Explore the vast range of titles available.

This article briefly described the mechanism of transformer magnetizing inrush current, and introduced the principle of differential protection magnetizing inrush current suppression of Siemens 7UT682 protection device. Through the analysis and research of a differential protection malfunction trip event when a no-load closing power of a overhauled transformer, the method of optimizing the relevant parameter configuration of the protection device to avoid the excitation inrush current was proposed and achieved good application results.

In view of the problem of floor water inrush in the process of deep coal seam mining, propose to establish a risk assessment model for coal seam floor water inrush using GIS and combined weight TOPSIS method. Take coal 12-1 of level −950 in Donghuantuo Coal Mine as an example, the coal seam hosting thickness, coal seam burial depth, fault intensity index, aquifer thickness, water-rich aquifer thickness, first aquiclude thickness and second aquiclude thickness are taken as decisive indexes. Based on actual engineering exploration, the entropy weighted AHP weighted TOPSIS method is used to determine the partition threshold and classification level, analyse the risk of water inrush from coal seam floor, and visualise it based on GIS platform. The results show that the combined weight values of coal seam burial depth and fault scale index are 0.4008 and 0.2201, which have a significant impact on water inrush from the coal seam floor. The zoning threshold for the risk coefficient of water inrush from the 12–1 coal seam floor is 0.478, The overall water inrush risk of the mine field is less. Only a few areas in the southwest of the mine field are water inrush risk areas.

Roof water inrush at the mine face and shortages of water resources are both problems in the karst mining area in southwestern China. In this study, field measurements, similar simulations, and theoretical analysis were conducted, a physical model of upward and downward mining in a test mine was constructed, and the dynamic evolution of water inrush and the mechanism of water inrush in karst roofs under different mining sequences were analysed. As a result, the problem of water inrush at the mine face was solved, and a method to utilize the karst groundwater water resources was proposed. The research showed that after downward mining, the maximum development height of the water-conducting fracture in coal seam 4 was 43.1 m, and the fracture mining ratio was 14.4. A water-inrush pathway formed at the connection between the mining-induced fractures and the roof karst aquifers, and the safe mining of coal seams 4 and 9 were threatened by water inrush from the goaf. So, the feasibility of upward mining was determined by the ratio test and \"three zones\" discrimination methods, and the evolution of water-inrush pathways during upward and downward-inclined mining were compared. Upward-inclined mining was proposed to control roof water inrush. Moreover, the quality of the water flowing into the goaf was compared with the Chinese standards for water use, and the water in the goaf of the lower coal group was suitable for water resource utilization. This research provides a basis for preventing and controlling roof water inrush disasters and for appropriate utilization of water resources in these mining areas.

The mechanism of water inrush from the stope floor has always been the key and difficult point in the research field of coal mine water disaster prevention and control. The mechanical essence of water inrush from the mining floor is the loading–unloading stress state transformation process. To reveal the joint action mechanism of principal stress state transformation and water pressure in the process of water inrush from the stope floor, the author studied the water inrush criterion, the characteristics of saturated rock damage test and the characteristics of principal stress transformation of coal floor using theoretical analysis, laboratory test and numerical calculation. Research results: The results show that the threshold of water inrush criterion of the mining floor is 1, based on the discrimination index of disturbance degree of mining floor strata, the threshold of floor cracking pressure, and the instability index of floor aquifer. The damage to the limestone floor samples has an obvious delay effect after pressure relief, but it produces a stress drop phenomenon when it is unstable. The maximum principal stress of the back floor in front of the working face is converted from horizontal stress to vertical stress. After the floor is unloaded, the maximum principal stress is transformed from vertical stress to horizontal stress. The difference between the maximum principal stress and the minimum principal stress of the mining floor presents different distribution characteristics at different depths, but it increases overall and is concentrated near the front and back coal walls of the working face. The research results will help to further reveal the mechanism of water inrush from the stope floor.

Frequent water inrush disasters in deep coal seam mining pose a significant threat to the safety of coal extraction operations. Due to the complexity and non-linearity of water inrush factors, evaluating the risk of water inrush in coal seam floor is challenging and the results can vary significantly. To achieve more accurate evaluations, the weighted rank-sum method and Grey-TOPSIS method were employed, alongside a master control indicator variable-weight model, for assessing the risk of water inrush in coal seam floor. Validation of the evaluation zoning map against actual conditions revealed that both methods produced accurate assessment results, thus affirming the reliability of the new evaluation approach. Compared with the water inrush coefficient method, the diversification of index factors weakened the absolute control effect of the water inrush threshold. The evaluation outcomes were more systematic and comprehensive, providing a new methodology and perspective for deep coal seam mining.

