Although nearly three weeks have passed since the major transmission substation fire northwest of Phoenix, the threat of blackouts hang heavy over the major population center of Arizona and are expected remain at least through August.

The two principal utilities involved are shifting operations and urging customers to reduce their usage. The fundamental “tightness” in the grid will remain until permanent repairs are completed, and that is still weeks away, they said this week.

The latest substation fire, which knocked out power to 50,000 customers for a short time Tuesday morning, was in the distribution system of Pinnacle West Capital’s Arizona Public Service Co. (APS) utility. It followed a regional transmission substation fire at Westwing on July 4, the residual effects of which are putting the general Phoenix area under the specter of blackouts for the rest of the summer.

With the high temperatures and higher-than-normal humidity due to Arizona’s mid-summer rainy season, the transmission capacity is “very tight,” said a spokesperson at Salt River Project, the Phoenix-based quasi-public sector utility that shares the surrounding Phoenix infrastructure and customers with APS.

“We have made changes in the system to squeeze about as much as we can out of the system, and we’re running all the urban generating facilities [within the Phoenix metropolitan area] pretty much 24-7, but how long can that last?”

The first of three transformer replacements destroyed by the Westwing fire should be in available this week and installed in two weeks, the spokesperson said, but the rest of the equipment and repairs will take the better part of a year.

Combined, the peak loads for ASP and SRP this summer are expected to approach 9,600 MW. Scorching heat that sent peak demand soaring increased the potential for having to institute involuntary curtailments, or rolling blackouts, to keep the struggling grid in the greater Phoenix area intact.

Utility sources said there is more than 10,000 MW of capacity but in some of the pockets of the transmission grid that have had to be reconfigured temporarily as the result of the substation fires, loads could exceed capacity for isolated portions of the system.

Earlier this month there were seasonal monsoon rains that wreaked havoc, and the Arizona Corporation Commission (ACC), which regulates the utilities in the state, was without power for hours in its Phoenix building.

On July 4, the fire at Westwing northwest of Phoenix knocked out the area’s largest power generation facilities, including the three units at giant Palo Verde nuclear generating plant, cutting power capacity in the region by 20%, and repairs had only restored about 5% of the lost capacity last week, according to an APS spokesperson.

Meanwhile, a spokesperson for the California Independent System Operator (CAISO), which set an all-time peak load on three consecutive days last week, said the grid operator’s operations were not directly impacted by the latest Arizona electric system fire, but that it indirectly limits CAISO’s options if an emergency arises in California prompting the CAISO to seek more out-of-state supplies. “Part of our safety net is taken away by the situation in Arizona,” he said.

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