Featured in World Fence News – September Issue 2012
Eighty miles northeast of San Diego, Calif., NRG Solar is developing the 26 megawatt (MW) Borrego Solar Project. Cost-competitive, renewable power generated by the facility will be sold to San Diego Gas & Electric (SDG&E). At full capacity, the project will generate enough power to meet the energy demands of approximately 20,800 homes.
This is the seventh solar contract SDG&E has signed, boosting its renewable portfolio by more than 300 megawatts. (State regulations require California’s utilities to buy 20 percent of their power from renewable sources, such as wind turbines and solar panels. By 2020, that proportion must rise to 30 percent.)
The Borrego Springs electrical substation was not capable of handling the increase in power generation from the solar farm, and required a significant expansion to upgrade its capacity.
Complicating this upgrade was the fact that the substation is located in a 100 year alluvial flood plain that is expected to receive a water flow of up to 12 inches at least once every century. New construction requirements demanded that the perimeter fence itself meet certain water flow criteria.
The threat of a destructive slurry of water, mud, and debris flowing through the substation required that all equipment and electrical components be elevated several feet above grade. (Issues such as cost and a lengthy permitting process prohibited the relocation of the entire substation.)
The design plan called for a ten foot-high perimeter fencing system with automated lower panels to allow water and debris to pass under.
Besides keeping trespassers out, the fence prevents people from getting too close to the facilities, as parts of the substation are so highly electrified that a person can receive a lethal 69,000 volt shock from six feet away.
Alcorn Fence Co., a major fence contractor in business since 1942, was asked to submit a design and build plan for the substation expansion perimeter fence. Alcorn Fence consulted with longtime partner Steve Johnson from Automated Gate Services (AGS) in Corona, Calif. to help with the automation design.
“We’ve worked with AGS on numerous high profile projects that have required gate automation and they’ve always provided an excellent finished product,” said Nick Dobson, Orange, Calif. branch manager for Alcorn.
AGS was contracted to design and install the automation system. Johnson reached out to another business partner, Controlled Products Systems Group (CPSG), a major wholesale distributor of perimeter access control equipment, for help in identifying the necessary components.
Dobson stressed that reliability of the system was of absolute importance.
“We needed a fencing system that would be secure under normal conditions, and then automatically move upon the presence of water flow,” stated Dobson. Together, Dobson, Johnson and CPSG president Brian Huitt considered several very different designs, eventually choosing what they determined to be the most reliable and simplest system.
Testing proved out a reliable and durable design where the bottom 24 inches of each fence panel was hinged horizontally to allow it to swing up and out of the way of the water and debris flow.
The team then went to work to assemble the automation equipment list.
A primary component chosen for the system was a linear actuator gate operator, the Model 1500, manufactured by Apollo Gate Operators, Inc., a national manufacturer headquartered in San Antonio, Tex.
This unit is strong, weatherproof, and has a history of reliability in the field.
“It is also very well sealed for long life in a hostile desert environment, and is virtually impervious to sand, dirt and other debris,” added Huitt. “Another benefit of the Apollo operator is the internal battery backup. The system’s DC power backup, combined with the substation’s own batbattery backup, makes for a very redundant safety system in the event of a power outage.”
The final design consisted of 33 fence panels, 10 feet high by 15 feet wide, with the bottom two feet hinged on top with bearing hinges from Phoenix, Ariz.-based Guardian Gate Hardware, automated with the Apollo 1500 linear actuators.
The next challenge was automating the entire system to respond to rising flood waters without the need for human intervention. A guard control station was constructed by Controlled Products that incorporates a programmable logic controller (PLC).
The PLC interfaces two water sensors, 33 gates, a test button, a keyed reset, and gate status lamps. The PLC also provides gate status outputs that are integrated for off-site status reports and alarm monitoring equipment.
“Programming the PLC is the magic that makes all of this happen,” said Huitt. “With over 90 employees, a vast majority having field and manufacture experience, we have a lot of talent to draw from. Dave Conway, in our Denver location, handled the coding and programming of the PLC.”
The system operates as follows: When water comes in contact with either of two water flow sensors, a signal is sent to the PLC in the guard control center. The PLC then directs an “open” command to each of the Apollo operator’s control systems.
The PLC also communicates with off-site monitors, alerting officials that the gates are open.
An individual can then visually inspect that the flood waters and debris are clear from the gates and close all of them simultaneously with a single keyed reset wired to the PLC.
“I’ve programmed several more complex PLCs, but never one as unique as this application,” commented Conway.
Alcorn Fence and Automated Gate Services completed the substation’s perimeter fencing system after six months of working in the dry, sunbaked desert.
With two water sensors located in the flood plain, at 100 feet and 250 feet out from the substation, the automated system was ready to manage the forces of nature.
And on July 25, 2012 the designed operation was put to the test! Monsoon rains came down at a rate of five inches in one hour. The lowest placed sensor was triggered by approximately 12 inches of flood depth water and all 33 gates reacted instantly.
“The system worked perfectly and performed precisely to San Diego Gas & Electric’s expectations,” Huitt reported.
Here is contact information for the major players in the Borrego Solar Project fence system: