Abstract: Excitation winding inter-turn short circuit fault is a common occurrence in large turbo-generators, and prolonged operation under such a fault may lead to more severe consequences. While installing magnetic flux detection coils inside the machine can effectively identify the fault, some generators are not equipped with such devices during assembly, making subsequent installation challenging. Therefore, this paper adopts a non-invasive detection coil placed outside the machine to detect stray magnetic flux, analyze its fault characteristics, and determine the fault. Due to the scarcity of actual fault data, a finite element simulation model is established to simulate the fault and validate the effectiveness of this detection method.