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This paper presents a novel bolt looseness detection method for power transmission towers based on vibration signal analysis. The proposed method utilizes pulse excitation to extract the vibration signal of the tower, which is then adaptively decomposed using the Variational Mode Decomposition of Spider Wasp optimizer (SWVMD). This overcomes limitations of traditional Variational Mode Decomposition methods by leveraging bio‐inspired optimization to improve signal decomposition. Simulated signals processed with different optimization methods verify the superiority of the SWO approach. Field tests on a 110‐kV transmission tower further demonstrate the effectiveness of the proposed SWVMD technique for analyzing on‐site vibration data. A new improved intrinsic multiscale sample entropy feature is also introduced for bolt state characterization. A Spider Wasp Support Vector Machine classifier is developed to realize accurate bolt loosening monitoring using the extracted features. Dynamic response tests under varying bolt conditions show that the method can identify early loosening and reduce tower damage risks compared to conventional techniques. This novel vibration‐based detection framework presents an innovative application of nature‐inspired computing for power infrastructure health monitoring. [ABSTRACT FROM AUTHOR]

In this paper, the initial stage and the return stroke current waveform parameters of rocket-triggered lightning flashes to the ground and to the distribution line have been analyzed. The results show that the average current, the charge transferred and the action integral associated with the Initial Stage with return strokes are greater than the corresponding values without return strokes. For the initial stage, the presence of the distribution line greatly reduces the maximum current, average current, charge transfer, and action integral by a factor of 0.35, 0.42, 0.51, and 0.19, respectively. For the return stroke, the presence of the distribution line has little effect on the other parameters except for a 2.4-fold increase in the 10-90% risetime. The presence of the distribution line affects the initial stage parameters more significantly than the return stroke parameters, probably because the lightning channel equivalent impedance of the initial stage is much smaller than that of the return stroke. The lightning channel equivalent impedance of the initial stage estimated in this paper is about 145 ohms and the estimated lightning channel equivalent impedance for the return stroke is greater than 2000 ohms. [ABSTRACT FROM AUTHOR]

This paper presents an asset health index (HI) prediction methodology for high voltage transmission overhead lines (OHLs) using supervised machine learning and structured, unambiguous visual inspections. We propose a framework for asset HI predictions to determine the technical condition of individual OHL towers to improve grid reliability in a cost-effective manner. The paper focuses on asset HI prediction and the selection of the most parsimonious model. Based on the technical specifications and HI data, our methodology allows for the prediction of a HI for OHLs without HI data, and models asset aging behaviour. Technical specifications and the HI as defined in this paper are taken from the Estonian TSO periodical visual inspections implemented in 2018. The case study successfully demonstrates that the proposed methodology can predict tower HI values for a single OHL with nearly 80 percent accuracy without the need for additional measurements. [ABSTRACT FROM AUTHOR]

This paper discusses the back-flashover (BFO) phenomena in a high-voltage (HV) vertical double-circuit transmission line by means of numerical simulations. The single- and multiphase BFOs are analyzed considering 24 cases of AC-voltage angles and nonlinear characteristic of flashovers, taking advantage of the circuit analysis method in time domain. The models used in circuit analysis are the TEM-delay model, which can take into account the non-TEM characteristics of tower and line, and the conventional models. Prior to the BFO analysis, the characteristics of circuit models are compared and discussed with the numerical electromagnetic analysis results. In BFO analysis, it is clarified that the occurrence probability of the multiphase BFO is heavily depending on the bias AC-voltages. The relation of measured BFO phases and AC-voltages are well explained by the TEM-delay model with the valid lightning current magnitude. The conventional circuit models could have underestimated the occurrence of BFOs in HV transmission lines. The analysis and discussions shown in this paper can be utilized for advanced evaluation of lightning performance of transmission lines that considers the seriousness of lightning accidents. [ABSTRACT FROM AUTHOR]

