The technique also enables engineers to identify problems with the circumferential flow. Previously, the only way to do this was to measure discrete temperatures during a running test. This is too expensive and time-consuming for use in production testing and can only be done after the rotor has been designed and manufactured. By contrast, the hot-film anemometer technique can be performed as part of the factory rotobalance without adding significant cost to the generator.

This technique was used in designing the Westinghouse air-cooled generator (WESTAC). WESTAC's ventilation system reduces overall ventilation flow by 50 percent compared with previous air-cooled models by adopting an axially cooled stator core. This improves the ventilation of the field winding by allowing the air gap to be used exclusively for rotor discharge air.

The result is a lower back-pressure in the gap, which increases field-winding airflow and eliminates the need for radial vents in the stator core. The technique was also used to verify the ventilation of each generator rotor during season and balance before installation.

The above was adapted from an article by W. Ray Laster, a senior design engineer at Westinghouse Electric Corp.'s Power Generation Technology Division in Orlando, Fla., and George W. Sanford, a product design engineer at Westinghouse in Charlotte, N.C. The full text can be found in the October 1996 issue of Mechanical Engineering magazine. ©1996 ASME International. To obtain a copy of this issue, click here.

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