What immediate action is required under the post-contingency transfer limit warning at 95%?

When a system experiences a post-contingency transfer limit warning at 95%, it signifies that the transmission system is nearing its physical capacity and may be at risk of overload if a contingency occurs. The immediate action required is to take steps that manage the reliability of the grid and mitigate potential disruptions promptly.

Thus, marking the response as 'immediate' is crucial because it reflects the urgent need for operators to react without delay. In real-time operational environments, delays could lead to excessive congestion, compromising system reliability, or even leading to outages. It's essential for grid operators to address such warnings instantly to ensure system integrity and maintain a reliable supply of electricity.

In contrast, other options suggesting timeframes like 5 minutes or 15 minutes imply a degree of leeway that does not align with the urgency of an immediate warning. Such timeframes could potentially introduce unacceptable risk to system operations, which is why they wouldn't be appropriate actions in this scenario.