Northeast Utilities (NU; Hartford, Connecticut) had to come up with a solution quickly when its 40-year-old in-line and dead-end splices began failing. To solve the problem, NU replaced 345-kV transmission connectors live. In the process, the utility discovered a new use for an existing technology to improve the reliability of the southern New England transmission grid.

During the high-risk project, which was completed five months early and well under budget, NU and a Quanta Services Inc. subsidiary, PAR Electrical Contractors Inc. of Kansas City, Missouri, successfully replaced nearly 1000 in-line and dead-end connectors on eight circuits along 115 miles of line.

While implosive splicing technology has been around for 30 years, NU is the first utility in the United States to install these splices on live lines. This project has paved the way for other U.S. utilities to employ implosive technology rather than the conventional connector technology on live lines.

Connector Failures

NU didn't even consider replacing connectors live until the utility began to experience connector failures on certain 345-kV transmission circuits that run through southern Massachusetts into central Connecticut. The Bluebird 2156 aluminum conductor steel reinforced (ACSR)-type conductor failures were causing not only service disruptions, but structural damage as well. Many towers on the line are of wood H-frame construction with lattice crossarms. When a mechanical splice fails, the tension on the cable and the weight of the conductor can break poles and bend crossarms.

NU's infrared inspection program found that an increasing number of connectors were exceeding normal operating temperatures and required replacement. The temperature of a connector is a reliable indicator of its fatigue and can be used to predict the risk of failure. To investigate this trend, NU sent the failed splices to Georgia Tech National Electric Energy Testing, Research & Applications Center's High Voltage Laboratory in Forest Park, Georgia. The lab found the old connectors' corrosion inhibitor was leaching out, allowing the elements to leak in and cause corrosion. The problem was exacerbated by the increasing current flowing through the transmission lines, which placed a higher demand on the connector.

Prioritizing Replacements

NU took a proactive approach, devising a plan that would replace every connector on the line within three to five years. The utility determined the first priority was to replace connectors along major roadways and near schools, parks and other public facilities; the second priority was secondary roads; and the third priority was unpopulated areas. In addition, NU increased aerial infrared inspections from once a year to once a month, to help identify the connectors at highest risk.

But, not far into the initial connector replacement process, a line experienced a catastrophic failure during a week of heavy rain. The failed connector was located in a hard-to-reach priority-three area, high on a hill. Crews had to use bulldozers and winches to drag the equipment up the muddy slope. The incident further escalated the urgency of the situation.

NU needed to replace about 1000 connectors in a timely manner — and ideally without disrupting service. Planning an outage on a 345-kV line is time consuming and costly, and requesting continuous outage clearance on eight separate circuits was simply not feasible. The utility then made the decision to carry out the work while the lines were energized.

NU contracted with PAR Electrical Contractors Inc. to complete the work. PAR's safety record and experience with live-line barehand work made the company an appropriate choice to perform the “extreme line work” the project required. Quanta had recently completed a project with American Electric Power in West Virginia using implosive splicing and recommended using the same technology for the NU project.

Implosive Splicing

Quanta reported that implosive splicing was not only easier to perform than the more cumbersome hydraulic compression method, but it also produced a better quality connection. As the name suggests, implosive splicing technology harnesses the energy released in an implosion to fuse the connector to the transmission line to form a mechanically tight, electrically efficient connection.

To install an implosive splice, the two ends of the conductor are inserted inside the ends of an aluminum connector tube, which is prewrapped with explosive cord around its outside diameter. A detonator is then attached to the explosive cord. When the cord is detonated, the energy is directed inward, applying about 400 tons/in² of pressure on the connector. In this way, the conductor and the connector are fused together, becoming one bonded section of conductive line.

In this particular case, the job also required some connectors to be longer than a standard connector. In some cases, these connectors measured up to 8 ft in length.

Removing an old connector from the transmission line left a gap in the line. To avoid disrupting the sag conditions of the line, NU had to find a way to fill this gap. IMPLO Technologies Inc. (Markham, Ontario, Canada), an implosive connector manufacturer, developed a special long connector to complete this gap and avoid the need for a short length of conductor wire joined by two adjacent standard connectors. This turned out to be the largest implosive connector IMPLO ever manufactured.