UPDATE 1-FPL cites human error as cause of Florida blackout

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HOUSTON, Feb 29 (Reuters) - FPL Group's (FPL.N) Florida utility Florida Power & Light said preliminary results of the investigation into Tuesday's four-hour blackout indicated that human error was the primary cause.

The blackout affected about 584,000 FPL customers in South Florida, the Juno Beach-based company said in a release on Friday.

A total of about 1 million customers of four utilities across the state lost power as emergency safety systems were activated to prevent long-term damage to power plants and transmission equipment.

FPL said preliminary findings indicated that a field engineer diagnosing a problem switch at a west Miami substation disabled two levels of relay protection systems without authorization. Those safety mechanisms are designed to isolate problems to one piece of equipment or one location.

Disabling both systems was contrary to FPL's standard practice, said FPL President Armando Olivera.

He said a voltage drop at the substation could not be contained. The situation triggered other FPL safety systems, forcing the shutdown of 26 transmission lines, 38 substations and 3,400 megawatts of generation, a more extensive outage than described by the North American Electric Reliability Corp (NERC) earlier in the week.

The generation loss automatically launched a "load-shedding" program to cut power consumption by 4,000 megawatts across the state. Most service was restored in less than five hours.

The field engineer was suspended and FPL has taken steps to review standard procedures with its employees to prevent a recurrence, Olivera said.

"While in this instance we failed to perform to our expected standards in regard to reliability, safety was never an issue and the safeguards built into our system worked as intended," Olivera said in a statement.

"To this point, we have no indication that there are any deficiencies with the design of our facilities or with our maintenance procedures," he said.

FPL's two 693-megawatt nuclear reactors at the Turkey Point power plant remained shut Friday for testing and work unrelated to the blackout, FPL said. Officials would not say when the units might return for competitive reasons.

Turkey Point 5, an 1,150-MW gas fired unit, and smaller generating units at FPL's Lauderdale and Martin plants were also shut briefly by the outage, Olivera said.

FPL's blackout was the largest to fall under tough, mandatory reliability standards and penalties put in place after the August 2003 Northeast blackout.

Olivera said it was "too early" to say what financial consequences the utility could face if violations are found.

NERC and the Florida Reliability Coordinating Council (FRCC) are investigating the outage to determine whether all utilities complied with the new standards and if there are lessons that could benefit all utilities. (Reporting by Eileen O'Grady; Editing by David Gregorio)