Current transformers are core components of power systems used for current measurement and relay protection. During long-term service under coupled multiphysical-field conditions, the internal insulation structure is susceptible to breakdown under locally intensified electric fields, triggering arc discharge in the insulating oil. The resulting oil cracking and rapid gas expansion produce a sharp rise in internal pressure. If this pressure is not relieved promptly, the resulting pressure surge may lead to combustion and explosion accidents. Therefore, the rapid-response capability of pressure relief devices under explosive loading is critical to the operational safety of current transformers. This study focuses on the expander–rupture disc pressure relief assembly of an LVB-220 current transformer and systematically investigates its dynamic mechanical behavior and failure mechanism under explosive impact loading. An equivalent hydrogen-air premixed-gas explosion test platform was constructed. The test system consisted of two stainless-steel flame-acceleration tubes with an inner diameter of 168.3 mm and a total length of 4250 mm, a gas-filling and mixing unit, an ignition device, and a high-speed data-acquisition system. A hydrogen-air mixture with a volume ratio of 27∶75 was used as the combustible gas to reproduce the most severe explosion conditions caused by arc-generated cracking gas in transformer oil. Pressure and flame signals were recorded synchronously using a high-temperature pressure transducer and two flame detectors installed along the tube. The tested assembly consisted of a positive-arch, cross-scored rupture disc made of 316L stainless steel, with a static burst pressure of 0.2 MPa, and a nine-convolution expander. In addition, an explicit dynamic finite element model was developed using ANSYS/LS-DYNA. The Johnson-Cook constitutive model was adopted to describe the strain-rate-dependent behavior of 316L stainless steel. The cross-scored region of the rupture disc was finely meshed with a minimum element size of approximately 0.02 mm to accurately capture crack initiation and propagation. The measured pressure-time history was applied as the loading boundary condition. The model was validated by comparing the simulated opening pressure and expander deformation with the experimental results. The results show that, during the early stage of the explosion, the pressure wave reaches the relief port ahead of the flame front and triggers the opening of the rupture disc. The measured peak pressure before disc opening is 0.72 MPa, which is significantly higher than the static calibration value of 0.2 MPa because of strain-rate hardening, structural inertia, and the spatial nonuniformity of the pressure field under rapid loading. The expander exhibits limited plastic deformation, with the axial deformation of the nine convolutions ranging from 0.60 to 2.30 mm. The deformation distribution is characterized by larger values at both ends and smaller values in the middle, reflecting an energy-absorption mechanism dominated by low-order bending modes. The asymmetric curling of the rupture-disc petals is closely associated with stress-wave reflections and fluid-structure interaction induced by high-speed venting. The numerical simulation reproduces the crack-growth sequence, opening morphology, and stress distribution in good agreement with the experimental observations. The proposed integrated experimental-numerical approach provides a reliable mechanical basis and engineering guidance for optimizing the blast-resistant design of pressure relief devices for current transformers.

This paper systematically reviews the evolution and current state of special fracturing technology. Through comparative analysis of their applicability under various geological conditions, quantitative evaluation of production enhancement performance, and identification of engineering bottlenecks, the study reveals the technical advantages of special fracturing over conventional hydraulic fracturing, particularly in enhancing fracture complexity and controlling reservoir damage. The findings indicate that hybrid fracturing techniques based on energy coupling principles demonstrate significant potential in mitigating stress shadow effects and activating natural fractures in deep reservoirs. To address the current challenges in adapting fracturing technology to deep rock reservoirs, this paper proposes the development of a geoscience-engineering integrated special fracturing system. By integrating multi-physics coupled numerical simulation, intelligent materials, and real-time monitoring technologies, a "green and efficient" fracturing technology matrix tailored to various reservoir characteristics can be established, thereby providing a systematic solution for the safe and low-carbon development of unconventional natural gas resources.

In order to successfully demolish two brick chimneys and two reinforced concrete chimneys located in the same plant area where is a complex environment by blasting. The overall blasting scheme of “single cut, directional collapse” is determined to demolish the four chimneys at one time, by analyzing the surrounding environmental conditions and the structural characteristics. According to the engineering experience, it is determined that the bottom edge of the chimney cut is at the elevation of +0.5 m, the cut angle is 215°, the cut height, cut length and relevant blasting parameters are calculated by theoretical formula. The cut form is trapezoid like, and the initiation network uses the digital electronic detonator initiation system with higher accuracy to initiate in the way of parallel firing. Considering the different structural composition of the four chimneys, corresponding pretreatment schemes are formulated respectively. Through the safety check of the collapse reliability, blasting vibration and collapse vibration of the chimneys and the effective control of the flying debris and flying stones after blasting, the four chimneys collapse in the design direction and prevent harm to the surrounding protection targets. By using the finite element software LS-DYNA to simulate the collapse process of four chimneys, the results show that the simulated collapse process is almost the same as the actual process, and the collapse completion time is around 14 s. Moreover, by analyzing the displacement and velocity law of the top node, it can be judged that the chimney collapse effect is sufficient and the expected goal is achieved, which further shows a guiding significance of the numerical simulation for engineering practice and can provide reference for similar projects.

