Dry-type air-core reactor is one of the important equipment in power system

and its failure mode is mainly inter-turn short circuit. It is therefore of great significance to issue effective warning in the early stage of inter-turn short circuit fault. In case of healthy operation of the dry-type air core reactor

the phase difference of voltage and current is a fixed value

and the phase difference changes after inter-turn short circuit. Based on this

a kind of online monitoring method for inter-turn short circuit with phase difference change characteristics is proposed. The field-circuit coupling model of inter-turn short circuit is set up

and the change threshold of phase difference of inter-turn short circuit is set in accordance with the simulation results; SOGI-PLL combined with apFFT algorithm is used to monitor the change characteristics of phase difference in real time. Then

the on-line monitoring system for inter-turn short circuit is set up and its performance is tested. The result shows that the on-line monitoring system can not only find out inter-turn short circuit sensitively

but also measure the phase difference accurately

which meets the requirements of both sensitivity and reliability. The feasibility of inter-turn short circuit monitoring method based on the phase difference change of voltage and current is verified by the research work and a reference for its implementation method is provided.