| What happened? The power grid must not only have sufficient generation capacity to match load, it needs some extra - called spinning or operating reserve. This ensures security - the characteristic where the grid is resilient to any single failure. Because load is not normally controlled (i.e. people can turn loads on and off without permission from the system operator), the system needs to be able to respond to that as well as contingencies like a line or generator trip. Imagine, for instance, that you're fully maxed out on generation with no reserve, and one generator trips offline. You will now need to trigger emergency load shedding very, very rapidly (within seconds) to arrest frequency decline and a cascading, wide-area outage. So you carry a margin of operating or spinning reserve, essentially generation that is available to very quickly ramp its output up or down in response to system conditions. When that margin starts to get eaten away by lack of capacity, you can do controlled load shedding, where you remove loads that have been already marked as low-priority to get some of your margin back. By doing this, you can avoid uncontrolled load shedding, which would have worse consequences. Official notice from CAISO: ----------------------------------------------------------------
NOTICE: 202002424 POSTED: 2020-08-14 18:38:00
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CAISO Grid STAGE 3 System Emergency Notice [202002424] The California ISO hereby issues a CAISO Grid Stage 3 System Emergency Notice
effective 08/14/2020 at 18:36 through 08/14/2020 at 23:59. Reason:
California ISO is Reserve Deficient. Refer to the ISO System Emergency Fact Sheet (http://www.caiso.com/Documents/SystemAlertsWarningsandEmerge...)
for additional detail. The ISO requires load curtailments, use of Interruptible Loads* and
requests Out-of-Market (OOM) and Emergency Energy from all available sources.
Maximum conservation efforts are requested. Spinning Reserves have depleted or are forecast to deplete to levels below
minimum requirements. Load curtailments are required and will continue until
such time as sufficient Spinning Reserves are available. Monitor system conditions on Today's Outlook (http://www.caiso.com/TodaysOutlook/Pages/default.aspx)
and check with local electric utilities for additional information. http://www.caiso.com/informed/Pages/Notifications/AWENoticeL... |