Acoustic resonance in electric machines

A seldom observed phenomenon of acoustic resonance which led to the mechanical destruction of two radial fans in series in a Swiss made synchronous generator at a power plant in India is described in this paper. An axially vibrating impeller along with stiff diffuser acted as a source of pure tones that came into resonance with hydrogen in the cooler, resulting in a fan blow up. It is shown in the paper how some crucial data that help quantify this phenomenon can be restored, knowing no more about construction details of the machine than the Swiss manufacturer published in their advertising brochures.