A survey on statistical indexes applied on frequency response analysis of electric machinery and a trend based approach for more reliable results

•Statistical indexes add more objectivity to FRA results.•A review of statistical indexes applied to FRA is presented.•External factors such as temperature and humidity may induce to wrong diagnosis.•A trend based approach is proposed to mitigate external influence on diagnosis.

This work presents some guidelines in order to achieve a more reliable diagnosis using the frequency response analysis (FRA) technique. Conventionally, this technique relies on comparisons between spectra obtained at different stages of the machine lifespan. A difference between the spectra may indicate the onset of a failure. However, these comparisons are very subjective to the experience of the analyst. To achieve a more objective diagnosis, statistical indexes have been introduced in the literature of FRA. This work presents a survey on these indexes and also compares them using experimental data. Another contribution of this work is the proposition of a trend based diagnostics. Thus, even if the FRA measurements are obtained at different temperatures/humidity or other external factors, the trend curve of the indexes is able to provide a more reliable diagnosis.