One or more diesel generators operating without a connection to an electrical grid are operating in "island" mode. Several parallel generators provides the advantages of redundancy and better efficiency at part loads. An island power plant intended for primary power source of an isolated community will often have at least three diesel generators, any two of which are rated to carry the required load. Groups of up to 20 are not uncommon.
Generators can be electrically connected together through the process of synchronization. Synchronization involves matching voltage, frequency and phase before connecting the generator to a live bus-bar. Failure to synchronize before connection could cause a high current short-circuit or wear and tear on the generator and/or its switchgear. The synchronization process can be done automatically by an auto-synchronizer module. The auto-synchronizer will read the voltage, frequency and phase parameters from the generator and bus-bar voltages, while regulating the speed through the engine governor or ECU (Engine Control Module). Typical manufacturers are ComAp, GAC, Woodward and Heinzman who dominate this market
Load can be shared among parallel running generators through load sharing. Like auto-synchronization, load sharing can be automated by using a load sharing module. The load sharing module will measure the load and frequency at the generator, while it constantly adjusts the engine fuel control to shift load to and from the remaining power sources. As the prime mover of a diesel generator runs at constant speed, it will take more load when the fuel supply to its combustion system is increased, while load is released if fuel supply is decreased.
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