Woodward DSLC, Installation And Operation Manual, Page: 71 / 114

Manual 02007 DSLC Digital Synchronizer and Load Control
Woodward 65
Slip Frequency Synchronizing
In larger systems, it is often desirable for the oncoming generator speed to be
slightly higher than the bus when the generator breaker is closed. This assures
that power immediately flows out of the generator and into the system. The slip
frequency automatic synchronizing function is enabled when the slip frequency
reference set point is set to a non-zero value.
The synchronizer automatically controls the generator at the specified slip
frequency. The DSLC control outputs an error signal to the auxiliary or summing
point of an electronic speed control to provide the correction. Gain and Stability
adjustments to the slip frequency PI controller are provided to allow stable
operation of the automatic synchronizer function over a wide range of system
dynamics.
Synch-check
The synch-check function determines when all conditions for proper
synchronization are satisfied and energizes the breaker closure relay. The
generator and bus voltage comparison is made if the voltage matching function is
enabled. The generator voltage must be within the specified voltage window
above bus voltage before the breaker closure command may be given.
To minimize transients, the breaker must be closed when the phase difference
between the generator and bus is near zero. Due to delays in any interposing
relays and to the delay in closing the circuit breaker, the synchronizer must
initiate the breaker closing ahead of the zero phase point. The control uses slip
frequency and the specified breaker delay to predict breaker closure. The phase
and slip frequency windows provide maximum and minimum conditions on the
prediction. When all conditions of voltage and phase are met, then the breaker
closure command is given.
Multiple Shot Reclosing
The multiple shot reclosing function allows multiple closing attempts. The control
provides set points for the number of close tries and the reclosure delay timing.
Failure to get closure after the specified number of tries locks out the
synchronizer by setting it to the auto-off mode and, if the alarm is enabled, de-
energizing the alarm relay. The synchronizer must then be reset by cycling the
mode switch to off and back to run. The multiple shot closing function is disabled
by setting the reclosing count to one.