Which action is appropriate when a 500 MW generator fails, causing system instability?

• A. Wait for the generator to come back online.
• B. Open all nearby transmission lines.
• C. Shed Load immediately.
• D. Increase generation at remaining units.

Answer: (C)

Shed Load immediately is the appropriate action when a 500 MW generator fails, causing system instability. This response is crucial in maintaining the balance between generation and load within the power system. When a significant generator goes offline suddenly, there is a gap between the power being produced and the power being consumed. If this gap is not addressed quickly, it can lead to system instability, which may result in cascading failures or blackouts.

By shedding load, operators can reduce the demand side of the equation, thereby stabilizing the grid. This action helps to prevent overloading remaining generators and transmission assets, ensuring that the system can operate within its safety margins. Shedding load is a common protective measure used to avoid more severe consequences from unexpected generator outages.

Other options, such as waiting for the generator to come back online or opening all nearby transmission lines, would not effectively resolve the immediate instability. Waiting would leave the system vulnerable, while opening lines could worsen the situation by further disrupting the flow of electricity and potentially causing additional outages. Increasing generation at remaining units might be part of a longer-term strategy but is typically not sufficient on its own immediately after a large generator failure. Effective load shedding is a proactive step to maintain grid reliability during such incidents.