Replies

The Pacific DC Intertie, (PDCI) a 500-thousand volt transmission line that runs between Southern Oregon and Southern California suddenly and unexpectedly dropped out of service just before 4:00 P.M. today. The loss of more than 2,800 megawatts of power coming into Southern California, coupled with the area’s high demand required a reduction in system load to keep the grid in balance. Loads in southern California were running about 2,000 megawatts higher than anticipated due to temperatures that were up to 14 degrees higher than forecast.
No details are available yet about what caused the PDCI to trip off line.

The Pacific DC Intertie, (PDCI) a 500-thousand volt transmission line that runs

Deja vu ... shades of 1996 ...

www.spectrum.ieee.org/WEBONLY/publicfeature/jun99/grid.html

Improving Grid Behavior
The inglorious summer-of-1996 blackouts taught the West to improve emergency control and protection and to sharpen simulation techniques
The 1996 outages
All this restructuring was just getting under way in the western grid system of the United States when in July and August 1996 two large-scale power outages occurred. They were the culmination of a series of four increasingly severe failures.
The reasons for the 1996 failures were many, and in some respects they may represent "a bad statistic." That year, conditions for the generation of hydro power in the Pacific Northwest were better than they had been in any year since 1976, so that power transfers to California were much greater than usual.
Still, the failures served as a wake-up call that high reliability must be maintained in the more competitive environment that was emerging. In what follows, a brief description of the summer-of-1996 failures precedes an outline of the most important lessons learned and the actions taken to reduce the risk of similar events.
...
The 2 July failure
On Tuesday, 2 July, temperatures were around 38 °C in southern Idaho and Utah, and loads were very high. Also, power exports from the Pacific Northwest to California on the Pacific AC and DC interties were high (4300 MW and 2800 MW, respectively). The Pacific AC Intertie rating at the California-Oregon border is 4800 MW, and the Pacific HVDC Intertie rating is 3100 MW.
The trigger event occurred at 14:24 hours with a flashover to a tree on the Jim Brid-ger-Goshen 345-kV line. Faulty operation of a ground unit of an analog electronic relay tripped the parallel Jim Bridger-Kinport 345-kV line. The two long, series-compensated lines integrate the four-unit, 2000-MW Jim Bridger power plant in Wyoming through a transmission network with Pacific North-west load centers some 1300 km away.