Critical Causeway Gets Upgraded With Automated Power System

Industrial power systems operators are becoming increasingly sophisticated in their requirements for system protection. Engineers of industrial power installations are adopting the standards and practices similar to those of utilities, incorporating the technologies needed to gain added economies, reliability, and safety through automation, enhanced communications, and system integration. The trend is toward more comprehensive power management – resulting not only in improved system protection, but also the ability to automatically and quickly reconfigure and restore electric power when outages occur.

The Lake Pontchartrain Causeway in Louisiana features an automated distributed power system.

While not a typical industrial application, the recent modernizing of the Lake Pontchartrain Causeway, the world's longest overwater bridge, is a good example of implemented power system delivery and protection. Spanning Louisiana's largest inland body of water, the 24-mile causeway provides vital link between New Orleans and communities to the north. It also serves as a primary hurricane evacuation route for coastal areas.

In 1995, The Greater New Orleans Expressway Commission (GNOEC), which operates the causeway, initiated a $79 million plan to modernize the bridge's infrastructure. A major component of the project was the complete replacement of the high-voltage electrical system, which was inadequate in terms of power and nearing the end of its useful life. A new electrical system was needed to power drawbridge operation, cell phone towers, toll facilities, and a series of variable-message warning signs to be installed along the often fog-enshrouded causeway.

For electrical consulting and project management, GNOEC hired Gulf Engineers and Consultants (GEC), which proposed an automated distribution system capable of automatic fault detection, isolation, and restoration, communicating over fiber-optic cable.

Designing Distribution

The design of the distributed system consisted of 11 resettable fault-interrupting switches rated 27 kV, 600 ampere continuous in a loop system. The switches were placed at two-mile intervals along the bridge. A three-way switch, located at mid-span, would serve as the normally open tie point. Power sufficient enough to support the entire grid would continue to be provided from different utilities on each side of the bridge, in the event of an outage from either utility.

In the event of a fault between a sectionalizing switch and a load, GEC's specifications called for a resettable fault interrupter in the switch to automatically isolate the faulted cable section. If a fault occurred between two sectionalizing switches on the main cable, one of the shore-based switches would isolate the bridge from the main power source, and then reconfigure the system and restore power to the isolated segment by feeding from the alternate source. The system also automatically senses the restoration of power and returns the system to its normal status.

A Canada Power Products switchgear is placed at both ends of the causeway for fault isolation and sectionalization between utilities on the causeway.

Eventually, Canada Power Products Corp. was chosen to provide a fully integrated system solution including switchgear, switchgear controllers, protective relays, SCADA, automated restoration software, relay settings, and integration services. The switchgear packages were installed in prefabricated control houses and "dropped" into concrete pedestals mounted atop pilings driven into the lakebed. Cable was run in trays suspended between the northbound and southbound bridges and routed to and from the control houses.

Switchgear Setup

Each switchgear package used on the bridge is equipped with a fiber-optic modem/transceiver, an RFI control box, internal 14,400:120 V potential transformers, and an SEL-351S protection and breaker control relay from Schweitzer Engineering Laboratories (SEL).

"We opted to go with SEL-351S relays primarily because of their flexibility and programmability," says Mani Nassereddine, engineering manager at Canada Power Products. "The requirements of the project were such that we needed to program the relays with a database to fit the application. We needed the database spread across the whole bridge, locally, instead of being centralized to one location." Nassereddine says that SEL's Mirrored Bits technology was critical to the system's automation and transfer-trip scheme.

Mirrored Bits is a patented communications technology for providing high-speed, point-to-point communications of relay contact-status bits as well as high-speed bus protection sectionalizing, restoration, and interlock schemes.

Nassereddine says the project also benefited from another SEL product. "We also needed communication between the relays across the entire bridge," he says. "The SEL fiber-optic transceivers made that very simple, and fit together so that we didn't have to worry about integration. It was simply a plug-and-play setup."

Integration with Canada Power Products selection of controls was another benefit of the SEL-351S. "We use controls from Survalent Technology for the automation of our products. It was relatively easy to integrate the SEL-351S because it was working as an RTU for us as well as a protection relay, which was also very attractive," Nassereddine adds.

The end result was a fully integrated and automated power system for a bridge that needs to stay operational in order for boats to pass through and for people of the area to get back and forth from work or to evacuate should an emergency arise.