Impact of the Field Winding Interturn Short-Circuit Position on Rotor Vibration Properties in Synchronous Generators

This paper investigates the effect of the field winding interturn short-circuit (FWISC) position on the rotor vibration properties in turbo generators. Different from the previous studies which focused on the influence of the short-circuit degree, this work pays much attention to the impact of the short-circuit position on the rotor unbalanced magnetic pull (UMP) properties and vibration characteristics. The theoretical UMP model is firstly deduced based on the analysis of the magnetic flux density (MFD) variation. Then, the finite element analysis (FEA) is performed to calculate the UMP data. Finally, the rotor vibrations are tested on a CS-5 prototype generator which has two poles and a rated capacity of 5 kVA. It is shown that the occurrence of FWISC will greatly increase the UMP as well as the rotor vibration. In addition to the short-circuit degree, the short-circuit position will also affect the UMP and vibration. The nearer the short-circuit position is to the big rotor teeth, the larger the UMP and vibration will be. The proposed study in this paper will be beneficial for the monitoring and diagnosis of FWISC faults.

Magnetoactive acoustic metamaterials based on nanoparticle-enhanced diaphragm

Magnetoactive membrane-type acoustic metamaterials are fabricated by coating a layer of magnetic nanoparticles on the polyethylene (PE) membranes and their vibration characters are investigated experimentally. From our experiments, we discovered that, under different magnetic fields by varying the distance between a magnet and the membranes, such membranes exhibit tunable vibration eigenfrequencies (the shift towards lower frequencies), which is caused by the variation of the effective mass density and effective tension coefficient resulted from the second derivative of the magnetic field. The strong magnetic force between the layer of magnetic nanoparticles and the magnet enhances the eigenfrequency shift. A spring oscillator model is proposed and it agrees well with the experimental results. We also experimentally observed that the vibration radius, effective mass density, and effective tension coefficient of the membranes can enormously affect the eigenfrequencies of the membranes. We believe that this type of metamaterials may open up some potential applications for acoustic devices with turntable vibration properties.