Ventilation of Revolving-Field Salient-Pole Alternators

The studies were made experimentally and analytically. In the experimental study, a model of hard wood was used, with a multiple of vent ducts of normal width of ¿ in. each in the stator, the slots and teeth being of approximately average width. A four-pole rotor is distinct from one of a large number of poles; consequently two rotors were built, one of four poles and one of twelve poles, the latter being considered as representative of the greater number. The end bells and the imitations of the end windings were different for the two numbers of poles. In the test results given, data for only standard fiber wedges are included, but other forms were investigated. The vent fingers extended the full depth of the core, thereby enabling measurement to be made of the volume of air per vent per tooth, a rotating vane anemometer with a suitable funnel attachment being employed. The end bells were solid, simulating standard construction and the entrances to the two bells were joined to a common duct, in series with which was a thermal volume meter and an external blower, the speed of which could readily be adjusted. (See Fig. 6.) Pressures were measured in the inner and in the outer end bells. The rotor of the model was driven by a d-c. motor, the power input to which was measured. By this means windage damta wwere obtained, and many of those resu≫ lts are included among other data on the curve sheets.