Characteristics of pressure wave induced by low-energy pulsed discharge in transformer oil

• Plasma-driven shock waves in oil are characterized via low-energy discharges. • Sub-peaks imply secondary energy release but do not change main-peak attenuation. • Quantified attenuation in transformer oil under plasma-dominant conditions. • Higher voltage raises peak pressure and attenuation, larger capacitance raises peak. Internal arcing faults in oil-immersed transformers generate both dynamic and static pressure loads. While quasi-static pressure surges driven by oil vaporization remain the primary focus in tank-rupture assessment, increasing attention has been directed toward the transient shock-wave dynamics generated at arc initiation. A thorough understanding of these early-stage electrohydraulic phenomena requires clarifying the underlying mechanisms of pressure wave generation and propagation in oil. Focusing on the shock wave generated by plasma channel expansion, this work employed low-energy pulsed discharges to limit the influence of oil vaporization and bubble dynamic. Discharges were initiated between needle-needle electrodes, and the resulting pressure waves were recorded using PVDF piezoelectric sensors. Under joule-level discharge energies across different voltage-capacitance combinations, the spatiotemporal evolution of shock waves and the attenuation behavior of their MPa-level peaks were systematically characterized. Results show that the peak amplitude of the plasma-driven pressure wave increases with discharge energy and exhibits a power-law decay during propagation. At fixed capacitance, higher voltage enhances both the peak pressure and the attenuation coefficient. At fixed voltage, increased capacitance primarily raises the peak pressure with limited influence on attenuation. In addition to the expected steep-fronted, Gaussian-like pulse shape, a sub-peak period was observed in several cases. Quantitative analysis shows that the attenuation coefficient of the primary peak lies between 0.747 and 0.803, and the presence of the sub-peak does not alter the attenuation characteristics of the main pressure peak. These findings provide insight into plasma-driven shock waves in transformer oil under limited-vaporization conditions.