Huge blackout darkens Yuma, Southwest
September 08, 2011 10:18 PM
BY CHRIS McDANIEL - SUN STAFF WRITER
(c) Yuma Sun
LINK(excerpt)
Maintenance conducted by APS on the Gila Substation northeast of Yuma Thursday afternoon caused a cascade effect that led to the loss of power for up to 5 million residents in Arizona, Southern California and Mexico officials stated.
Among APS customers, approximately 56,000 lost service throughout Yuma, Somerton, San Luis and Gadsden. APS was able to restore power to area customers by 10 p.m.
According to APS, at approximately 3:30 p.m., the North Gila - Hassayampa 500 kV transmission line near Yuma tripped offline resulting in a major power outage.
The line connects to the Hassayampa Switchyard, which interconnects the generating facilities in the vicinity of the Palo Verde Nuclear Generating Station located approximately 60 miles west of Phoenix, and serves as a major electrical conduit into Southern California.
“From that switchyard, the power goes west out of there on the North Gila - Hassayampa 500 kV line, and that is the only line that goes from Arizona to San Diego County, and it goes through Yuma,†explained Jeff Lane, spokesman for the Salt River Project, which operates the Hassayampa Switchyard.
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Basically, and I'm only guessing at this point since I haven't seen any reports yet and APSC, SRP, and SDGE are still working on the issue, this is what I'm thinking happened:
Workers doing maintenance on carrier equipment for the 500KV line at the ends of the line. For whatever reason, not all the trips are removed or considered, and when the line is tested (normally all trips are blocked and line won't trip) it inadvertently trips.
Huge amount of power (500KV line could easily handle 1500-2000 MW) now not being transmitted on this line. VERY hot day (110-plus in parts of CA/AZ.) EVERY line now plowing in trying to make up for this lost transmission line, cascading to the point where all the lines into the demand (in this case, SD), just say, "Screw it--TRIP!" Which is also what happened with San Onofre--the lines out of there (which are only 230KV) also dumped, which will trip the turbines and scram the plants.
This is why ISOs get so touchy when you want to do ANYTHING with ANY bulk power line. This is, in essence, a scaled-down version (but still huge) of the 2003 Northeast blackout.
