Leakage flux detection of excitation winding inter-turn short circuit of pumped storage unit

The leakage magnetic field at the back of the stator core of pumped storage units can effectively reflect the operating condition of the excitation winding. The leakage flux characteristics of the excitation winding before and after the inter-turn short circuit were investigated in order to achieve online monitoring of its inter-turn insulation health level. Firstly, the expressions for the leakage flux in the healthy and inter-turn short circuit states of the excitation winding were derived, and the characteristic harmonics of the flux density corresponding to the different states were obtained. Secondly, a two-dimensional finite element simulation model of pumped storage unit with a generating capacity of 278 MVA was built, according to which the changes of radial and tangential leakage flux time / frequency characteristics before and after the inter-turn short circuit fault were analyzed. The peak values of radial and tangential leakage flux density are 111 and 102 μT for no-load condition, and 115 and 112. 5 μT for load condition respectively, which can provide a reference for the selection of magnetic sensors. Finally, by installing fluxgate sensor on the back of the stator core of synchronous generator, the radial, tangential and axial leakage flux signals are collected at different levels of inter-turn short circuit, and the peak values are 51. 9, 40. 4 and 28. 2 μT for no-load condition and 56. 5, 47. 3 and 38. 4 μT for load condition respectively. The experimental results demonstrate that the characteristic waveforms in the time domain and the characteristic harmonics in the spectrum can effectively characterize the inter-turn insulation health level of the excitation winding, which expands a new technical path for monitoring the inter-turn short circuit condition of the excitation winding. © 2024 Editorial Department of Electric Machines and Control. All rights reserved.