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What Are Circulating Currents in AC Generators?

Alexis Writing

During the operation of electrical generators that generate alternating current, as opposed to direct current, current can circulate. This current circulates in much the same way as a current would in a river or water situation, moving back and forth between the two generator fields. Understanding how circulating current operates, knowing what conditions can cause it to be more or less prevalent, and understanding how to mitigate the effects of circulating current, are important in generator set design as well as in the placement and synchronization of generators.

Multiple Generators

Circulating current occurs only if there is more than one generator operating at the same time. If you operate a single generator, there is no where for the current to circulate out of the generator. As a result, the issue of circulating currents is not relevant in setting up a single generator system. Whenever two or more generators are operating in synchronization, however, there exists the possibility of circulating current.

Circulating Currents Travel a Certain Particular Path

There is a particular path by which circulating currents can travel between generators that are operating as part of a group. In general, circulating currents leave the line leads of the first generator, move through the parallel bus of the second generator and come back into the second generator. A circulating current will never enter a generator through the load side of the generator, because there is too much existing current, or electrical flow, through the load side as a result of the generator output. Just like with the flow of water, circulating currents will move in the path of least resistance.

Circulating Currents Can Travel Differently Through Many Generators

If there is more than one generator that has been set up, the circulating current does not travel the certain particular path that it must follow with only two circuits, but may travel through a variety of paths. This can cause problems for electrical engineers and site managers determining where these additional amps and current are coming from. This can be the cause of a dangerous condition.

Circulating CurrentsCause a Variety of Problems for Electrical Circuits

Circulating currents can cause wires or generator parts to overheat because they are not designed for the excess current flow created by these rogue currents. Circulating currents can also cause breakers to trip or fuses to blow; this can lead to operational down time as the circulating current overpowers the circuit in which it has traveled.