Simulation of Load Short-Circuits Exciting Torsional Resonances in High-Speed Alternators

This paper reports on a research project commissioned by LEONARDO Aircraft S.p.A. to the DAEEE for improvement of diagnostic and protection systems of avionics generators. The arc faults arising in worn brushes and slip-rings supplying the propeller anti-ice rotating loads on board aircrafts are of concern here. Intermittent arc faults may arise, causing current and torque ripples potentially exciting torsional resonances leading to the breakage of the coupling joint (‘mechanical fuse’) between turbine and generator and, hence, to a permanent out of service of the latter. Common non-selective protections are not effective against these types of faults. The study of alternative solutions requires accurate simulations of the complex electromechanical system. This work moves from the construction of the system model, for time-stepping FEM-circuit co-simulations by Maxwell/Simplorer software. Then, fixed-frequency intermittent faults matching experimental tests are analyzed. The causes of failure are definitively determined and solutions to overcome the problem are proposed. A companion paper shows an original online and sensorless method for speed and torque estimation and detection of harmful torsional resonances resulting from intermittent arc faults.