Getting the Most Out of the Pole Drop Test for Detecting Rotor Faults in Salient Pole Synchronous Machines

The pole drop test is the most common test applied for detecting shorted turns in the field winding of salient pole synchronous machines (SM). It is a simple off-line test where ac voltage is applied to the field winding, and the asymmetric voltage drop between poles is used as an indicator of shorted turns. However, it is known to have significant risk of giving false indications due to imperfections or defects in the windings, pole, or airgap distribution. Although the test has been applied extensively in the field, the research conducted on the topic is limited. In this paper, new guidelines on testing and interpretation of the pole drop test for improving the sensitivity and reliability of fault detection are presented. An analysis shows that the performance of the test is influenced by the test conditions (rotor in/out, ac/dc voltage) and fault indicator used. Based on the analysis, an insight into how the pole drop test can be performed and interpreted for detecting and classifying field winding, damper bar, and eccentricity faults with maximum sensitivity is provided for improving the reliability of SM fault detection. Experimental results on 5.5 and 30 kVA salient pole SMs are given to support the claims made.