It is well known that for high voltage transmission lines in the range of 245 kV–525 kV, particularly in regions of high ground resistivity, lightning back flashover problems could be a major concern. Line arresters have been used successfully to address the problem. Underbuilt ground wires have been proposed as a viable alternative. The present paper shows that the full potential of additional ground wires could be achieved by optimizing their position on the tower. Such optimization often results in a preferred position at the level, or higher than the attachment height of the lower phase conductors; therefore the designation Embedded Ground Conductor. An essential requirement is that such positioning does not infringe in any way on the dielectric integrity of the electrical clearances and, under the influence of induced charge, does not become a source of positive streamers that may lead to additional radio or audible noise. It is found that a streamer- inhibited conductor, when properly placed, fully satisfies the above requirements. It is determined that for 245 kV, 345 kV and 420 kV lines, a streamer-inhibited embedded conductor could improve the back flashover rate by a factor of 10 or more [ABSTRACT FROM AUTHOR]

In actual line-commutated converter based high- voltage direct-current (LCC-HVDC) projects, multiple HVDC transmission lines are usually installed on the same tower to save transmission corridors and reduce construction costs. However, electromagnetic coupling effect between adjacent lines can cause commutation failure (CF) in the non-fault poles when a line or pole fails. Hence, this paper deeply investigates the mechanism and the prevention strategy of CFs caused by line coupling effect in single- and double-circuit HVDC systems. The influencing factors of line coupling effect and the coupling characteristics under fault conditions are analyzed first based on the modeling of parallel transmission lines and the traveling wave theory. Then the mechanism of CF caused by line coupling effect is investigated with the consideration of different fault conditions, different line structures, and different system operation modes. Based on the above analyses, prevention strategies for CFs of non-fault poles in single- and double-circuit systems are proposed. Finally, the simulation results verify the correctness of the theoretical analyses and the effectiveness of the proposed control strategies. [ABSTRACT FROM AUTHOR]

The tension insulator string is an important component for transferring the load of the conductor to the transmission tower. The damage of tension insulator strings may dramatically affect the operation safety of the grid power. In this paper, the dynamic response and fatigue life of the tension insulator strings under stochastic wind were systematically studied. Firstly, finite element models of conductors and the tension insulator string upon the actual transmission lines were established. The effects of height difference ratios on the dynamic tension of conductors and the dynamic response of tension insulator strings under a 10 m/s stochastic wind were investigated, respectively. Secondly, a simplified calculation method of stress time history is proposed to simplify the fatigue life analysis for tension insulator strings. Finally, based on the Rayleigh distribution, wind farms with the annual mean wind speed of 7 m/s were established to evaluate the fatigue life of tension insulator strings. The stress results revealed the at-risk parts in tension insulator strings and their failure modes. The fatigue life results showed 17.1 and 33.4 years for the GD (Guan Dian)-fittings and the upper U-shackles, respectively. This study can provide a useful guideline for optimization and safety evaluation of fittings. [ABSTRACT FROM AUTHOR]

This paper proposes a cloud-assisted joint charging scheduling and energy management framework for unmanned aerial vehicle (UAV) networks. For charging the UAVs those are extremely power hungry, charging towers are considered for plug-and-play charging during run-time operations. The charging towers should be cost-effective, thus it is equipped with photovoltaic power generation and energy storage systems functionalities. Furthermore, the towers should be cooperative for more cost-effectiveness by intelligent energy sharing. Based on the needs and setting, this paper proposes 1) charging scheduling between UAVs and towers and 2) cooperative energy managements among towers. For charging scheduling, the UAVs and towers should be scheduled for maximizing charging energy amounts and the scheduled pairs should determine charging energy allocation amounts. Here, two decisions are correlated, i.e., it is a non-convex problem. We re-formulate the non-convex to convex for guaranteeing optimal solutions. Lastly, the cooperative energy sharing among towers is designed and implemented with multi-agent deep reinforcement learning and then intelligent energy sharing can be realized. We can observe that the two methods are related and it should be managed, coordinated, and harmonized by a centralized orchestration manager under the consideration of fairness, energy-efficiency, and cost-effectiveness. Our data-intensive performance evaluation verifies that our proposed framework achieves desired performance. [ABSTRACT FROM AUTHOR]

