Bearing Fault Detectability in Squirrel-Cage Induction Generator at Different Load Levels via Vibration Envelope Analysis

Squirrel-cage induction generators (SCIGs) have been historically employed as fixed-speed wind generators with direct connection to the grid. With the rapid evolution of power electronics, variable-speed wind turbine systems have become popular and SCIGs are still favored in many applications because of their established maturity and low cost. Despite their higher ruggedness compared to other types of wind generators, SCIGs can undergo different types of fault, which can be potentially accelerated by harsh environmental conditions of operation. Since a major share of machine faults are due to localized bearing defects, much research effort has been devoted to their detection. Typically, the diagnostic procedure is validated under constant speed and load conditions, while less contributions address the detection problem for variable load and speed. In this paper, the efficacy of bearing fault detection via envelope analysis on vibration signals from a small squirrel cage induction generator for different levels of load and speed is evaluated. To this end, a small-scale experimental setup is configured, and vibration signals are acquired for required post-processing. The results obtained under different operating conditions are discussed and compared.