Operating one or more diesel generators without a connection to the electrical grid is known as "island mode" operation. Generators operating in parallel can achieve better efficiency under partial load conditions. Islanded power plants serving isolated communities typically feature at least three diesel generators, with any two of them rated to carry the required load.
Generators can be electrically connected through a synchronization process. Synchronization involves matching voltage, frequency, and phase before connecting the generator to the system. Failure to synchronize prior to connection can result in high short-circuit currents or damage to the generator and its switchgear. The synchronization process can be performed automatically by an automatic synchronizer module or manually by a guided operator. An automatic synchronizer reads voltage, frequency, and phase parameters from the generator and the busbar while adjusting speed via the engine governor or ECM (Engine Control Module).
Load can be distributed among generators operating in parallel through load sharing. Load sharing can be achieved using droop speed control-governed by generator frequency-which continuously adjusts engine fuel delivery to shift load to or from the other power sources. A diesel generator will pick up more load when fuel supply to its combustion system is increased, and shed load when the fuel supply is reduced.
