June 20, 2008
Lightning took out plant for 3 months
Rothschild, WI – After a thorough review of the events surrounding the October 2007 lightning strike that damaged the Weston 3 power plant, a committee comprised of Wisconsin Public Service employees and members of two expert consulting groups has issued its findings.
The report indicates that one of the root causes of the damage was an intense lightning strike to an on-site transmission tower, not owned by Public Service, which was properly grounded but not bonded to the Weston plant grounding system. The resulting power surge through the ground impacted several pieces of equipment as well as the plant’s computerized control system, and led to millions of dollars in damage to the plant.
The investigation committee found that the Public Service lightning protection system met applicable industry standards. Transmission poles are not commonly grounded to generation plant’s systems. However, the company’s lightning protection consultant found unusually high soil resistivity at Weston and recommended that the towers be bonded to the Weston Plant’s grounding system, which has been completed.
“If the transmission tower had been connected to the plant grounding system, we’re fairly certain we could have avoided much of the damage to plant equipment,” said Terry Jensky, Vice President of Energy Supply Operations.
The power surge from the lightning strike caused the critical loss of four of five power supplies to the plant’s control system. The remaining backup source of power was unavailable because of a mis-configured breaker. The loss of control system power to a lubrication system led to turbine/generator damage when the unit slowed to a stop without sufficient bearing lubricating oil.
An inspection following the lightning strike found that all of the other 17 breakers of this type were properly configured. “The damage to the Weston 3 plant resulted from the extremely unlikely coincidence of very low probability events,” Jensky said.
Jensky also complimented the Weston 3 plant staff on their reaction to the lightning strike and the repair effort that followed. “This all occurred in a timeframe ranging from a handful of seconds to a few minutes. It was pretty traumatic for the employees involved. They reacted very quickly to the event but because multiple fires had started, there was a considerable amount of smoke inside the plant. The first priority for plant staff was to take actions to safely deal with the fire. Only after the fires were under control could the employees begin to simultaneously deal with the smoke and manually start processes that lost power.
”Our employees reacted well under the circumstances, and worked hard to return the unit to service in only 95 days. Given the amount of damage to the plant, that is remarkable.”
