Blindagens eletrostáticas para atenuação das correntes nos mancais do motor de indução: análise computacional de sua eficácia e impacto no desempenho do motor

Abstract

The search for efficient electrical drives has allowed the emergence of very fast power switches that are capable to apply steep voltage pulses with high dv/dts (several kV/μs) at the machine terminals. In addition, a common mode voltage is naturally generated at the inverter output and its high frequency components (which are associated to these high dv/dts) excite the parasitic capacitances inside the motor, enabling the circulation of electrical currents. If the machine and/or load bearings are part of their path, such currents can cause serious damage to these components. The inverter-induced bearing currents are classified as: 1) Capacitive currents; 2) Resistive (or conduction) currents; 3) Electric discharge machine currents (EDM); 4) Circulating currents; 5) Rotor ground currents. Different mitigation techniques to eliminate the inverter-induced bearing currents can be found in the literature. These mitigation techniques include the use of filters to reduce common mode voltage and common mode current, insulated bearings, motor shaft grounding, electrostatic shielding installation, among others. With respect to the use of electrostatic shields to reduce the bearing currents, further investigations are needed for its industrial application feasibility. To contribute to this theme, a thorough analysis of the shielding effectiveness to mitigate the undesirable phenomena and its impact on the motor operation was carried out. Employing 2-D and 3-D models, several finite element analysis (FEA) simulations were thoroughly made addressing the shielding effectiveness (SE) to attenuate the bearing currents and the associated eddy current losses for different shield widths, thicknesses, and materials. Furthermore, the possible impacts on the machine operation quantities (such as line current, average torque, and efficiency) due to the shield presence are also evaluated, as well as the SE variation with frequency. The obtained results provide very good guidelines for the practical design of the shielding device.