Shut-Off of Backups Blamed for Extended L.A. Power Blackout

Restoring power to much of downtown Los Angeles after Tuesday’s blackout took so long--more than nine hours--because utility workers decided to shut off backup transformers as a precaution after an early morning blaze destroyed a primary transformer, city officials said Wednesday.

Department of Water and Power officials acknowledged Wednesday that they have no tertiary system to provide electricity to much of the downtown area.

They said that such a prolonged blackout could occur again if the single Skid Row power receiving station that serves much of downtown is knocked out of service.

That station consists of three transformers that receive electricity at 230,000 volts from far-away power plants and reduce it to 34,500 volts for distribution around the city.

Blacked Out at 2 A.M.

The fire in one of the 20-foot transformers blacked out the financial district and 30 of the city’s tallest buildings about 2 a.m.

Tens of thousands of workers were idled, in some cases until nearly noon.

The cause of the fire has still not been determined, said Lawrence Green, manager of DWP’s system maintenance department.

But Green speculated that recent earthquakes may have loosened something inside the transformer that led to a short-circuit. The short-circuit in turn may have generated gas that mixed with oil inside the transformer and led to the fire.

Green said that short-circuits in such large transformers are rare--and short lived. They typically last only a few tenths of a second, he said, before protective devices isolate them automatically. Short-circuits leading to fires, he said, are “extremely rare.”

Put Out in 90 Minutes

Tuesday’s fire at the receiving station that serves about one-third of the downtown area was put out in an hour and a half.

The burning transformer immediately shut itself off as it was supposed to, Green said.

Officials decided to shut off the two other transformers.

They feared that oily soot from the fire would contaminate the transformer’s insulation, Green said.

“After the fire was gotten out . . . theoretically those transformers were now healthy and ready to go back (into service), but . . . they were still dirtied up by the oily soot,” he explained.

While thousands of office workers stood around on sidewalks, waiting to get into work, blocks away, 15 DWP employees crawled atop one of the transformers.

“The only way to get that (oily soot) off is just to hand-wipe it,” Green said. Then it was “re-energized.”

Any two of the transformers can, in a pinch, do the normal work of three, Green said.

Shortly before noon, both were back in service and life in downtown returned to normal.

Green said DWP was able to restore power to outlying sections of the downtown area served by the Skid Row receiving station by switching them to adjacent stations.

But DWP’s switching capability is not designed to use adjacent stations to pick up the entire load of a disabled station, Green said.

“What was possible to pick up on adjacent stations was done,” he said, and power was restored for some of the 37,000 customers in the blackout.

‘Basically Stuck’

“Then we were basically stuck until we could get one transformer (at the stricken station) hand-wiped and back in service to pick up the remaining load.”

“What you saw is about the extent of our capability to do outside switching in,” he added. “If this same thing happened again, you’d have about the same sort of outage.”

Green explained that the Los Angeles power transmission system is “radial” rather than “interconnected,” so that if one service area is blacked out, another cannot necessarily feed it with power.

In some cities--New York, for example--service areas are interconnected, so that a power failure in one can be more readily cured.

But there is a disadvantage to New York’s approach.

Huge blackouts there caused by the failure of the long-distance power supply have lasted longer than they would here, Green said.

New York City’s power system is so interconnected that it has to be restarted as one huge entity.

Los Angeles’ could be restarted in sections, he said.

Times staff writer Nieson Himmel contributed to this article.