Wind turbines (WTs) can beseriously damaged by lightning strikes and they can be struck by a significant number of flashes. This should be taken into account when the WT lightning protection system is designed. Moreover, WTs represent a path for the lightning current that can modify the well-known effects of the lightning discharge in terms of radiated electromagnetic fields, which are a source of damage and interference for nearby structures and systems. In this paper, a WT struck by a lightning discharge is analyzed with a full-wave modelling approach, taking into account the details of the WT and its interactions with the lightning channel. The effects of first and subsequent return strokes are analyzed as well as that of the rotation angle of the struck blade. Results show that the lightning current along the WT is mainly affected by the ground reflection and by the reflection between the struck blade and the channel. The computed electromagnetic fields show that, for subsequent return strokes, the presence of a WT almost doubles their magnitude with respect to a lightning striking the ground. Such enhancement is emphasized when the inclined struck blade is considered. [ABSTRACT FROM AUTHOR]

Domain-independent planning decouples a planning task specification from planning engines. As the specification is usually describing only the physics of the environment, actions and a goal, the planning engines being generic solvers designed to solve any planning task tend to struggle with tasks that can be easily solved by domain-specific algorithms. Additional control knowledge can, to large extent, bridge such a performance gap. Instead of providing a specific planner supporting a given form of control knowledge, control knowledge can be directly encoded within the planning task specification and thus can be exploited by generic planners. In this paper, we propose Attributed Transition-Based Domain Control Knowledge (ATB-DCK) that is represented by a finite state automaton with attributed states, referring to specific states of objects, connected by transitions imposing constraints on action applicability. ATB-DCK, roughly speaking, represents the “grammar” of solution plans that guides the search. We show that ATB-DCK can be compiled into a classical planning task and thus it complements domain-independent planning techniques. Using several domains from the International Planning Competitions as benchmarks, we demonstrate that this approach often considerably improves efficiency of existing state-of-the-art planning engines. [ABSTRACT FROM AUTHOR]

When lightning strikes a transmission line tower or shield wires, electromagnetic waves propagate through the tower back and forth, increasing the voltage across insulator strings. This can eventually lead to a back-flashover (BF), which may cause damage to equipment or costly power outages. To calculate the over-voltages and predict the probability of a BF, an accurate model of the tower and its grounding system is needed in electromagnetic transient (EMT) type simulators. There are a number of theoretical models for the equivalent circuit of a transmission tower. However, they either are not accurate enough or they are derived for a certain type of transmission tower, which limits their applicability. Numerical electromagnetic analyses have less simplifications compared to the theoretical solutions and are by far less expensive than field measurements. They also have the flexibility to analyse any type of tower. In this paper, the direct method for the measurement of tower impedance is implemented by NEC4 and applied to a 400-kV double circuit tower with all its details. The process of obtaining the wire network of the tower used in this paper is completely automated and it can be applied to any other type of transmission tower. The results of the numerical simulations are compared to those obtained with existing tower models. The developed model in this paper is capable of considering all the details of the tower and including the finite resistance of the ground and grounding electrodes. [ABSTRACT FROM AUTHOR]

Unmanned Aerial Vehicle (UAV) inspection has gradually replaced manual inspection of transmission tower, which produces many images. While it is laborious and time-consuming to manually analyze these images, there are also challenges in automatically detecting small-size defective components such as bolts in transmission tower images, due to problems including complex background, small size, and many similar objects of bolts. In this paper, by virtue of multi-scale features and context information, we propose a deep neural network named Camp-Net (Context Information and Multi-Scale Pyramid Network) to identify bolts defect in transmission tower images. First, multi-scale feature fusion combines deep features and shallow features in convolutional networks to detect small-size bolts. Second, context information fusion puts the information around bolts into the detection network to remove the disturbance of complex background and similar objects. An image dataset containing defective bolts and normal bolts is constructed for model training and testing. Experimental results show that bolts with loose pins and bolts without pins among fittings in transmission tower can be accurately identified with the proposed model. The Average Precision (AP) of defective bolts detection of this model can be 11.4% higher than that of the commonly used high performance model, Faster R-CNN. [ABSTRACT FROM AUTHOR]

