What is the specified duration for normal voltage limits during pre-contingency?

The specified duration for maintaining normal voltage limits during pre-contingency conditions is typically set at 15 minutes. This duration is critical because it allows the system to remain stable and within acceptable operational parameters before any disturbances or contingencies occur. The stipulated time frame is important for ensuring that any temporary fluctuations in voltage, which may arise due to operational changes or load variations, can be mitigated without causing significant disruptions or the risk of cascading failures in the electrical grid. Adequate time is necessary for system operators to assess and respond to the conditions effectively, allowing for the proper management of the grid's reliability and safety.

In contrast, the other durations mentioned would not align with the standard requirements outlined for voltage stability during pre-contingency scenarios, which necessitate a more extended period to ensure proper monitoring and control.