[Purposes] In order to achieve turn-to-turn short circuit fault protection of dry-type hollow reactor under harsh and variable outdoor operating environment, a fault detection method based on the rate of change of power factor was proposed.[Methods] Firstly, ANSYS Maxwell was used to establish a finite element field and circuit coupling model of a dry-type hollow reactor and simulate the occurrence of turn-to-turn short circuit faults at different locations in different circles of the reactor, which revealed the change rule of power factor. Then, harmonic analysis was adopted to calculate the power angle. According to the fluctuations in the rate of change of multiple power factors and the different types of faults of the reactor, a turn-to-turn short circuit fault detection method for the dry-type hollow reactor based on the rate of change of power factor was proposed. [Findings] When a dry-type hollow reactor has a turn-to-turn short circuit fault, the rate of change of power factor is large if there are more short-circuited turns. When the number of faulty turns is the same, in the axial direction, as the fault location is closer to the end, the magnitude of power factor increase gets small; in the radial direction, as the fault location is closer to the inner layer of the envelope, the magnitude of power factor increase gets small. In addition, the change in power factor is the most slight when a single-turn short circuit fault occurs in the innermost layer of the coil end, with a value of 6.718 9%. With the effect of noise taken into account, the simulation finds that there are more than 20 locations with a rate of change of power factor exceeding 6.718 9% after fault occurrence, and the number usually does not exceed 20 under normal operating conditions. Therefore, 20 is taken as the protection threshold. Simulation verifies that the proposed fault detection method can correctly identify turn-to-turn short circuit faults at different locations in different circles, greatly improving the operational safety of outdoor dry-type hollow reactors. [Conclusions] The proposed fault detection method in this paper effectively solves the problem that the reactor fault characteristics are weak and difficult to detect in the industry for a long time, and it proves that using the combination of the rate of change of multiple power factors at different time to identify faults is a more effective solution idea, which can provide a reference for the subsequent research.