3angles Non Destructive Testing
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Bump Test of Generator Stator End Windings
One of the tests to assess the condition of generator stator end windings is the performance of a bump test. Bump testing analyzes the natural response of stator end-windings upon excitation from a mechanical impulse.
The conductors, the bars and the complete stator end windings can be considered as a mechanical spring-mass-damper system, and therefore all have specific natural frequencies that depend on the rigidity, mass and damping. Since the windings and supports largely determine the rigidity, the height of the resonant frequency is dependent on the rigidity of the winding or support structure.
Over time the insulation and supports can become loose and the natural frequency can become lower. With the results of bump testing, specific areas of concern can be accurately identified and the overall response plotted. Corrective actions can be taken to avoid an entire rewind of the generator stator, thereby saving considerable amounts of time and money.
The bump test equipment includes tri-axial piezo-electric accelerometers, an impact hammer with a force transducer, data acquisition device and custom software to acquire stimulus and response signals to perform frequency response functions. The inspection program typically includes (1) dynamic flexibility measurements, (2) modal measurements and analysis and (3) phase connection measurements.