New Rotor Fault Indicators for Squirrel Cage Induction Motors

Some new fault indicators for rotor bar breakages detection in squirrel cage induction motors have been theoretically previewed and experimentally proved. They are based on the sidebands of phase current upper harmonics, and they are well suited for converter-fed induction motors. The ratios I_(7-2delta)f/I_5f and I_(5+2s)f/I_7f are examples of such new indicators, and they are not dependent on load torque and drive inertia, as classical indicators (based on lower and upper sideband of first harmonic) do. So, the MCSA technique effectiveness is greatly improved, when applied on motors fed by low switching frequency converters (with natural harmonics) or by high switching frequency converters (with harmonic injection). Applications with grid-connected motors can be studied, too. Motor mathematical modeling was based on the multiphase symmetrical components theory; experimental work was performed by using a prototype with an appositely prepared cage, and successively method validation was achieved on other three industrial motors