July 15, 2004
By Rocky Scott, DEMOCRAT STAFF WRITER
PURDOM PROBLEMS
The Purdom plant operated by Tallahassee's electric utility came online in September 2000. But the $110 million facility has had its share of problems, starting with an ill-fated attempt to load a 250-ton generator onto a truck to transport the equipment to the St. Marks site.
• In November 1999, the generator fell from a truck after being transported by train to Tallahassee. After lying on Atlas Road for several days, the generator was shipped to Chicago, where it was inspected and pronounced undamaged by the fall. The generator was returned in November and the plant was scheduled to begin operations in May 2000. But several delays pushed the start date to September.
• In December 2000, city commissioners had to spend $215,000 to process 2 million gallons of water used to wash the inside of the plant's cooling tower. State law barred the discharge of the polluted water until it was treated. City officials offered hepatitis B shots to dozens of workers in March 2001 who might have come in contact with inadequately treated wastewater that was inadvertently pumped into the Purdom plant. Later that month, contractors had to replace several pieces of equipment at the plant because the concentrated saltwater being discharged by the plant's cooling tower was corroding the water-treatment system.
• In March 2002, petroleum contamination was found on the plant's grounds. It was thought to have come from the St. Marks refinery.
• In February, a circuit breaker failed and the resulting damage to the plant was placed at $8 million. Some of the damaged equipment had to be made by hand and it was July 2 before Purdom came back online.
The bad news is a faulty $100 cable triggered a massive shutdown of Tallahassee's electric utility Tuesday. The good news is the system worked exactly the way it was supposed to, a city official said.
"The cable didn't function properly," said Kevin Wailes, general manager of the city's electric utility, on Wednesday. "When that happened, the control system said, 'Uh-oh, I've got to shut the plant down.'"
Wailes said the Tuesday afternoon blackout, which lasted for about three hours and affected about half of the city's 97,000 electric customers, started with the faulty cable at the Purdom power plant in St. Marks.
"It's just a ribbon cable that runs between two cards in the control system of the plant," Wailes said.
Cards are pieces of hardware in a computer system that help store and transmit information. A ribbon cable is a short, flat strip that moves information between cards.
"This particular cable, after it's been in place for a while, will loosen because of vibration. That causes corrosion at the cable's contact points," he said.
Wailes said the faulty cable was repaired and reinstalled Tuesday and that a new cable had been ordered.
Wailes said General Electric officials told him the problem with the cable had first been identified in 1999 and a bulletin had been sent out to utilities using GE Energy generators and computer hardware.
But the Purdom generator, built by GE, was purchased after the technical bulletin was issued, Wailes said, "so we didn't know there had been a problem. It was supposed to have been fixed."
Jan Smith, a spokeswoman for GE Energy, said the company had built about 10,000 generators of the type used at Purdom. She said about 1,000 of them use the software and hardware found at the Tallahassee plant.
She said that cable failures occur "only about three or four times a year" and that the failures rarely lead to a complete generator shutdown.
Wailes said the computer software and hardware that controls and monitors the city's three power plants - Purdom, Hopkins and Corn - is designed not only to keep all the plants operating efficiently, but to protect the equipment if there is a major malfunction.
Wailes said all city power plants were functioning normally Wednesday.
George King, the manager of the Purdom facility, said when the faulty cable halted the flow of information to the software controlling the plant about 1:45 p.m. Tuesday, "it (the computer system) said 'there is a problem in communication and if I can't communicate, shut down.'"
King said the Purdom plant was producing about 225 megawatts of electricity when it went off-line. By comparison, the average home uses about five kilowatts of electricity a day. A megawatt is a thousand kilowatts.
When the Purdom plant went out, Wailes said, the control system automatically shifted the load to the Hopkins plant west of Tallahassee.
But hot weather and a complex operating scheme that included the use of natural gas and fuel oil to heat the steam for the Hopkins turbines set another series of events in motion, all designed to prevent damage to the plant.
"The other generators that are running are trying to pick up the load," Wailes said. The larger Hopkins turbine, already running near capacity, faltered briefly because the increased load affected its fuel/air mixture.
Wailes said workers at the plant righted the mixture, but the same problem occurred again moments later and the 240-megawatt system automatically shut itself down to prevent damage.
That dumped the entire load for the city on the smaller, 80-megawatt generator at Hopkins, Wailes said, which also shut itself down automatically to prevent damage.
Shortly after 2 p.m. Tuesday, employees in the city electric control center made the decision to start shutting down power to the grid.
"It's against everybody's nature to take load off (reduce power to) the system," Wailes said, "but we had to do it to stabilize things."
He said as the power was turned off, efforts were made to keep power flowing to critical facilities such as hospitals.
Wailes said if power had not been reduced, "the entire grid might have collapsed, and that probably would have taken down Talquin Electric and Progress Electric in North Florida."
About 100 megawatts of power were flowing through the grid after the three major plants shut down, Wailes said, from the city's Corn plant, several backup generators at the Hopkins plant and from power purchases outside Tallahassee's electric grid.
Barry Moline, executive director of Florida Municipal Power Association, said massive generator shutdowns were "extremely unusual."
"Most power outages are caused by storms," he said. "Generator failure doesn't happen that often."
Wailes said General Electric consultants helped Purdom workers identify the problem within an hour after it occurred.
He said the decision was made to start bringing the Purdom unit back online after it was clear no damage had been done to the unit.
But restoring power after a massive blackout also is a tricky proposition, Wailes said.
"You basically bring pieces back on at a time," he said. "We were trying to make sure we brought on circuits with lots of traffic lights on them" to ease traffic congestion. About half of the city's 300 traffic lights were affected by the blackout.
All city generators were back on line and operating by 5:15 p.m. Tuesday, Wailes said.
http://www.tallahassee.com/mld/tallahassee/9156503.htm