What is a critical requirement for a generator that is offline during maintenance?

A generator that is offline during maintenance must maintain certain operational characteristics to ensure that when it is brought back online, it integrates smoothly with the grid. The requirement that it must remain in continuous voltage control until fully operational is critical. This means that even when a generator is offline, it should still be capable of managing voltage levels on the system to ensure stability.

Voltage control is essential for the overall health of the electrical grid, preventing fluctuations that could lead to outages or equipment damage. If the generator is capable of providing voltage control signals or support, it can help stabilize the grid until it is ready to resume full service. This is especially important in areas where there are limited resources or backup systems available.

The other options do not capture the essential criteria for maintaining grid stability during a generator's offline period. For instance, resuming service without checks could lead to potential safety hazards, customer notification during maintenance is typically done by the utility but does not relate to the operational readiness of the generator, and replacement with a backup generator is a separate operational decision that may not always be necessary. Thus, the emphasis on continuous voltage control is paramount for operational integrity and grid reliability.