Client: Greater New Orleans Expressway Commission - Lake Pontchartrain Causeway
Completion Date: 12/8/2006
Scope of Services
Preliminary Plans and Specifications
Final Plans, Specifications, and Estimate of Probable Construction Cost
Bidding Services
Construction Administration Services
Project Summary
GEC was the lead firm in the design and construction engineering for a new electrical power distribution system for the Lake Pontchartrain Causeway. With the old system installed in the late 1950's and the addition of electrical loading over time, a new system was in order from an age and capacity standpoint. After extensive study and research, a new system voltage level of 24,900 was chosen. In addition, due to the Causeway being a hurricane evacuation route and the level of traffic occupancy, a high level of reliability was required in order to maintain power service to the critical motorist information system and other significant systems.
Design of the new system was to incorporate existing and future electrical loading, was to have a high state of reliability, and was required to have remote control and monitoring of the field apparatus. The system was designed in a radial configuration from the north to the south shore of Lake Pontchartrain and powers the entire 24 miles of the Causeway Bridge, including the North and South Plazas. 25kV switchgear is installed at strategic points along the length of the bridge with various sized step down transformers of 25kV - 480Y/277 volts and 480V - 208Y/120 volts.
Installed at the system ends and along the main line feeder is SF6 electrical switchgear with associated solid state electrical relays (see figure 1). System normal configuration is with Entergy powering the southern 12 miles and CLECO powering the northern 12 miles. In the event of loss of source, the system goes into the emergency configuration with the system automatically opening the de-energized shore switch and then closing the tie-switch located at center-bridge, thus allowing the entire system to be fed by one utility. Upon the restoration of the utility, the system returns to the normal configuration either manually or automatically which is user selectable.
In addition to the automatic transfer scheme, the system also includes an automatic reconfiguration feature that extinguishes all primary line faults through the use of main-line solid state electrical relays (see figure 2). In the event of a primary line fault, the protective devices located on the shore operate, thus powering down and protecting an entire 12 mile section of the system. The protection software then begins its fault checking procedure and automatically reconfigures and sectionalizes the system based upon the location of the fault. The faulted section is then isolated and power restored to the switchgear located on either side of the fault. Once the fault is repaired, the system is manually returned to the normal configuration.
At the heart of the protection schemes is the master station and supervisory control and data acquisition system. The main function of the SCADA system is to obtain various local and remote data and perform certain functions based upon the analysis of that data. In addition, the system is also capable of remote operation and control of the electrical apparatus.
Communication among the solid state electrical relays and the master station is performed through the use of an optical fiber communications system. A single cable consisting of 144 strands of single mode fiber run the entire 24 miles of the bridge structure; from the South Toll Plaza to the North Toll Plaza and from the North Toll Plaza to the GNOEC North Shore Maintenance Facility.
In addition, new emergency generator systems with automatic transfer for the South Toll Plaza and North Shore Maintenance Facility were designed and installed (see figure 3). The systems were designed to accommodate current and future electrical system loading, to provide for an operational system for extended time periods, and to perform in adverse and inclement weather conditions.
System features for the South Plaza site are a 200kW standby generator with extended capacity alternator for non-linear loading and rated at 208Y/120 Volts, 3 phase, 60 hertz, automatic transfer switch, manual transfer switch with standby receptacle, remote annunciator panels for system monitoring, 1,000 gallon, double wall, sub-base diesel fuel tank with ventilation and gauges, and remote fuel fill station.
System features for the North Shore Maintenance Facility site are 200kW standby generator (see figure 4) with extended capacity alternator for non-linear loading and rated at 480Y/277 volts, 3 phase, 60 hertz, automatic transfer switch, remote annunciator panels for system monitoring, 2,000 gallon, vaulted double wall, diesel fuel tank with ventilation and gauges, 2,000 gallon, vaulted double wall, gasoline fuel tank with ventilation and gauges, diesel and gasoline pumps for automobile fueling, fuel tracking system, physical fuel spill containment, and remote fuel fill station - double arrangement.
For both installations, system operation is with the generator system automatically starting and assuming the load upon loss of main power. Upon the restoration of main power, the generator system will automatically return to the primary source after a user definable time duration. In the event of a generator system malfunction, the system can be reconfigured for use with a GNOEC portable generator system through the use of the manual transfer switch and standby receptacle.
Generator system was designed according to industry standard principles and practices and in conformity with applicable codes and regulations. Equipment was required to be listed by UL or other recognized testing laboratories wherever possible and was required to meet ANSI and/or NEMA standards. Recommended practices as published by ANSI/IEEE were followed to the extent possible. Specifically, IEEE Standard 446 - Recommended Practice for Emergency and Standby Power Systems for Industrial and Commercial Applications.
figure 1 |
figure 2 |
figure 3 |
figure 4 |