This paper encompasses various topics for 5G-involved broadcasting under the common context converged distribution of 5G media. Particularly, two primary subtopics are addressed: An overlaid coexistence of 5G terrestrial broadcast and Advanced Television Systems Committee (ATSC) 3.0; and dual connectivity applications built on top of the convergence between digital broadcasting and 5G unicasting. In the first part, a viable, time-sharing co-transmission system is introduced to overlay 5G Broadcast and ATSC 3.0 frames in the same radio spectrum. The system is carefully designed to comply with current 5G and ATSC 3.0 standards, so that it does not require modifications in either ATSC 3.0 or 5G specifications. To help the future planning in a technical aspect, the reliability performance is in-depth compared between 5G Broadcast and ATSC 3.0 frames, and the motivation of tower overlaying is discussed as well. Subsequently in the $2^{\mathrm{ nd}}$ part, the convergence is in parallel explored with respect to the dual connectivity. To settle a broad-ranged consensus for future convergence, various possible use cases are proposed in an application aspect. Technical, conceptual proposals and implementations are presented, specifically related to edge caching; 8K streaming (with a working prototype); large-scale software updating; data security; and location tracking. We hereby point out how dual connectivity can contribute to realistic scenarios. In turn, the scope of convergence use cases is desirably expanded, so that would encourage the initiatives bridging 5G and broadcasting into practice. [ABSTRACT FROM AUTHOR]

The new characteristics and phenomena of hybrid AC/DC transmission grids challenge the conventional protection concepts. In hybrid AC/DC overhead line systems, AC and DC systems are located on the same support structure. As a result, electromagnetic and galvanic interactions between the AC- and the DC-line influence the AC-protection and the DC-control in a novel and complex way. This paper presents key findings and solutions from a current 400-kV-hybrid AC/DC overhead line project in Germany. The focus is on AC/DC intersystem faults, i.e. galvanic contact between DC and AC systems. Fault detection and fault response of the AC-protection and the DC-control as well as a proper AC/DC protection coordination are discussed. The paper illustrates the challenges of a secure and dependable fault clearing and indicates solution methods. The findings of this paper are based on EMT simulations with detailed PSCAD-models of the hybrid AC/DC overhead line and the VSC-converters. Laboratory protection tests have been conducted and confirmed the results. [ABSTRACT FROM AUTHOR]

Systematic deployment of digital fault recorders has made considerable amounts of field data available and raised the interest to compute fault resistance values from large sets of power system faults and analyze the results statistically. Published results are valuable, however scarce. The present paper gives further contributions by showing results obtained from 89 fault records, for the 400 kV, 220 kV, and 150 kV voltage levels, comparing these with recently published data. Furthermore, the present paper addresses the fundamental question on the existence of a theoretical distribution capable to describe the fault resistance value. For such purpose, an exploratory data analysis is applied to the new results, and a comparison between the exponential and the Weibull distribution is carried out. Results show that both distributions can describe the field data based distributions, the Weibull being more adequate for low resistance values. [ABSTRACT FROM AUTHOR]

Task allocation is a critical phase of project management. Tree-type structures are frequently used constraints to obtain a pertinent task allocation. They can illustrate where one task may require numerous agents and when an agent can be assigned to different tasks (roles). The process of task allocation is made more complex when administrators need to satisfy sequential and fixed branch relationships between/among tasks (roles). This paper formalizes the tree-structured task allocation problem (TSTAP) with group multirole assignment (GMRA) and proves necessary conditions, the necessary and sufficient condition, as well as sufficient conditions, of TSTAP. The formalization makes it easy to find a solution with the IBM ILOG CPLEX optimization package (CPLEX). The necessary conditions improve the CPLEX solution by eliminating infeasible cases. The necessary and sufficient condition describes the solution space of TSTAP completely. Another exciting result is that the sufficient conditions can not only improve the CPLEX solution by describing a practical approximate solution space but also help decision-makers and human resource officers organize a team in order to successfully assign tasks. The proposed approach is verified by simulation experiments with respect to a real-world problem. The experimental results present the practicability of the proposed solutions in this paper. This paper was motivated by general cooperative projects whose tasks have tree-structured relationships. This can make the problem of successful multitask assignment extremely challenging. The traditional method of assignment such as the KM algorithm can no longer solve this problem. To solve the assignment problem with tree-structured relationships, an efficient many-to-many assignment with constraints is required. The proposed approach provides theoretical and technical foundations for efficient assignment of TSTA, which can not only provide a viable and effective assignment scheme for TSTA problems but also help human resource officers to formulate reasonable plans according to the relationships between/among tasks. [ABSTRACT FROM AUTHOR]

