When Storms Kill the Power Grid, Generators Can Keep the Hurricane Center Alive
When a hurricane threatens anywhere in the Western Hemisphere, the National Hurricane Center in Miami becomes a maelstrom of meteorological activity.
NHC forecasters gather and compile data from the storm and its surroundings to pinpoint its location and strength and to track its movement. They use huge computers to massage the data in mathematical models, and they analyze the results to predict where the storm is going. Then they issue watches and warnings to alert people in its path.
When Miami falls within that path, the forecasters also alert their support staff well in advance of a storm’s arrival to turn on the generators that will keep the NHC in operation if local utility service fails—which happened twice in 2005 as Hurricanes Katrina and Wilma ravaged Florida Power & Light Co.’s grid.
Three 300-kW Cummins Onan diesel gensets, sheltered from the elements inside a windowless bunker of reinforced concrete, provide standby power for the building that houses the NHC. “We have a backup for a backup,” says John L. Moss, facility engineering technician. “The generators all start at the same time. Whichever one synchronizes first takes up the load, and the second synchronizes to it and runs in parallel with it. The third drops off and waits in the background.
“If one of the others drops off for whatever reason, such as a broken hose or a high engine temperature, the generator waiting on standby will come online.”
The building’s load averages about 290 amperes. “One generator would run this whole building,” Moss says. “That would put a strain on the generator, but it’s possible.” In a pinch, some lighting and other non-essentials could be shut down to ensure that enough power is available for all critical equipment and systems.
The electrical system includes transfer switches that activate the generators automatically if a random utility power outage occurs. To test the system, the transfer switches are programmed to turn on and run the generators each Tuesday morning. “Cummins recommended that we let the generators heat up and run with a full load for a minimum of one hour a week to make sure everything is OK,” says Phillip A. Judd, electronic systems analyst. “This is very helpful. Sometimes we spring a leak in a coolant hose. We’ll find it during a test.”
Bridging the gap between utility and generator power, three Mitsubishi 2033A Series uninterruptible power supply units deliver current from a total of 90 batteries.
“The UPS units run critical items such as computers, meterological equipment, and the radar display,” says Salim Leyva, supervisory information technology specialist. “If we lose utility power, the UPS units come on until the generators come up to speed. The initial installation had smaller UPSs, but we changed them several years ago.
“Once we go to generators, the whole load transfers. If there is any lag or sag in power, the transfer switches automatically switch over. As a storm approaches, we will manually perform the transfer in a preventive mode.
“We have an agreement with FP&L as part of their load-management program. If the grid becomes unstable, they can remotely shunt us off onto the generators—or we can do it ourselves beforehand. It’s a pre-emptive thing.”
As a hurricane approaches, grid power tends to flicker and fade before it finally fails. “The UPSs can’t keep up with repeated surges and sags,” Moss says, “so they will shut down to protect themselves, leaving critical electronic equipment vulnerable to harm. Normally we don’t let matters get that far. If we know a storm is coming, we’ll switch over to the generators a day before it’s supposed to hit.”
Moss says the switchgear in the generator room, installed more than a decade ago, is obsolete and targeted for replacement. “It works fine,” he says, “but it’s big and bulky. Smaller and better switchgear is available now. If we have problems with the breakers, they’re pretty expensive to replace—about $14,000—so we’re better off updating the system. We’re researching that now.”
Quite a Crowd
Although the NHC is the public face of the federal government’s hurricane forecasting effort, it resides within a larger agency, the Tropical Prediction Center (TPC), which in turn is an arm of the National Oceanic and Atmospheric Administration in the US Department of Commerce. The TPC monitors weather conditions across almost half the globe, from the eastern North Pacific Ocean through the Gulf of Mexico, Caribbean Sea, and North Atlantic Ocean to the west coast of Africa.
In addition to the NHC and TPC, the building—officially called the Tropical Prediction Center—also houses a local National Weather Service forecast office serving 6.5 million people in seven southern Florida counties.
During a hurricane, as many as 125 people could be in the 25,200-square-foot building. About 70 would be meteorologists and support personnel with information-technology and electronics expertise, working in shifts around the clock. “This becomes a shelter,” Judd says. “Members of our staff can bring their families in, although not many do so. We average 10 to 15 family members per storm. We also have media representatives in the building, sometimes as many as 40. They don’t bring their families, but the TV people run their lights and cameras.”
Churches and restaurants sometimes deliver food to these hurricane-watchers, but such generosity can’t be relied upon because high winds and flooding may isolate the building for several days. Every occupant preparing to ride out a storm there is told to bring enough nonperishable food for three days of sustenance, which some interpret as an ample supply of the ingredients for peanut-butter-and-jelly sandwiches.
