A novel analytical method for prediction of the broken bar fault signature amplitude in induction machine cage rotor and synchronous machine damper winding

In this paper, the rotor failures in squirrel cage induction machines and the damper winding failures in synchronous machines are analytically investigated. The quantitative evaluation of the stator current left sideband component (LSBC) amplitude is discussed and its correlation with the number of broken damper bars is derived. Unlike the cage rotor of an induction motor, the damper bars are often not uniformly positioned on the rotor, causing anomalous emf induced the bar circuits. This makes the diagnostics more difficult because the well-known broken bar signature in the stator current spectrum of an induction machine already exist in that of a synchronous machine with a healthy damper winding. Therefore, detecting the LSBC signal does not necessarily indicate a failure and the diagnosis requires further knowledge about the behavior of the signal amplitude. The bar breakage of a cage induction machine is analyzed first and then it will be expanded to the special case of a damper winding structure. The analytical results are to be compared with the simulation results.