Study on Inductance Saturation Characteristics of Double-Winding Current-Limiting Reactor

To address the problem of excessive fault currents caused by the continuous increase of short-circuit capacity in power grids, iron-core current-limiting reactors are widely used in engineering practice. However, the nonlinear magnetization of ferromagnetic materials leads to significant inductance saturation under large currents, affecting the current-limiting performance and the accuracy of protection settings. In this paper, a power-frequency double-winding current-limiting reactor small model is investigated. Based on an equivalent magnetic circuit, the winding current, core-yoke flux density, winding leakage flux density, and equivalent inductance are identified as key variables; the concepts of rated inductance, transient inductance, saturated inductance and their corresponding drop ratios are defined, enabling quantitative characterization of inductance droop. A three-dimensional finite-element model incorporating the nonlinear B–H curve of the core yoke is then established in COMSOL Multiphysics, and the operating condition with inner-winding excitation is simulated over a current range of 7.7–126 A. The results show that when the current increases from 7.7 to 126 A (about 16 times the rated current), the maximum leakage flux density around the winding rises from 0.013 to 0.135 T (about 9.4 times), and the maximum flux density in the yoke increases from 0.15 T to about 1.73 T (about 11.5 times). The main magnetic path thus enters deep saturation, the flux is clearly diverted into air and winding gaps, and the equivalent inductance–current curve exhibits pronounced nonlinear droop. An over-saturation impedance test on a double-winding prototype shows that the measured impedance–current characteristic agrees well with the simulation, validating the effectiveness of the proposed model and method. The results provide a basis for parameter selection, structural optimization, and assessment of current-limiting capability of double-winding reactors under extreme short-circuit conditions.