What happens when frequency increases to high levels in relation to ACE limits?

When frequency increases to high levels, the appropriate response regarding the Area Control Error (ACE) limits is that no low ACE limit is applied. This situation typically occurs as a response to an increase in power generation or a decrease in load, which can cause the system frequency to rise.

In the context of transmission operations, ACE is a crucial metric used to assess the balance between generation and load within a control area. When frequency increases significantly, operators may focus on managing the high frequency situation without the constraints of a low ACE limit. The rationale behind not applying a low ACE limit in this case is that the priority shifts to maintaining the stability and safety of the grid at higher frequencies, where the risk of system instability or equipment damage could increase if corrective actions are not taken promptly.

The other concepts related to ACE limits, whether that involves high limits or operational limits being ignored, do not accurately capture the essential operational response tied to managing high frequency situations effectively. Therefore, recognizing the absence of a low ACE limit during high frequency events reflects a proactive approach to grid management.