High-speed synchronous machines: A computer system for the study of the effect of rotor radial eccentricity on electromagnetic forces

The problem of the development of modern bearings (magnetic, gas, etc.) for high-speed machines with a wide range of capacities (from tens of kilowatts to megawatts) and rotational speeds (from 6000 to 60000 rpm) used in oil and gas production, robotics, space technology, and mini gas-turbine power plants is considered. The distribution of forces applied to the rotor shaft in different modes of operation is investigated including the case of shaft eccentricity. In operation, the eccentricity should not exceed 5%. A computer system is designed on the basis of the numerical method for field (2D) computation in the active part of the machine. The distribution of forces is analyzed taking into account the saturation of the magnetic circuit of the machine and the harmonic content of the mutual magnetic flux (flux in the gap). When calculating these forces in the no-load mode of operation, it was assumed that, in machines with permanent magnets, the mutual magnetic flux on the rotor is about 10–15% higher than under the rated load because of the demagnetization effect of the armature reaction. The mutual magnetic flux was specified depending on the type of rotor magnets. The computer system takes into account the relative position of the rotor poles relative to the stator field reaction under load (load angle Θ). It is also taken into account that, during use, the resulting mutual magnetic flux is distorted (compared to the no-load mode). As a result, a number of additional high harmonics appear in the gap, which affect the forces applied to the rotor shaft. Load angle Θ is calculated using graphical options of the simulation package by the iteration method. An algorithm for the implementation of this method is described. The distribution of the radial forces along the rotor shaft surface (differential parameter) and the total radial attraction force applied to the rotor shaft (integral parameter) are calculated for different values of eccentricity and different modes of operation of high-speed machines.