No more than what percentage of the total dynamic reserve can consist of load with under frequency relay protection?

The correct answer is that no more than 50% of the total dynamic reserve can consist of load with under frequency relay protection. This limitation is essential because it ensures that there is a balanced and effective response to frequency events in the power system. Load with under frequency relay protection is designed to disconnect in response to frequency drops, which could jeopardize the grid stability if relied upon too heavily.

By limiting the percentage to 50%, this guideline helps maintain sufficient reserves that can be activated without overly depending on these protective loads. It promotes a diverse and robust response strategy to manage frequency fluctuations while ensuring that other forms of reserves, like generation capacity, can provide necessary support during critical situations. Such balance is crucial for maintaining reliability in the power system, particularly in the dynamic environments managed by PJM.