Fault rock is a typical hazardous material of water–silt inrush during the excavation in underground mines. To investigate hydraulic characteristics of fault rock during the water–silt inrush, a one-dimensional radial three-phase flow model of water–rock–silt was established in this study. In the proposed model, the mass conservation and continuity equations of the three-phase flow were obtained; the rock particle migration and the momentum conservation of the three-phase fluid migration were described by erosion constitutive equations and non-Darcy flow equations, respectively. The laboratory tests of porosity and the evolution of volume discharge rate were compared, and the accuracy of the proposed three-phase model was verified by the comparison results. From the test and numerical results, a high standard deviation of repeated results is observed in the case with high silt concentrations, and the erosion effect is inhibited by the silt flow. Last but not least, the temporal–spatial distribution of hydraulic properties is obtained by the numerical simulation: With the progress of the three-phase flow, rock particles near the fluid outlet are first fluidized and constantly migrate outward, resulting in an increase of the porosity and permeability in fault rock. Subsequently, water-conducting pathways are gradually formed inside the fault rock, and then more fluidized rock particles flow out. Finally, the fluidized rock particles have completely migrated, and the porosity and permeability tend to be stable with the more significant non-uniform spatial distribution.HighlightsA one-dimensional radial three-phase flow model of water-rock-silt is established.Mass conservation, continuity, erosion constitutive and non-Darcy flow relations are considered.Laboratory tests are designed to verify the proposed model from porosity and volume discharge rate.Temporal-spatial distribution of hydraulic properties during water-silt inrush is obtained.

The geological hazard of water–sand inrush is a matter of concern for infrastructure construction and resource exploration activities in China, due to the complex interplay between groundwater dynamics and the stability properties of sand particles. This phenomenon is characterized by its intensity, hazardous nature, and unpredictable behavior. Following comprehensive analysis, this study identifies the critical factors influencing water–sand inrush processes as fissure width, water stress (waterhead height), in-situ sand ground stress within the sand stratum, and clay content. To investigate these factors experimentally, a custom-designed hydraulically coupled water–sand inrush test apparatus was used. The apparatus was equipped with a cylinder to apply ground stress, a pneumatic diaphragm pump to regulate water stress, and a bottom opening in the sand layer. Tests were conducted to investigate the dynamic response of water–sand inrush events under various combinations of factor levels. The findings revealed that the critical value for inrush is only present in the fissure width, which was observed to be 3 mm for the tested sand material. Unlike fissure width, the other factors do not have definitive critical values but instead modulate the intensity of the inrush process without determining its occurrence. The ‘inrush rate’ serves as a measure of the severity of water–sand inrush disasters and shows a linear increase with both increasing groundwater stress and fissure width, a negative exponential function relationship between the inrush rate and the clay content. Notably, ground stress does not exert a significant influence on the intensity of the inrush process itself. Under constant conditions, the inrush rate remains relatively constant across different levels of sand ground stress, for instance, in the experiments, the inrush rate was measured at 1.606 kg/s when the water stress was 0.1 MPa and the fissure width was 5 mm. Grey relation analysis was used to examine the sensitivity of each factor’s influence on the inrush rate. The results showed that water stress has the greatest impact on the intensity of water–sand inrush, followed by ground or soil stress, clay content, and the width of the fissures in the sand layer.

After the successful startup of the #2 main transformer at the 110kV Ruixia Substation under no-load conditions, the no-load closing of the #1 main transformer caused an incorrect operation of the distance protection, affecting four protection zones. Through theoretical analysis, it was determined that this issue resulted from the sympathetic inrush current. Additionally, a detailed PSCAD electromagnetic transient simulation model was created to further simulate and verify the event. Based on these simulations, a practical and feasible solution was proposed. This paper presents both theoretical and simulation-based analysis of an actual grid event, offering valuable insights for analyzing similar incidents and preventing their recurrence.

We analyzed the regional nature of China’s coal mine water disasters based on three aspects: the main water source, water-conducting passages, and threat level of water hazards. The development of water hazard control technology in China’s coal mines, including exploration and assessment of hydrogeological conditions, water inrush mechanisms, and predictive technology were all reviewed. We then focused our discussion on the calculation theory and methods behind mine inflow prediction, methods of dewatering and depressurizing, and technology for mining under water pressure and water-blocking grouting. Finally, we present the evolving trend of coal mine water disaster prevention and control technology, which is characterized by accuracy, transparency, environmental considerations, informatization, and intelligent technology.

The residual flux of power transformers is an important factor affecting the inrush current. In order to solve the problem of residual flux measurement of power transformers, this paper proposes an indirect measuring method of residual flux based on the first peak value of inrush current. Through the investigation of the relationship between the inrush current, closing angle and residual flux, the value of residual flux can be measured by measuring the inrush current with controlled closing angle of different conditions, and the accuracy and validity of the residual flux measurement method is verified by experiment.