9907-167 WOODWARD

Synchronizing the Generator 

The phase detector compares the two signals and determines any difference 

between the generator and bus phases. When there is a difference, the speed 

bias circuit sends a correction signal to the Load Sharing and Speed Control. The 

correction signal increases or decreases engine speed depending on whether 

the generator is lagging or leading the bus. Correction signal amplitude is 

proportional to the amount of lead or lag (phase difference). 

The phase window, dwell time, and breaker close circuit receive inputs from the 

phase detector. Using signals derived from the generator and bus inputs, the 

phase window circuit checks the phase angle. When the phase angle is less than 

the selected angle (inside the window) the dwell time circuit begins to measure 

the amount of time (dwell) the input signals are in phase and makes sure the 

signals remain in phase during breaker closure. When phase angle and dwell 

time requirements are correct, the breaker closing circuit sends a signal to the 

relay driver/inhibitor. The enable circuit gives a secondary relative phase angle 

check and turns on an indicator. When both the breaker closure circuit and 

enable circuit say the conditions have been satisfied, a signal is sent to the 

breaker closure relay. Then the breaker changes state for about one second. 

Connections for normally open contacts are provided. 

The synchronizer, with or without voltage matching, will not close the circuit 

breaker connecting the generator to a dead bus. If there is no voltage to the bus 

then no correction signal is sent to the Load Sharing and Speed Control and no 

breaker closure signal is sent to the breaker. 

If a dead-bus relay is used to close the breaker, the synchronizer mode switch 

must be in the OFF position until the synchronizer is required to synchronize and 

close the breaker to a live bus. 

Voltage Matching 

The voltage comparator circuit compares the generator and bus voltages. If there 

is a difference, the circuits issue appropriate raise or lower commands to the 

voltage regulator through relay contacts (see Figures 1-3 and 1-4). A voltage 

offset potentiometer (factory set with identical bus and generator inputs) is 

included in the voltage matching circuit to compensate for internal circuit 

differences. This voltage offset should be readjusted only when the bus and 

generator are paralleled. 

The voltage comparator circuit also provides input to the relay driver/inhibitor. 

Any voltage difference between the generator and bus must be within the 

selected voltage range before the close breaker command may be given. 

The voltage matching circuit is disabled when the breaker closure signal is 

issued.