The impulse grounding performance of distribution lines tower is the key factor to lightning protection. Few field high-current impulse test researches are conducted on distribution line tower. In this paper, we used a mobile high-current impulse generator to conduct test on a 10 kV distribution line tower. The peak value of the current injection is 6 kA to 16 kA. The impulse impedance and the surface potential distribution are measured and analyzed. Based on the CDEGS software, an equivalent modeling of the experiment was carried out. The influence of soil ionization was taken into account by the method of changing the conductor radius through two rounds of calculation. The simulation and measured results were basically consistent. Experiments have shown that the soil ionization effect has an important impact on lightning performance of distribution line tower. The graphite earthing modules (GEMs) and pulling wires can significantly reduce the impulse impedance of the tower. The potential rise of the earth surface at a distance of 30 m from the tower can reach 1 kV at peak, under an injection of 7.15 kA. [ABSTRACT FROM AUTHOR]

Vegetation encroaching on overhead power lines can cause short circuit faults and pose a major threat to the security and stability of power grids. Therefore, establishing an effective visual detection algorithm to oversee potential circuit failures of the power lines is critical to the ongoing inspection of vegetation encroachment. This paper establishes a deep learning-based detection framework that utilizes the images obtained from vision sensors mounted on power transmission towers. The proposed detection framework includes three cascaded modules: (1) detection of vegetation regions based on the Faster Region Convolution Neural Network (Faster R-CNN), (2) detection of power lines based on the Hough transform, and (3) detection of vegetation encroachment based on an advanced stereovision (SV) algorithm. In particular, the proposed SV algorithm converts the detected two-dimensional (2D) image data of the vegetation and power lines to three-dimensional (3D) height and location results in order to obtain precise geographical locations. Case studies using field captured images provided by a Transmission System Operator (TSO) demonstrate the effectiveness of the proposed framework in detecting vegetation failures, thus improving overall reliability and reducing economic loss. [ABSTRACT FROM AUTHOR]

High-frequency overvoltages are most dangerous for the insulation of transformer coils. It is because high-frequency pulse voltage creates an uneven distribution of voltage across the windings. The coil's first turns receive a disproportionately high voltage drop, leading to the inter-turn circuit. The paper analyzes the types of lightning pulses and proposes a new suppression method based on the anomalous skin effect in a multilayer material and the design in the form of a coil. The developed device is simulated, and the results of overvoltage monitoring at the substation with the installed high-frequency overvoltage suppression device are analyzed. [ABSTRACT FROM AUTHOR]

The paper presents an industry-validated technique for analysing the technical state of overhead power transmission lines and forecasting their residual life with the ability to predict their repairs and maintenance schedule. The authors propose a new approach to overhead lines technical state identification based on the analysis of its components: towers, conductors and insulation nodes. Also, within the study, an indirect method for assessing the wear indicator of overhead power transmission lines has been developed, taking into account the previously carried out replacement of its elements and components. The feasibility of extending the life of the overhead power transmission line components based on residual life assessment methods is justified. The developed methodology is intended to energy utilities as well as to engineering supervision organisations performing overhead power transmission lines surveys. Novel recommendations are formulated to assess the overhead transmission lines wear. [ABSTRACT FROM AUTHOR]

