What is the implication of primary reserves falling below the specified requirement?

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Primary reserves provide rapid, automatic frequency response to disturbances, helping to keep the system’s frequency within safe limits. When those reserves fall below the required level, the system loses that quick cushion, so a disturbance could cause larger frequency deviations and even instability. That situation signals a warning: the grid could be at risk of failure if another event occurs or if reserves aren’t restored promptly. It is not an instruction to shut down all power sources, nor does it imply a mandatory immediate shutdown of operations; nor is there no effect on stability—there is a real risk that requires corrective action to restore adequate reserves.