Mishaps bare power grid's vulnerability

By ED TAYLOR
East Valley Tribune
7/25/04

Mishaps that have strained the Valley's power grid, threatened rolling blackouts and forced many to scale back power usage have exposed potential vulnerabilities in a system that millions of people depend on every day, according to some industry observers.

Others, however, say the fact that blackouts have been avoided demonstrates the system is prepared to handle an unusual event.

Utility executives hope some insights will emerge during an investigation into the causes of three major incidents: The June 14 shutdown of all three units at the Palo Verde nuclear plant west of Phoenix, triggered by bird droppings falling on a line insulator miles away; the July 4 transformer fires at the Westwing substation in the northwest Valley; and last week's fire at the smaller Deer Valley substation.

Arizona Public Service, one of the Valley's major electricity providers, suffered another setback Saturday when the huge replacement transformer that is headed to the Westwing substation fell off a trailer in California.

The independent investigators are expected to complete their report in about six months.

The task will be difficult. Any system, including the electric grid, could have more redundancies and safeguards engineered into it, but the prices that power users might have to pay could be more uncomfortable than the occasional inconveniences caused by a less-robust system.

"We have to make tradeoffs every day on reliability versus cost," APS president Jack Davis said Friday during a hearing before the Arizona Corporation Commission, which regulates utilities in the state and is participating in the investigation.
Some observers, including commission member Mike Gleason, argue the ability of the Valley's electric system to survive so many hits this summer without major outages is an indication that it's already pretty robust.

Kris Mayes, another member of the commission, believes the events show the grid is "at risk and vulnerable."

Davis said the investigation team, which will include commission staff, will look at such possibilities as putting concrete firewalls between transformers at substations so a fire in one transformer will not so easily spread to others, creating more distance between transformers to accomplish the same task and repositioning backup transformers so they are more readily available in case of fires. Also considered will be the cost, he said.

What is clear is that the design for transformer substations has changed in the 30 years since the Westwing substation opened at Loop 303 and Happy Valley Road. There are major design differences, for example, between
Westwing and the Rudd substation, which opened last year in the southwest Valley.

Rudd, which is operated by Salt River Project, is built with greater distances between the transformers. Also, it uses three-phase transformers, which have three times the capacity of the single-phase transformers used at Westwing. That reduces the number of pieces of equipment needed, allowing greater separation over the same area.

APS and SRP are the two major electricity providers in the Valley. They divide the region into separate service territories, but share the costs and benefits from major generators, transformers and transmission lines.

The Rudd transformers are surrounded by retention basins filled with rocks. If a fire breaks out in the mineral oil that is used in the transformers as an insulator, the oil will drain into the rocks, helping to smother the fire. Westwing has no such basins, and the July 4 fire in one of the transformers spread to four others, including a backup transformer that was supposed to be available in an emergency.

There are no firewalls at either Rudd or Westwing, but there are firewalls at the Kyrene substation operated by SRP in Tempe.

Firewalls have the drawback of blocking natural air circulation that can help cool the transformers, Davis said. But, he added, "everything will be considered."

Another emerging major issue is whether utilities are paying enough attention to maintenance of equipment that was state of the art when installed but is now 30 years or more in age. Arizona Corporation Commission member Bill Mundell in particular is seeking more information on past maintenance schedules and whether they are sufficient.

"The older the transformer, the more maintenance that's required," he said.

Davis said the equipment is designed to last 40 years and with proper maintenance can last much longer. As a result of the Westwing and Deer Valley fires, APS has already increased thermal evaluations and mineral oil sampling at its substations, he said. But he added, "I don't suspect that maintenance is an issue."

He said APS alone has spent $3.5 billion on infrastructure improvements in the past five years and will spend another $2 billion in the next five years, not including the cost of building additional generating capacity. He said it's not yet clear how much more of its own generating capacity APS will need and how much electricity can be purchased on the wholesale market.

SRP also is doing some investigating. Operations manager Gary Harper said his staff is looking into doing more to discourage birds from flying around power lines - that is in response to accounts that a bird left "organic material" on an SRP power line insulator west of Phoenix before a short circuit shut down the Palo Verde units on June 14.

Harper points to this summer's experience as demonstrating the need for more locally produced electricity that doesn't require longdistance transmission lines. He cited the expansion of the Kyrene plant in south Tempe and the ongoing expansion of the San Tan plant in Gilbert as providing useful backups for transformer outages.