To keep everyone comfortable and productive, and to maintain the operational integrity of the computers and electronics, the generators provide enough capacity to air-condition the entire building. The main climate-control system employs variable-air-volume boxes to create 63 discrete zones, allowing the temperature in one area to be changed without affecting the rest of the building. Two 60-ton Trane condenser units serve the operations area and a 40-ton Trane condenser unit supplies the administrative offices. Each condenser unit has four compressors and an individual air handler.
“The two 60-ton units don‘t run at same time,” Moss says. “We rotate them every 72 hours, so we don’t put all the hours on one unit.”
A separate air-conditioning system supplies chilled air to a plenum floor in the main computer room, providing precise, reliable control of room temperature, humidity, and air flow to dissipate heat generated by the powerful computers in the room. This specialized system consists of three Liebert System 3 units from Liebert Corp. of Columbus, OH, each with a 15-ton condenser.
Thanks to Andrew
When Hurricane Andrew blew through southern Florida in 1992, the NHC was located in a 12-story office building across from the University of Miami in Coral Gables. “We were going to move anyway, but Andrew speeded it up,” says Judd. “The radar was on top of the building. Andrew blew it right off.”
The current building opened in 1995. It occupies slightly more than three acres on the main campus of Florida International University, which leased the site to the federal government for $1 a year. Located 16 miles west of downtown Miami, the low, fortress-like structure has 10-inch-thick walls of concrete reinforced with steel rebar.
The building occupies a site on the edge of the Everglades. At this location, flooding due to torrential rains during a hurricane or tropical storm is a concern but not a problem. Although the surrounding terrain is just 7 feet above mean sea level, the building sits atop a raised mound at an elevation of 12 feet, enough to keep it high and dry even when floodwaters surround it. “During Hurricane Irene in 1999 and an unnamed storm in October of 2000, our building was an island,” recalls Russell L. “Rusty” Pfost, the local forecast office meteorologist-in-charge.
The site is far enough from the ocean that a hurricane storm surge wouldn’t reach it. A nearby canal could overflow if enough rain were to fall during a storm, but that hasn’t happened and is anticipated to occur only once in more than 100 years.
“We’ve never had water in the building—not even close,” Judd says. “After Irene, the water was pretty much gone after one day. We planted Fakahatchee grass that acts like a marsh to help keep the water at bay, and the limestone rock underneath us is a benefit in helping the water level decrease rapidly. The limestone is porous and sucks the water right down.”
“We have steel shutters on every window, and large panels on the doors,” says Pfost. “Putting them up is a huge undertaking because the building is so large. Once we get them up, they usually stay up for the entire season, even though they make the interior really dark.”
Ample Fuel Supply
The generator installation was designed and constructed at the same time as the main building. It occupies a separate structure adjacent to the back door of the main building. The generator building, also constructed of reinforced concrete walls 10 inches thick, is 40 feet long, 27.75 feet wide, and 25 feet high. The main building and the generator building both have a 125-mph wind rating.
Between the generator building and a service drive stands a 10,000-gallon diesel-fuel tank made by Convault Inc., of Denair, CA. The welded stainless-steel tank is surrounded by a quarter-inch of Styrofoam insulation, which in turn is wrapped in an impervious membrane of 30-mil high-density polyethylene to contain any leaks from the tank and to guard the tank against corrosion. Then this package is encased in a 6-inch-thick vault of reinforced concrete, poured all at once so it won’t have joints or heat sinks. The monolithic concrete vault provides two-hour fire protection as well as ballistic and vehicle-impact protection. An exterior coating of water-based epoxy paint protects the tank from extreme weather conditions. The exterior of the vault is 29.5 feet long, 7.75 feet wide, and 7.5 feet tall.
In addition, each generator has a “day tank” that holds 150 gallons. The diesel fuel is treated with additives to prevent sludge formation.
An automated liquid level-control system from Pneumercator Inc., of Farmingdale, NY, manages the process of refilling the individual day tanks. When a day tank reaches the half-empty mark, sensors turn on a pump that draws diesel fuel from the large outdoor tank through .75-inch black pipe enclosed in four-inch PVC pipe. The piping rises from the top of the outdoor tank, crosses above the walkway between the tank and the generator building, and penetrates the side wall of the generator building. The Pneumercator system employs point level controls based on float-actuated level switches, a fuel gauge for the outdoor tank, and a test device that monitors the system for leaks and sounds a loud alarm if a leak is detected.
As a storm approaches, Moss tops off the tanks so enough fuel will be on hand to run the generators for a couple of weeks—far longer than any outage the building has endured in its 10-year history. “We’ve got a high priority with FP&L, second to the hospitals,” Moss says. “Because we’re in the lifesaving business as well, we’re normally not out for too long, and we can usually get fuel within three days.”
Author's Bio: George Leposky is a science and technology writer based in Miami, FL.