How long can pre-contingency thermal limits be sustained during an emergency?

In the context of transmission system operations under PJM guidelines, the pre-contingency thermal limits refer to the allowable maximum current that a transmission line can carry under normal operational conditions, before any contingencies occur. During emergency situations, such as the loss of a key component or a drastic change in load, operators may allow certain facilities to exceed these limits for a brief duration. This is done to maintain system reliability and prevent wider disruptions.

Sustaining pre-contingency thermal limits during such emergencies, the standard maximum duration is generally accepted in the industry to be around five minutes. This timeframe is critical; it allows operators to manage and resolve the immediate issue—such as redistributing load or activating other resources—without risking damage to transmission infrastructure.

Any longer duration may increase the risk of overheating and potential failures that could arise from prolonged thermal stress on equipment. Therefore, the five-minute duration is a well-established threshold for maintaining operational integrity while giving sufficient time to address the emergency.