Projects : Generator Cooling

A customer had designed a new air-cooled electrical generator but was concerned that the generator might not have enough cooling airflow through the coils to keep the insulation from melting. Generator engineers traditionally use one-dimensional calculations to estimate the cooling airflow rate, but this generator was expected to run hotter than its predecessor, so an error in the airflow calculation could be disastrous.

Alion Science and Technology, a Dynamic Power Technologies Group company, developed a three-dimensional computational fluid dynamics, or CFD, model of the generator cooling air plenum, it’s front wall, and air surrounding the rotor. The plenum is the open space beneath the coil end turns. The generator coils act like a centrifugal compressor and suck in air as they rotate, so the model had to be run using a rotating coordinate system. Furthermore, the engineers had to add both resistance and pumping characteristics to the model coil passages so that the flow distributions would be realistic.

The model results showed that air entered the cooling air plenum stacked to one side with a large separation region at the other side. As air tried to leave through coil passages on the one side, pressure losses increased and more air was forced to go to other passages. The generator only drew in 65 percent of the required cooling air, so compressor vanes were added to the plenum to increase the airflow. Test data later verified the analyses.

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