Because of the incorrect polarity connection of voltage transformer and current transformer in field, faulty feeder selection based on transient reactive power direction leads to wrong easily when there is a single-phase earth fault in resonant grounding system. In this paper, the effect of the incorrect polarity connection of voltage transformer and current transformer on transient reactive power and power-frequency reactive power is analyzed. A novel method using the power-frequency reactive power to correct the transient reactive power for faulty feeder selection is proposed. The faulty feeder is the one which the corrected transient reactive power is negative. If all of the corrected transient reactive powers are positive, it is bus fault. The proposed method is independent of polarity connection of voltage transformer and current transformer, which enlarges the selection scope. The feasibility of the new method is verified by digital simulation and field fault data. This work is supported by National Natural Science Foundation of China (No. 51477184).