Abstract: Inter-turn arc discharge is one of the most hazardous faults in oil-immersed power transformers, often leading to severe failures such as winding burnout and transformer combustion/explosion. Current understanding of the mechanisms and characteristics underlying the formation and development of inter-turn arcs remains insufficient, and effective detection and early warning methods for the initial stages of inter-turn arc faults are lacking. This paper conducts experimental simulations and multi-physical quantity measurements of inter-turn arc generation and development processes based on a simplified inter-turn model, analyzing the time-domain characteristics and time-frequency distribution features of arc physical signals. The results reveal that the formation and evolution of inter-turn arcs can be divided into four stages: pre-breakdown, repeated breakdown, unstable arc, and stable arc stages. No obvious precursors are observed before inter-turn breakdown, and sustained arc channels require multiple breakdown-recovery cycles to establish post- breakdown. As the arc stabilizes, the channel impedance decreases to 1 kΩ, pulse oscillations disappear, and the time-frequency distributions of acoustic emission and electromagnetic radiation signals become more concentrated. Theoretical analysis indicates that changes in the arc's external characteristics are closely related to parameters of the arc plasma channel, including sheath structure, electron density, and electron temperature.