Which switch must be activated prior to closing the output circuit breaker?

The requirement to activate the synchroscope before closing the output circuit breaker is crucial for the safe and efficient synchronization of power systems. A synchroscope is an instrument that indicates the phase relationship between two AC sources and helps in aligning their frequencies and phases. Before connecting one power source to another, it is essential to ensure that they are synchronized to prevent any potential disturbances or damage to the electrical equipment.

By using the synchroscope, operators can determine if the voltage levels, frequency, and phase angle are adequately aligned, thereby ensuring that the connection to the output circuit can be made safely. If the output circuit breaker is closed without proper synchronization, it could lead to large inrush currents, mechanical stress, or even equipment failure.

In contrast, while the voltage regulator is essential for maintaining voltage levels, and circuit interlocks are meant to ensure safety by preventing certain actions under specific conditions, they do not serve the same purpose regarding synchronization as the synchroscope. The load switch is primarily used for connecting or disconnecting electrical loads but does not play a role in the synchronization process necessary before closing the output circuit breaker. Therefore, activating the synchroscope beforehand is the best practice for ensuring operational safety in power production scenarios.