R. Wieser, C. Kral, F. Pirker, M. Schagginger:
"Sensitive Rotor Cage Monitoring without Frequency Analysis, the Vienna Method";
Talk: speedam, Sorento, Italien; 06-01-1998; in: "Symp. On Power Electronics Electrical Drives Advanced Machines Power Quality", (1998), 1.

Spectrum analysis fault detection techniques rely on constant speed operation and are thus difficult to adapt to variable stator supply frequency. Additionally the high measurement distortion level of PWM drives reduces accuracy. The proposed Vienna Monitoring Method is focused on on-line fault detection for variable speed inverter drives and consequently avoids any frequency analysis. The presented new technique compares two different on-line machine models and derives the fault information out of differences in the estimated machine state variables. Commanded speed and varying load impact on the monitoring method is inherently covered, as both models imply the healthy machine characteristics. The rate of the rotor asymmetry is derived from a spatial deviation analysis in the rotor frame. Although the impact of minor faults on the overall machine behavior is rather small the monitoring scheme is sensitive enough to detect even a single rotor bar resistance increase. At the same time it is highly selective as the information can be derived out of distorted input signals. The technique has been successfully tested for the detection of a faulty rotor bar in an IGBT inverter drive system. Experimental results for both steady state and speed transient operation are presented in the paper.