Arizona Public Service officials said Monday they are making progress in implementing recommendations from two consultants on how to avoid power disruptions such as afflicted the Valley’s electric system last summer.
At a hearing in front of the Arizona Corporation Commission, APS president Jack Davis said the utility is upgrading technology, replacing key components, building concrete fire walls at substations and enlarging maintenance staff to reduce the chances of the same types of failures happening again.
Last summer, the Valley’s electric grid was afflicted by three major incidents:
• A June 14 power surge, apparently started by a bird on a 230-kilovolt transmission line in the West Valley that caused the temporary shutdown of all three reactors at the Palo Verde nuclear plant west of Phoenix.
• A July 4 fire at the Westwing substation in the northwest Valley, which cut the Valley’s power supply for weeks and forced customers to conserve during the hottest months of the year.
• A July 20 fire at the Deer Valley distribution substation in the northwest Valley, which caused local power outages in Phoenix.
Studies by the consultants found that the June 14 grid disturbance and the July 4 fire were related, but the July 20 fire was a separate incident caused by the failure of a bushing at the Deer Valley station.
The June 14 line fault caused damage to the Westwing substation that was not detected in later inspections, and a July 4 explosion and fire in one of the transformers spread to six other transformers, drastically reducing the amount of power.
Several unusual factors contributed to the July 4 fire, the study said, including the failure on June 14 of a usually reliable relay, which has an average failure rate of just once every 2,000 years, and miscommunication between an operator at the APS operations center in downtown Phoenix and a field technician at Westwing, which caused an overloading of several transformers at Westwing.
The consultants, EPRI Solutions and Harold Moore and Associates, recommended that additional redundant relays be installed to protect the system in the event of line faults, improvement in communications protocols, improved diagnostic tools to detect equipment damage and other improved maintenance practices.
APS officials said they have either adopted those recommendation or will adopt them. "I have been in this business for 32 years, and this is a oncein-a-career event," Davis said.
The relays at the Westwing station and 230 kilovolt Westwing line have been replaced, and APS is looking at updating protection systems at other stations and lines, said Cary Deise, APS director of transmission operations and planning.
Added backup relays are being added at Westwing and two other substations, he said, and new communications procedures between operators and field personnel have been implemented.
Also the utility has been working on a plan to phase out and replace bushings of the type that caused the Deer Valley fire, said Jan Bennett, APS vice president of customer service.