Control Performance Standard 2

CPS2. A standard intended to limit unscheduled flows.

Last Updated: June 20, 2025

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Definition by NERC

Source: p22

Initially, a 10-minute metric called CPS2 was developed to keep average ACE within specific bounds. CPS2 was originally used to help prevent excessive transmission flows due to large values of ACE. The problem with CPS2 was that it was not dependent on ACE’s impact on frequency. Additionally, CPS2 could cause control actions that moved against frequency. If a BA had very bad performance in one direction for five minutes, the BA could correct this by having equally bad performance in the opposite direction for the next five minutes. Finally, ACE could be totally unbounded for 10% of the month and it didn’t matter whether it was 1 or 1000 MW over the limit. CPS2 did not provide the correct signal for maintaining frequency.

Calculation by NERC

Source: p3

\[CPS2 = \left[ 1 - \frac{\text{Violations}_{\text{month}}}{\text{Total Periods}_{\text{month}} - \text{Unavailable Periods}_{\text{month}}} \right] \times 100\]