Analysis of axial voltages and inter-bar currents in cast copper cage rotors during DC current injection as an aid to identify casting faults

In this paper an investigation is carried out to see if it is possible to assess the condition of a rotor by clamping it in a DC-current-injection rig and measuring voltages in bars at regular intervals down the axial length. Experimental measurements are taken on different sections of all the bars for rotors in three different conditions: healthy, with one broken bar at the end, and with all bars broken at each end. A simulation is carried out to compare the results. A complex set of section voltages are found when there are broken bars. There is evidence that this could possibly be a means for testing the condition of rotors, as quality control, during batch manufacturing.