When a generator set is in a paralleled arrangement, the voltage and frequency outputs of the generator sets are forced to the same values when they are connected to the same bus.

 Consequently, generator set control systems cannot simply monitor bus voltage and speed as a reference for maintaining equal output levels, as they do when operated in isolation from one another. If, for example, one set operates at a higher excitation level than the other sets, the reactive load will not be shared equally.

Similarly, if a generator set is regulated to a different speed than the others, it will not share kW load properly with other generator sets in the system. Each generator set in the system always have two active control systems in operation:

The excitation control system regulating voltage, and the fuel control system regulating engine speed.

Generators can be sharing kW load and have problems sharing kVAr load, and vice versa.

Successful load sharing requires addressing of both kW and kVAr load sharing, under both steady state and transient conditions.