What percentage should frequency relaying not exceed when considering dynamic reserve?

In the context of maintaining system reliability and stability, frequency relaying is a critical component used to monitor the frequency of the electrical grid and subsequently take protective actions. Dynamic reserves refer to the additional capacity that can be called upon quickly to meet unexpected demand or to compensate for unexpected generation losses.

The correct choice indicates that frequency relaying should not exceed 50% of the available dynamic reserve. This limitation is important because if the frequency relaying threshold exceeds this percentage, it could potentially lead to system instability. When too much of the dynamic reserve is allocated to frequency relaying, there may not be enough reserve left to address other critical reliability needs, particularly during times of rapid frequency fluctuations.

By keeping the frequency relaying limit to 50%, it ensures that there is always a sufficient cushion of dynamic reserves available to handle disturbances in the grid, thus maintaining the reliability of power supply and preventing outages. This balance helps in effectively managing operational risks and ensuring that the system can respond adequately to changes in demand or generation.