In March of 2015, the backup to a main circuit that feeds power to 18,000 residents of Allentown, Pennsylvania, failed. The failure in the redundant circuit, which happened beneath the busy streets of the city, required an immediate and rapid long-term solution. Without the backup, failure of the main feed powering the congested 20 block area could leave tens of thousands of residents and businesses in the dark for an extended time.
The local utility found the failure in one phase of a vintage 1971 Phelps Dodge XLPE cable that extended 7,400 linear feet from the city’s Sumner Substation to the Central Allentown Substation. Because of its age and condition, the utility determined the 40-plus year old cable was unreliable and that the entire span should be replaced to ensure long-term reliability. To ensure the utility could effectively handle peak summer load requirements, they set a July 4th deadline for installation and activation of the new backup circuit.
|To safely access each manhole, the team closed sidewalks to pedestrian traffic, rerouting foot traffic to the opposite side of the street.|
To complete this large, complex and time-sensitive project, the utility decided to hire a qualified contractor to coordinate removal of the existing backup circuit and installation of three phases of replacement cable. After searching for and interviewing several firms, the utility chose to contract with Kerite. A division of Marmon Utilities, Kerite had more than 25 years of experience engineering and installing 46 kV to 138 kV high voltage cabling projects including substation and capacitor bank installations, urban high voltage feeds, subsea cable installations, river/bridge crossings, airport runway crossings and other complicated projects.
Kerite began to remove the failed cable on May 14. Before the existing circuit could be removed, an asbestos abatement crew entered each of the six manholes on the 1.4-mile route to remove asbestos tape that had been used to cover the splices on each phase. To safely access each manhole, the team closed sidewalks to pedestrian traffic, rerouting foot traffic to the opposite side of the street. Traffic management required several barricades, special signage and the assistance of a traffic control crew.
|Direct-buried cable in the highly-congested Sumner Substation.|
A total of 22,230 linear feet of vintage cable was removed. Once the Phelps Dodge cable was cleared away, the contractor systematically pulled six phases of 1500 KCMIL (91) CU, 138Kv SPS 850 MIL Kerite EPR cable to connect the two substations. Measuring 3.72 inches in diameter, each phase of the cable was spliced to the next phase inside the manholes. Each splice required 10 to 12 man hours from the installation team. Kerite workers also installed 15 PMJ 138 kV joints from G&W Electric and installed a 96-strand fiber optic cable for future telecom use. Once the new cable was in place, the team pulled out the old XLPE cable for each phase.
Because dirt and debris can compromise the long-term reliability of a splice, the contractor had to keep the work area and the new cable clean and uncontaminated. Moisture can also jeopardize critical electrical connections at 138 kV, so the air in the work area needed to be humidity-free-a challenge during hot summer months.
|New splice installed in manhole.|
To ensure ideal working conditions for splicing and installation in each manhole, Kerite staff covered the floors with protective polypanels that separated the work area from any existing contaminants on the floor of the manhole. To create a pristine environment for splicing operations, the team installed temporary air conditioning units and gas monitors that fed into the manholes. This allowed the team to control the extreme heat and humidity in the tiny, underground spaces and helped ensure the long-term effectiveness of the connections.
While the Kerite team removed and replaced the 18 sections of old cable and worked inside the six manholes, a second sub-contractor hired by Kerite, Central Connecticut Cable Co. Inc., worked at the Sumner Substation to hydro-excavate a 70-foot section of damaged cable that had been direct-buried. Once the old XLPE cable was removed, the sub-contractor installed a new concrete-encased duct bank in the same location where the old cable had been. Installation of the concrete duct bank was critical because the Sumner Substation was highly congested with no real estate available for new cable installations. With the duct bank completed, Kerite took over substation work, pulling the 138 kV cable through the newly installed duct bank.
|Above ground at both substations, the Kerite crew installed six new Raychem terminations, three in each location.|
Above ground at both the Sumner and Central Allentown substations, the Kerite crew installed six new Raychem terminations, three in each location.
The Allentown power restoration project took six weeks, one month less than the utility had originally anticipated.
“Circuit failure in a city can affect thousands of people and cost hundreds of thousands of dollars,” said Ian Stangle, Kerite project engineer. “We designed a logistically safe solution for the city of Allentown and executed it in less than two months. Our crews worked tirelessly and efficiently, making sure this complex installation went smoothly and will operate reliably for many years to come.”
More than a year later, the new cable is fully operational and in perfect operating condition. The circuit has experienced no failures.