As a result of small fault current, high level of noise and a large penetration of distributed generators (DG), in the neutral non-effectively grounded medium-voltage (MV) distribution networks, it is quite difficult to locate the faulted line section for single phase to ground faults. In this paper, using a technique based on synchronized measurements in distribution networks, a fault location method based on the analysis of the energy of the transient zero-sequence current in the selected frequency band (SFB) is proposed. The equivalent impedance of the distribution network with lateral branches is studied with an equivalent network, and the phase-frequency characteristics of the equivalent impedance are analyzed. The SFB, within which the transient energy of the faulty line section is larger than that of the healthy line sections is determined. A combined fault-section location criterion is proposed and the implementation scheme is illustrated with the distribution level phasor measurement units. Numerical simulations of the IEEE 34 node system and the field experiments of a 10kV distribution network validate the feasibility and effectiveness of the proposed method.Index Terms--Active distribution networks, fault location, neutral non-effectively grounded system, single phase to ground faults, transient zero-sequence current.

This study proposes a virtual monitoring method for hydraulic supports based on digital twin theory. This method includes an information model, which monitors the attitudes of the hydraulic supports using an information fusion algorithm. This is combined with a virtual digital model that simulates the actual hydraulic support. Important technological aspects of the monitoring system were achieved at the real-virtual interface, which digitizes and modularizes the management and connection processes of the hydraulic supports over its entire life cycle. Finally, experiments were conducted and the real-time virtual images were synchronized with the actual motion of the support within one second, and the error range between the virtual and actual support postures did not exceed 1%. This study demonstrates the potential of this novel combined approach to make it possible to effectively monitor and make decisions regarding the safe and efficient operation of mechanized mine equipment that employ hydraulic supports.

In a fully mechanized coal-mining face, the positioning and attitude of the shearer and scraper conveyor are inaccurate. To overcome this problem, a joint positioning and attitude solving method that considers the effect of an uneven floor is proposed. In addition, the real-time connection and coupling relationship between the two devices is analyzed. Two types of sensors, namely, the tilt sensor and strapdown inertial navigation system (SINS), are used to measure the shearer body pitch angle and the scraper conveyor shape, respectively. To improve the accuracy, two pieces of information are fused using the adaptive information fusion algorithm. It is observed that, using a marking strategy, the shearer body pitch angle can be reversely mapped to the real-time shape of the scraper conveyor. Then, a virtual-reality (VR) software that can visually simulate this entire operation process under different conditions is developed. Finally, experiments are conducted on a prototype experimental platform. The positioning error is found to be less than 0.38 times the middle trough length; moreover, no accumulated error is detected. This method can monitor the operation of the shearer and scraper conveyor in a highly dynamic and precise manner and provide strong technical support for safe and efficient operation of a fully mechanized coal-mining face.

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The existing automatic control program and its parameters for three machines in a fully mechanized coalmining face are static and simplex and are therefore inadequate for satisfying the complex and dynamic environment of underground coal mines. To overcome this problem, a collaborative mathematical model is established that includes the effects of a dynamic environment. A virtual reality collaborative planning simulator with methods for the three machines is also proposed based on a multi-agent system (MAS). According to the dynamic characteristics of the environment, equipment and technologies, a fully mechanized Unity3D simulator (FMUnitySim) is designed in terms of multiple factors and multiple dimensions. The factors affecting the coordinated operation of the three machines are analyzed and modeled. The communication modes, coordination, and redundant sensing process among multiple agents, which include the shearer agent and the scraper conveyor agent, are also investigated in detail. Using this system, the key parameters of the three machines can be planned and adjusted online to design and distinctly observe the corresponding collaborative simulations of coordinated operation with multiple perspectives and in real time. Tests of different maximum shearer haulage speeds for regular or reverse transporting coal are designed; their key parameters, including the average shearer haulage speed, average follower distance, and average scraper conveyor load, are planned and simulated using FMUnitySim. The optimal parameter combination is obtained by analyzing and comparing the simulation results. The proposed FMUnitySim offers an effective means and theoretical basis for the rapid planning and safe automatic production of a fully mechanized coalmining face.

The scraper conveyor is the key conveying equipment for fully mechanized coal mining. Wear failure of the chute is the main form of failure of the scraper conveyor. In this study, the discrete element method (DEM) was combined with the wear model. The wear mechanism and wear regularity of the chute were explored by tracking the changes in the position of coal particles during the wear process. After the validation of wear simulation, a wear test of coal for different intrinsic parameters was designed. In one wear cycle, the three-body wear was about 32.84 times that of the two-body wear. In the research range, the wear of the scraper conveyor chute increased with the increase of Poisson’s ratio, shear modulus, and density of the coal. The shear modulus showed remarkable effect on the wear of the chute, followed by Poisson’s ratio and density. There existed a linear relationship between the shear modulus and wear (R2 = 0.8232). This study is expected to be used to predict the wear of the scraper conveyor chute and provide a theoretical basis for the applicability of the chute in different mines.

Scraper conveyor is the main equipment for underground coal transportation, and its high-efficiency and smooth operation is of great significance to safety production. This study simulated the process of transporting bulk coal by the scraper conveyor using the discrete element method. Transporting efficiency of scraper conveyor affected by the chain speed, static frictional coefficient, particle size, and laying angle was studied. Then the relationship between the chain speed, static frictional coefficient and the chute wear was explored. The stress and deformation characteristics of the chute during the transportation were studied by coupling the discrete element method and finite element method. Results showed that the mass flow rate changed significantly with the chain speed and static frictional coefficient, while it varied slightly with the change of particle size and laying angle; the higher chain speed and larger bulk coal led to more serious wear of the chute, and large stress mainly concentrated at the direct contact area and the area under the impact load from the bulk coal. Therefore, when designing the chute structure, it is necessary to ensure the wear resistance and strength of the contact area on the chute. The results could provide a theoretical basis for structural optimization of scraper conveyor.

Understanding of material behaviour at nanoscale under intense laser excitation is becoming critical for future application of nanotechnologies. Nanograting formation by linearly polarised ultra-short laser pulses has been studied systematically in fused silica for various pulse energies at 3D laser printing/writing conditions, typically used for the industrial fabrication of optical elements. The period of the nanogratings revealed a dependence on the orientation of the scanning direction. A tilt of the nanograting wave vector at a fixed laser polarisation was also observed. The mechanism responsible for this peculiar dependency of several features of the nanogratings on the writing direction is qualitatively explained by considering the heat transport flux in the presence of a linearly polarised electric field, rather than by temporal and spatial chirp of the laser beam. The confirmed vectorial nature of the light-matter interaction opens new control of material processing with nanoscale precision.