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The present switching speed measurement devices for circuit breakers are mostly low in accuracy， severe on installation conditions， and cannot achieve real-time online monitoring. A new system for real-time switching speed measurement of circuit breakers based on a line array camera is proposed. First， the experimental technique is studied by building an experimental frame simulating the rotation of circuit breakers. A turntable is installed at the output of the motor to simulate the rotating shaft of the circuit breaker actuator， and a line array camera is placed on the turntable side to capture the black and white narrow strip images of the targets set on the turntable. Afterward， the appropriate resolution， exposure time and judgment threshold are chosen to analyze the changes of the images taken by the line array camera in real time to obtain the real-time motion travel of the target and the rotation speed of the turntable. The switching speed of the circuit breaker is obtained to verify the feasibility of the measurement scheme. Finally， it is applied to a pilot substation to monitor the motion travel of the switching of the circuit breaker in real time. Compared with the existing technology， this measurement system can process the images more quickly and measure the switching speed more precisely and stably.

This paper aims to study the influence of the goaf in the upper coal seam on the overlying ultra-thick coal seam and determine the dislocation distance in the roadway layout of the lower coal seam. Based on finite difference method, this research, takig Tashan Coal Mine as the engineering background, established Mohr-Coulomb and double yield constitutive models to invert the rock strata and the rock mass in the caving zone. The failure law of the ultra-thick coal seam under the influence of the overlying close goaf was studied on the basis of goaf and the residual coal pillar. In addition, the distribution law of stress field and the failure range in the coal seam under the goaf were clarified. With the theoretical analysis and the field borehole peep results, the reliability of the numerical method in this paper was verified, and the inner interlocked distance in the roadway layout of the lower coal seam was determined. The results show that the residual coal pillar has the greatest influence on the mining of the lower coal seam. The stress field under the residual coal pillar forms an approximate “normal trapezoid” influence range in the lower coal seam, with the width of the upper and lower being 32 m and 56 m respectively. The plastic zone under the residual coal pillar is distributed in an “inverted trapezoid” in the lower coal seam, and the width of the upper and lower is 81.36 m and 61.47 m, respectively. The inner interlocked distance of the roadways of the lower seam should be 13.5 m.

The advanced deep hole blasting (ADHB) is commonly used to improve the fragmentation of thick hard top coal in longwall top coal caving (LTCC) mining. This paper presents an acoustic method to quantitatively evaluate the effectiveness of the ADHB. First, the variations of P‐wave velocity of hard coal samples under uniaxial and triaxial compression are obtained from the laboratory acoustic test. Then, an acoustic wave method based on seismic tomography is proposed to assess the effectiveness of the ADHB by introducing the P‐wave velocity attenuation model into the data processing. Finally, a field seismic tomography test is conducted to obtain the distribution of the P‐wave velocity of top coal before and after the ADHB implementation. And the P‐wave velocity attenuation is calculated to estimate the fragmentation effectiveness of ADHB. The results indicate that the P‐wave velocity attenuation model could well represent the broken degree of hard coal, suggesting that the proposed acoustic wave method could quantitatively evaluate the fragmentation effectiveness by exporting the nephogram of P‐wave velocity attenuation. The present study may provide technical support for improving the recovery ratio of thick hard top coal for LTCC mining. [ABSTRACT FROM AUTHOR]