The fifth-generation (5G) communication systems will enable enhanced mobile broadband, ultra-reliable lowlatency, and massive connectivity services. The broadband and low-latency services are indispensable to public safety (PS) communication during natural or man-made disasters. Recently, the third generation partnership project long term evolution (3GPP-LTE) has emerged as a promising candidate to enable broadband PS communications. In this article, first we present six major PS-LTE enabling services and the current status of PS-LTE in 3GPP releases. Then, we discuss the spectrum bands allocated for PS-LTE in major countries by international telecommunication union (ITU). Finally, we propose a disaster resilient three-layered architecture for PS-LTE (DR-PSLTE). This architecture consists of a software-defined network (SDN) layer to provide centralized control, an unmanned air vehicle (UAV) cloudlet layer to facilitate edge computing or to enable emergency communication link, and a radio access layer. The proposed architecture is flexible and combines the benefits of SDNs and edge computing to efficiently meet the delay requirements of various PS-LTE services. Numerical results verified that under the proposed DR-PSLTE architecture, delay is reduced by 20% as compared with the conventional centralized computing architecture. II. EVOLUTION OF TETRA-BASED PUBLIC-SAFETY NETWORK AND RELATED WORKSRecently, there has been growing interest in improving communication technologies for PS networks and the existing TETRA-based systems. The major motivation is to provide PSC services till the completion of the evolution phase from the TETRA to the LTE. The evolution plan in Europe, specifically Finland, has five main steps to completely implement hybrid networks that could achieve almost similar performance like broadband LTE for emergency communication services. These steps are: 1) a mobile virtual network operator (MNVO) set up to meet increased data rate requirements. For this purpose, initially, the externally available broadband services will be used for PS services which will be replaced by the LTE core in the future, 2) critical content will be served arXiv:1809.09617v2 [cs.NI]
Abstract-The topology of grounding grid is important for diagnosing its status, which plays a critical role in the safety of personnel and stable operation of power system. The electromagnetic field method and derivative of surface magnetic flux density on the line has been used to measure the branch position in case the grid is parallel to the plane of earth surface that in practice is unknown while the node points and connections were not discussed. This paper introduces a method that uses derivative of surface flux density on circles and lines in a systematic order to find the position of the grid in the plane of the earth surface and connecting the nodes to measure the full topology. This method even identifies any angled branch present in the mesh of a grid. Software simulations and experimental tests verify that the method is feasible and can be applied to identify the topology of a grounding grid.
Abstract-Grounding grid is responsible for driving lightning and short circuit currents into ground. Faults in substation grounding grid can lead to significant rise in surface potential and ultimately loss to power system and operators. This paper proposes a novel technique based on derivative method to diagnose breakpoints in grounding grid. Derivative of surface magnetic flux density on circle results in peak at conductor's location. Once a conductor is broken the flow of current and surface magnetic field ceases, which is recognized by the absence of peak at corresponding conductor's location. The use of circle even enables this method for diagnosing diagonal branch. Furthermore, the method is analyzed for soil of different resistivities and monolayer and multilayer soils. Simulation results show that the proposed method is feasible for breakpoint diagnosis of grounding grid without excavation.
The grounding grid is a key part of substation protection, which provides safety to personnel and equipment under normal as well as fault conditions. Currently, the topology of a grounding grid is determined by assuming that its orientation is parallel to the plane of earth. However, in practical scenarios, the assumed orientation may not coincide with the actual orientation of the grounding grid. Hence, currently employed methods for topology detection fails to produce the desired results. Therefore, accurate detection of grounding grid orientation is mandatory for measuring its topology accurately. In this paper, we propose a derivative method for orientation detection of grounding grid in high voltage substations. The proposed method is applicable to both equally and unequally spaced grounding grids. Furthermore, our method can also determine the orientation of grounding grid in the challenging case when a diagonal branch is present in the mesh. The proposed method is based on the fact that the distribution of magnetic flux density is perpendicular to the surface of the earth when a current is injected into the grid through a vertical conductor. Taking the third order derivative of the magnetic flux density, the main peak coinciding with the position of underground conductor is accurately obtained. Thus, the main peak describes the orientation of buried conductor of grounding grid. Simulations are performed using Comsol Multiphysics 5.0 to demonstrate the accuracy of the proposed method. Our results demonstrate that the proposed method calculate the orientation of grounding grid with high accuracy. We also investigate the effect of varying critical parameters of our method.
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