High-impedance faults (HIF) occur frequently in resonant grounding systems and are difficult to detect. Thus, an effective HIF feeder identification technology is urgently needed. This paper establishes an HIF equivalent circuit in a resonant grounding system. The change rule of transient zero-sequence voltage, transient zero-sequence currents, and their projection components with respect to the transient zero-sequence voltage of the bus are analyzed in both underdamping and overdamping resonance conditions. Furthermore, the variation ranges of the resonant frequency, the magnitude, the attenuation factor, and other parameters are specified in detail. The magnitude and phase relationships of zero-sequence currents among the faulty feeder, healthy feeders, Petersen coil, and fault points, as well as the relationships between their projection components and quadrature components with respect to the transient zero-sequence voltage are analyzed and compared. A novel faulty feeder identification method based on a comparison of the magnitude and polarity of the transient zero-sequence current's projection component is proposed. The accuracy of the transient characteristics and the feasibility of the proposed method are verified by simulations and field data.