Foundation forces due to dynamic air gap torques of soft mounted asynchronous machines with flexible rotors in sleeve bearings — a calculation method

During line or converter operation dynamic torques in the air gap of asynchronous machines may occur, caused by e.g. faults or by switching operations. The dynamic torques cause dynamic foundation forces, which load the foundation. Therefore the foundation of the machine has to resist these dynamic foundation forces, but also influences the dynamic foundation forces. In this paper a theoretical method is presented - shown at a simplified machine model - for calculating dynamic foundation forces of soft mounted asynchronous machines with flexible shafts and sleeve bearings, which is typical for large 2-pole machines and high speed applications. Using this method, it is possible to optimize the foundation, concerning dynamic foundation forces and vibrations, by choosing suitable foundation stiffness and damping.