Abstract: As a core and critical facility in the power system, the current transformer operates in a multi-physical field coupling environment for a long time. Its internal insulation structure is prone to breakdown under the influence of local strong electric fields, triggering arc discharge in the oil, which causes the insulating oil to crack and expand rapidly, leading to a rapid increase in internal pressure of the equipment. If the pressure cannot be released in time, it is easy to induce a combustion and explosion accident. Therefore, the timely response capability of the pressure relief device under combustion and explosion conditions directly determines the operational safety of the current transformer. This paper focuses on the expander-burst disc pressure relief device of the LVB-220 current transformer, systematically studying its dynamic mechanical behavior and failure mechanism under combustion and explosion impact loads. Based on the explosion test of equivalent hydrogen-air premixed gas, the study focuses on analyzing the temporal characteristics of pressure waves and flame propagation, the deformation patterns of the expander corrugations, and the dynamic opening mode of the burst disc. Combined with ANSYS/LS-DYNA explicit dynamic simulation and using the Johnson-Cook dynamic constitutive model, the study analyzes the entire mechanical response process that is difficult to observe directly in the experiment. The research results showed that in the early stage of combustion and explosion, the pressure wave reaches the pressure relief port before the flame front and triggers the opening of the burst disc. Under high strain rates, the actual opening pressure of the burst disc (0.72 MPa) is higher than the static calibration value (0.2 MPa). The deformation of the expander exhibits characteristics of being large at both ends and small in the middle, reflecting an energy absorption mechanism dominated by low-order bending modes. The asymmetric curling during the burst disc fracture process is closely related to stress wave reflection and fluid-structure coupling induced by high-speed discharge. The numerical simulation and experimental results exhibit good consistency in key dynamic responses. The experimental-simulation collaborative research method proposed in this paper can provide reliable theoretical support and engineering technical guidance for the design optimization of explosion-proof structures for current transformers.