This paper describes systems, devices, and methods to implement a bi-directional integrated inter-tower wireless communications network (IITWCN). The described technology can be implemented in combination with the Broadcast Core Network (BCN) in next generation broadcast eco-system and, therefore, support new business cases for broadcast operators such as the delivery of flexible datacasting services or support broadcast or point-to-point Internet services. The introduced bi-directional inter-tower communications network (ITCN) extends the previous unidirectional in-band distribution links (IDL) and adopts the on-channel repeater (OCR) as a simplified backhaul solution in single frequency networks (SFN). The concept of the coordinated ITCN is also presented, aiming at future broadcast Internet services. The ITCN provides a scalable and configurable network solution embedded in a broadcast system, which becomes independent from any non-broadcasting telecommunication infrastructure. The described technology partially relies on the infrastructure of the underlying broadcast/multicast network, using the allocated service channels without requiring additional frequency bands or a separate frequency band. The bi-directional inter-transmitter communication links are therefore referred to as integrated transmission links and the corresponding network as an integrated network. [ABSTRACT FROM AUTHOR]

An electric potential appears at floating wires located within a strong electric field. This phenomenon can be used to supply small isolated communities situated close to Extra-High Voltage transmission lines. This non-conventional distributed generation system has been studied for the last years. However, to improve the power generation system the optimal position of the floating wires, number of wires used, bundle radius, and type of wires must be properly identified. This paper presents a mathematical model solved with genetic algorithm to design a collector system with optimized induced voltage and minimized project cost, identifying the optimal reactor used for voltage regulation. The algorithm was applied to design a collector system that can tap-off 100 kW from a 230 kV transmission line. The trade-off between objectives and the Pareto optimal solutions were evidenced via several simulations using the weighting sum approach. These results allowed to identify a final geometry according to a-posteriori designer preferences. [ABSTRACT FROM AUTHOR]

Overhead lines are important parts of distribution networks at present. Assessment and prediction of their health status is of great significance to ensure the reliable operation of distribution network. This paper presents a method for assessing and predicting the health status of overhead lines based on health index (HI). First, the key features set of overhead lines including ontological and nonontological factors is determined. Then, a calculation method for evaluating HI based on analytic hierarchy process and technique for order preference by similarity to an ideal solution is proposed. Subsequently, the health assessment results of the actual 110 and 10 kV overhead lines located in China show that the proposed method could reflect the actual situation of overhead lines well. Finally, based on the proposed method, this paper takes two areas of China, Beijing and Nanjing, which have different climatic conditions, as research objects, and studies the influence of natural factors on the health status of overhead lines, respectively. Based on the analysis results, the health statuses of the overhead lines in the two regions are predicted. The research results of this paper can provide guidance for the operation and maintenance of overhead lines. [ABSTRACT FROM AUTHOR]

Noncontact monitoring technique of mechanical and electrical states is increasingly attractive for the overhead transmission system. This paper proposes a new technique to detect the tower inclination and transmission line sag, and measure transmission current simultaneously. The key of this technique is to use the ground magnetoresistive (MR) sensor to measure the magnetic flux density along the center line from the three-phase transmission lines. Moreover, the magnetic field (MF) calculation formulas for a tilted tower are given in this paper. Finally, with MF calculation formulas, an algorithm based on artificial immune system (AIS) is applied to estimate the transmission line sag and tower tilt angles, and reconstruct currents. Model simulations of an overhead transmission system are carried out to verify the idea. The simulation results validate the feasibility of this noncontact approach to estimate mechanical parameters and reconstruct electrical parameters for overhead transmission system. [ABSTRACT FROM AUTHOR]

