As the rotor of an electric generator rotates, its magnetic field revolves in unison with the rotor. This rotating magnetic field exerts a cyclical force on the generator's stator core. This force, in turn, causes vibrations to occur in the core which are of concern in high speed, high power machines. The stator core of a machine having a two-pole rotor experiences an elliptical deformation that follows the rotation of the rotor during operation, with resulting vibrations that are at a frequency twice that of the rotational speed of the rotor. The cyclical vibrations will be transmitted through the frame to the generator foundation. The magnitude will depend upon the degree of isolation incorporated in the design.
It is known in the art to utilize spring plates to resiliently support a stator core and stator core frame. For example, U.S. Pat. No. 2,320,843, issued to Baudry on Jun. 1, 1943, incorporated by reference herein, discloses a stator support structure made from flat plates mounted tangentially to the perimeter of a stator core frame. The support structure of Baudry includes a pair of vertical spring plates mounted to the perimeter of the stator core frame along opposed sides of the frame. These vertical spring plates are placed into compression by the dead weight of the generator stator and frame. Due to the geometry of the plates, they are rigid in the vertical (compression) direction, but are relatively flexible in the horizontal (bending moment) direction. Additional horizontal spring plates are attached to the perimeter of the stator core frame along its bottom. Due to the geometry of these plates, they provide rigid support in the horizontal (compression) direction, but are relatively flexible in the vertical (bending moment) direction. Together, the vertical and horizontal plates provide rigid vertical and horizontal support for the generator, while at the same time providing a degree of flexibility to accommodate radial vibrations of the stator core. During its operation, an electric generator may experience a short circuit or other abnormal operating condition. Although the prior art support design performs well in isolating the radial vibrations generated during normal operation of the generator, it is less effective in reducing the tangential torque transmitted to the foundation during short circuit conditions. During these irregular operating conditions, an electric generator may experience torque loads as high as twenty times, or more, the normal operating torque. This large torque amplification mandates a very robust support structure, which in turn tends to reduce the desired flexibility in the radial direction.
The object of the present invention, therefore, is to provide an electric generator having a support system that is capable of providing the necessary support in both the horizontal and vertical directions while providing sufficient flexibility in the radial direction to dampen rotating force loads, and further to provide sufficient strength and flexibility in the tangential direction to accommodate short circuit and off-normal operating torque loads. It is a further object of this invention to provide an electric generator having a support system that functions to isolate the foundation from the radial vibration forces generated during normal operation and from the tangential forces generated during short circuit and other abnormal operating conditions.