Synchronizing Devices

Author: E.E. Kimberly

When lamps are used to indicate synchronism, it is not possible to determine exactly when the resultant voltages, as E₁aE₁b, E₂aE₂b, and E₃aE₃b in Fig. 20-10, across the lamps are zero, because these resultant voltages must have some considerable magnitude before the lamps will light at all. The indication of approximation to synchronism afforded by lamps is sufficiently good for small alternators, but large alternators of high speed or large inertia must be synchronized by more accurate devices. For this duty synchronoscopes or synchroscopes have been developed. The synchroscope is essentially a two-phase motor which rotates at a speed equal to the difference in frequencies of the two alternators. The direction of rotation indicates whether the incoming alternator is running too fast or too slow. An indicating pointer attached to the rotating shaft shows when the correct condition for synchronizing is reached. An attempt to synchronize two large alternators with too great displacement error may cause a broken shaft or loosened stator laminations.