CAISO declared insufficient operating reserve (the generation capacity that is available to quickly ramp up or down to match load and generation), which forced them to drop load to get back within safe operating margins. It's better to do this than let the system get into an insecure state where a forced outage may cause cascading failures.
---------------------------------------------------------------- NOTICE: 202002424 POSTED: 2020-08-14 18:38:00 ---------------------------------------------------------------- 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.
