Sensitive Detection of Shorted Field Winding Turns in Salient Pole Synchronous Machines With High Frequency Pole Drop Test

The pole drop test is the most widely accepted test for detecting short circuits in the field winding of salient pole synchronous machines (SPSM). Although it is a simple and effective test, there are concerns on the reliability due to the inherent asymmetry between the poles, especially for cases where the percentage of shorted turns is low. Considering that this is the primary test used in industry for detecting shorted field turns in SPSMs, improving the sensitivity of the test is highly desirable for reliable fault detection. In this paper, it is shown that the sensitivity of the pole drop test can be significantly improved by increasing the excitation frequency of the test voltage above the 50/60 Hz currently used, which is not reported elsewhere. An electrical equivalent circuit analysis and an experimental study on a 4 pole, 30 kVA synchronous motor and a 14 pole, 100 kVA hydrogenator prototype are given to verify the claims made.