engleski

Separating Inherent Asymmetries from High Sensitivity Rotor Bar Fault Indicator

Inverter operation significantly reduces sensitivity of rotor bar detection methods based on current signature analysis (CSA). Considering the high frequency and transient electrical properties of the machine a very sensitive detection was proven possible by different authors recently. These methods apply high frequency or transient voltage signals to the machine terminals using the inverter and measure the current reaction. For on-line detection however these high frequency and transient electrical properties are usually superposed with inherent asymmetries like slotting or spatial saturation. To ensure a fault detection in all operating states and to keep sensitivity high the flux/load dependencies of these inherent asymmetries have to be identified during a pre commissioning procedure using for example neural network approach. After this procedure an accurate compensation is possible in all operating states. In this paper a measurement and signal processing chain is described to directly separate the different inherent asymmetries from the fault induced asymmetry without pre commissioning. This signal processing chain is based on repetitive data sampling during normal operation of the drive and applying a set of Fourier transforms. Measurements on a special manufactured machine are presented. The cage of the test rotor allows a single replacement of each individual bar thus enabling to investigate the effect of even partially broken bars. Measurement results prove the efficiency of the proposed method to accurately eliminate the inherent asymmetries caused by slotting and spatial saturation in various points of operation.

AC motor drives; Discrete Fourier transform; Fault diagnosis; Harmonic analysis; Induction motor protection; Monitoring; Pulse width modulated inverters; Squirrel cage motors; Switching transients; Transient response

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