Methane in-situ explosion fracturing of shale is a revolutionary technology that utilizes the methane analyzed from shale reservoirs and the input combustion aids to carry out explosion reactions, thereby forming a three-dimensional fracture network in in-situ fracturing of shale reservoirs. This study conducted explosion experiments to investigate the variation patterns of key parameters of explosion (i.e. explosion pressure, explosion speed, rise time of peak pressure). We obtained the attenuation patterns of stress wave in shale reservoir through dimensionless analysis. We used the finite element software ANSYS/LS-DYNA to establish models of different working conditions for analyzing the number of cracks and damage evolution patterns of shale caused by explosion. Results show that: 1) The pressure during the methane/oxygen explosion is about 30 times the initial pressure. The rise time of peak pressure is 85 μs. 2) Peak stress of the stress wave and the specific distance in the shale reservoir under the explosion load are exponentially related. 3) The increase in loading rate could form multiple cracks around the explosion hole. 4) Compared with open hole completion, the presence of casing reduces the pressure near the wellbore wall, causing type Ⅰ cracks to extend along the initial fracture direction. The perforation length after extension increasesby 47 % compared to the original length.

To carry out deep coal mining safely and efficiently, the dynamic mechanical characteristics and fracture mechanism of coal rock in deep earth were investigated under the ‘three high and one disturbance’ environment. A dynamic impact test of coal rock was carried out using the self-improved ϕ 50 mm high temperature synchronous split Hopkinson pressure bar(SHPB) test equipment at temperatures between 25~200℃. A ZWT viscoelastic constitutive model was also improved to establish a dynamic constitutive equation considering the temperature effect. The influence of high temperature on crack development law and the dynamic strength of coal rock was investigated based on the coupling of the finite difference and discrete element methods. The results show four stages to the dynamic stress-strain curve of coal rock under high-temperature impact: compaction, elastic, crack propagation, and softening failure. The dynamic compressive strength and dynamic elastic modulus of coal rock significantly decrease as temperature increases. In contrast, the failure strain increases, and the absorbed energy varies in a W-shaped pattern. The fractal dimension increases linearly as the particle size decreases. The degree and complexity of the fragmentation mechanism increase as the compressive strength decreases. Although the improved dynamic constitutive model based on ZWT could adequately express the stress-strain relationship following a high-temperature impact, it does not apply to the compaction stage. According to the simulation and test results, water and adsorbed gas actively escape in the coal rock at 150℃. The coal matrix is also heated and expanded, which induces cracks. There are apparent mesoscopic cracks initially and gradually developed through cracks, mainly shear ones. The crack development of coal rock under dynamic compression at 100℃ develops through the impact surface, and the high temperature deteriorates the strength of coal rock.

The reasonable selection of the incision angle is an important factor for the success of blasting demolition of a typical reinforced concrete chimney. In order to determine the selection range of incision angle, the isolation method was adopted to establish a theoretical model according to the force and failure characteristics of the residual section. The solution formula of any angle position on the residual section was derived, and a revision coefficient k was defined to express the influence of the cylinder at the upper part of the unnotched section. Furthermore, the stress and bending moment conditions of the dumping cylinder were established, and the selection range of the incision angle was obtained by combining the solution formula and the damping conditions. The case study shows that with the increase of the incision angle, the maximum tensile stress, the maximum compressive stress and the bending moment generated by the upper cylinder of the incision tend to increase, while the resistance moment of the residual section tends to decrease. The upper limit of the selection of the incision angle can be obtained when the maximum tensile stress reaches to the material strength limit, and the lower limit can be determined when the two bending moments are equal. Changing the incision angle would have a greater effect on stress than changing the incision height. Under the condition that the actual incision height is 4.5 m in the engineering case, the selection range of incision angle based on the established theoretical model is 198°~237.6°, and the actual incision angle is 216° within the theoretical selection range, which further verifies the reliability of the theoretical model. More extensive application and guide engineering practice are expected.