Manual 02007
DSLC Digital Synchronizer and Load Control
Woodward
63
Dead Bus Closing
When a dead bus is detected and dead bus closing mode is enabled, the
synchronizer will attempt to get an exclusive lock on permission to issue a
breaker closure command. This security is required to prevent two or more units
from closing their breakers at the same time. To provide this security, a network
message requesting the lock is made to all other DSLC™ controls currently
active on the network.
When a DSLC control receives a lock request, it does the following actions:
1. If a deadbus permission request is not also currently being made, a
deadbus condition is indicated, and the AUX CONTACT discrete input is
inactive (the DSLC control returns a reply message to the requesting unit).
NOTE
The AUX CONTACT open requirement backs up the deadbus condition in
the event of a bus PT failure. If a deadbus condition is indicated by lack of
bus voltage, but the generator breaker is closed, a reply will not be sent.
2. If a deadbus permission request is also being made and that request
sequentially precedes the received request, the received request is
retained, otherwise the reply is sent. (In the event of a sequential tie, the unit
with the lower assigned address wins.)
When all other units have replied verifying that they also indicate a dead bus
(bus input less than 40 Vac L-N) and do not hold a lock, the requesting unit then
holds lock permission and may attempt to close its circuit breaker. The lock is
released automatically after issuing the circuit breaker closure command. This
will allow any other unit to get permission to lock if the breaker fails to close.
The dead bus closing function may be enabled or disabled by the user with a set
point.
NOTE
See Appendix C for compatibility with obsolete DSLC controls when dead-
bus closing is set to Enabled.
Voltage Matching
The voltages of the generators in a parallel system must be matched within a
small percentage to minimize the reactive power flow in the system. If two
synchronous generators of unequal voltage are paralleled, the combined voltage
will have a value different from the voltage generated by either of the generators.
The difference in voltages results in reactive currents flowing in the system with
subsequent lowered system efficiency.
If a synchronous generator is paralleled to a larger system such as a utility, a
difference in voltages before paralleling will not change the voltage of the bus. If
the generator voltage is lower than the bus voltage, reactive power will be drawn
from the bus and used to excite the generator to the higher bus voltage. In the
case where the generator voltage is low enough, the reactive power flow could
motorize the generator with potential damage to the generator windings.