Detection of Rotor Field Winding, Damper Bar, and Eccentricity Faults in Salient Pole Synchronous Machines with the Pole Drop Test

The pole drop test is the most widely applied means of detecting shorted turns in the rotor field winding of salient pole wound field synchronous machines (WFSM). It is a simple off-line test that relies on detecting the asymmetry between the voltage drop in the windings of each pole with ac voltage applied to the field winding terminals. Although it can provide sensitive detection of shorted field turns, it is also influenced by asymmetries in the motor produced by defects or imperfections in the rotor poles or damper bars. In this work, the feasibility of using the pole drop test for detecting damper bar and eccentricity faults in addition to shorted field windings is investigated for the first time. The change in the impedance of each pole under the fault conditions is analyzed from the electrical equivalent circuit and finite element (FE) simulation. Based on the analysis, it is shown that the 3 faults can be detected and classified from the impedance or voltage distribution with the pole drop test. Experimental tests performed on 4 pole, 30 kVA and 6 pole, 5.5 kVA salient pole WFSMs confirm that the 3 faults can be identified as claimed.