Influence of rotor radial ventilation ducts number on temperature distribution of rotor excitation winding and fluid flow state between two poles of a fully air-cooled hydro-generator

With the increase of the capacity of a fully air-cooled hydro-generator, the electromagnetic and thermal designs of such machine face more and more pressure. To ensure the reliability of a large hydro-generator, the thermal issue in rotor should be emphasized. In this paper, the temperature distribution in exciting windings and the fluid flowing between rotor poles are highlighted and investigated. Taking a 250 MW fully air-cooled large hydro-generator as an example, a three-dimensional solid-fluid heat transfer coupling model of the fluid and temperature was established, which includes half-axial rotors, two poles in circumferential direction, and the yoke with four radial ventilation ducts. Via investigating on the loss distribution and the heat transfer condition in the rotor, the fluid and temperature fields of half-axial rotors are calculated by using the conjugated heat transfer method. The obtained results are verified by the measured values. The influences of the velocity and temperature of fluid on its effectiveness of cooling excitation windings, and the relationship between the fluid flow velocity and the heat transferred from outer surface of rotor windings are investigated as well. Similarly, the variations of fluid temperature distribution, the flowing velocity, and the heat transfer coefficient distribution in rotors with two or three ventilation ducts are investigated. The effects of the corresponding velocity and temperature of fluid on temperature distribution within both the windward and leeward side excitation windings are also studied.