What happens when the needle of a synchroscope matches the frequencies?

When the needle of a synchroscope matches the frequencies, it indicates that the phase relationship between the two signals or systems being compared is in synchronization. In this state, the needle will complete its movement to the center or neutral position and will stop moving. This stop indicates that the two systems are in sync, meaning they are operating at the same frequency and phase.

In practical terms, when the synchroscope needle is still, it signifies that the generator or incoming power source is perfectly aligned with the grid or existing power system, allowing for a smooth connection without any phase difference that could cause disturbances. Any other scenario—like an increase in speed or reversal of direction—would signify a mismatch between the frequencies, which is not the case when synchronization is achieved.