayed one year because of miscommunication between the utility companies and the property owners within the limits of the conversion project. The UG distribution system that Santee Cooper had traditionally designed and installed up to this point consisted of UG cables with pad-mounted equipment (switchgear, enclosures and transformers). When the property owners were told about the OH-to-UG conversion project, they assumed UG cables and subsurface equipment would be used. After realizing the conflicting visions of a final product while acquiring easements, Santee Cooper was tasked with finding, evaluating and approving new equipment required to complete the conversion project in these developed downtown areas.

While researching subsurface equipment, Santee Cooper asked its operations department for input. This group recommended finding equipment that could be operated from above ground that would also provide an above-ground visual open. Santee Cooper found subsurface alternatives for 3-phase primary enclosures as well as switchgear for its distribution system.

The subsurface alternative for its primary enclosures was met by combining composite subsurface enclosures with standard four-position 15-kV loadbreak modules on stainless steel tilt-mount brackets. This allowed the enclosures to be installed in sidewalk and alleyway applications without impeding the property owner's use of the area. The operations department is also able to operate the 200-A elbows the same as in a traditional pad-mounted enclosure.

There also were concerns about possible lengthy outages in the event of a cable or equipment failure. To minimize the time required to track down fault locations, a UG radio fault indicator and drive-by remote system from Power Delivery Products (Alpharetta, Georgia, U.S.) was installed in all subsurface equipment. This allowed for the detection of tripped fault indicators without stopping and removing the covers at each subsurface equipment location.

To meet the operational requirements of being operable from above ground as well as providing a visual open above ground, S&C's Vista Undercover Distribution Switchgear was chosen. This particular switchgear is capable of operating while submerged underwater, which is critical in coastal installations. The Vista switches are installed in vaults built to specifications provided by S&C. The vaults are approximately 10 ft by 10 ft by 7 ft (3 m by 3 m by 1 m) with a weight of 24,000 lb (10,886 kg). The Vista switch is offered in many configurations with combinations of 600-A and 200-A compartments. This flexibility reduces the total number of switchgear required as compared to a design using the traditional PME-9, 10 and 11 pad-mounted switchgear.

Installing the large vaults required for S&C's Vista switchgear in developed downtown areas has not been completed without working through numerous conflicts, which range from relocating water and gas lines to removing 60-year-old fuel tanks.

For example, water and gas lines were in conflict with a vault installation on one project. Shifting the vault was not a viable option due to a mature live oak tree in the area. After consulting the municipality, Santee Cooper decided to have the water and gas lines relocated to save an existing live oak. This effort took several weeks to coordinate and delayed the vault installation.

The utility also has seen several instances where old fuel tanks were still in the ground. It also has encountered numerous old water and sewer lines that were not mapped as facilities were updated on GIS and CAD systems. As they come across these conflicts and relocate either the existing utility or adjust the new equipment locations, most municipalities have been taking these conversion projects as an opportunity to ensure that their as-builts of the area are as accurate as possible.

Another lesson Santee Cooper learned is that it's best to install large vaults and conduit connections early on in the project. This typically provides ample time to resolve any conflicts that arise during construction and the contractor can work in other areas without delaying the entire project.

As Santee Cooper completes more and more conversion projects, it continues to tweak best practices and learn from each new experience. The conversion from OH to UG is running smoother as all parties become more proficient at working together.

Brad Parnell is a general engineer with the System Improvements and Franchise Design Division of Santee Cooper. He has a BSEE degree from the University of South Carolina in Columbia, South Carolina, U.S., and an MBA degree from Winthrop University in Rock Hill, South Carolina. Parnell is a registered professional engineer. EBPARNEL@santeecooper.com