A tower crane is a nonlinear mechatronic system with complicated underactuated characteristics, which is widely used in modern construction sites. At present, most existing methods for tower cranes are proposed by linearizing the original nonlinear dynamics near equilibrium points, which are, thus, prone to suffering from unexpected steady errors due to such factors as unmodeled dynamics, imperfect friction compensation, etc., since they have not included integral terms in either controller design or stability analysis. Therefore, in this paper, an improved feedback controller with an elaborately constructed integral term is proposed for 3-D tower cranes without linearization, which can achieve both antiswing and positioning control while being able to effectively reduce steady errors in the presence of, e.g., inaccurate friction compensation. Furthermore, asymptotic stability results are proven through rigorous theoretical analysis. Owing to no linearization, the proposed controller is applicable when state variables (e.g., cargo swing angles) are not close enough to the equilibrium points, which makes it suitable for complicated working conditions. Hardware experimental results are included to verify the effectiveness of the proposed controller. Note to Practitioners—This paper is motivated by the requirement of effective control methods for tower cranes. Tower cranes are widely applied in modern construction sites to fulfill cargo transportation tasks. For such systems, the jib slew motion not only enlarges the workspace but also brings more difficulties to suppress unexpected cargo swing during the transportation process. Up until now, most existing methods use simplified system models or need exact model knowledge, which are difficult to reflect real dynamics in many practical situations. To handle these existing problems, in this paper, a novel feedback control approach embedded with an elaborately constructed integral term is presented without model linearization. By introducing the integral term, even when frictions are inaccurately compensated, steady errors can be reduced effectively and, hence, the positioning accuracy can be improved. Also, the proposed controller can handle parametric uncertainties. By applying the proposed controller, the closed-loop system achieves asymptotic results, which is rigorously proven theoretically. Finally, the effectiveness of the proposed controller is verified by implementing several groups of hardware experiments. In the future studies, we will apply the proposed method in practical applications. [ABSTRACT FROM AUTHOR]

We propose, in this paper, an observer-based nonlinear feedback controller for four degrees of freedom (4-DOF) offshore ship-mounted tower cranes, which includes a robust-type term to address the observation uncertainty, and a switching logic tuning mechanism to update the involved unknown parameter. As a typical nonlinear underactuated mechatronic system, unlike the land-fixed tower cranes, an offshore ship-mounted tower crane also suffers from persistent disturbances caused by sea waves or currents, which leads to many difficulties and challenges in the controller design of such systems. Existing offshore crane control methods require either linearizations or approximations when performing analysis; moreover, most of them are only applicable for simplified 2-DOF crane models, and the ranges of system state errors cannot be guaranteed during the overall process. Motivated by these facts, to achieve simultaneous accurate jib/trolley positioning and fast payload swings suppression against complex unknown external disturbances, in particular, a disturbance observer is first designed in this paper, based on which a novel nonlinear switching logic-based control scheme for offshore cranes with jib rotation and horizontal transportation is proposed. As far as we know, the proposed method yields the first observer-based feedback closed-loop control without simplification operations to the original 4-DOF offshore tower crane dynamics and achieves the first asymptotic stability of the closed-loop system’s equilibrium point for offshore cranes. To support the theoretical derivation, the corresponding stability analysis of the closed-loop system’s equilibrium point is implemented by Lyapunov techniques. Numerous simulation and hardware experimental results are presented to demonstrate the superior performance of the proposed method. Note to Practitioners—This paper is motivated by the issue of controlling a four- degree-of-freedom (4-DOF) offshore ship-mounted tower crane system under the effects of unknown external disturbances. In practical applications, the persistent disturbances caused by sea waves or currents can always happen and make the offshore crane operation very challenging. Moreover, it brings more difficulties in the controller design for such a system due to its nonlinear underactuated property. Existing control approaches for offshore cranes are developed based upon linearized or oversimplified crane models or require exact model knowledge, and they may not work well in the presence of harsh sea conditions. Toward this end, this paper suggests a new control approach for 4-DOF offshore tower cranes suffering from sea wave effects to achieve a satisfactory performance. The asymptotic stability of the closed-loop system’s equilibrium point is derived, implying that the accurate jib/trolley positioning and fast payload swings suppression against complex unknown external disturbances are achieved simultaneously. Preliminary physical experiments implemented on a self-built offshore tower crane hardware test bed verify the effectiveness and the robustness of the proposed observer-based control method. In the future research, we will apply the suggested control approach to industrial offshore crane systems to improve their working efficiency. [ABSTRACT FROM AUTHOR]

Modeling of lightning return-stroke channel affects significantly the estimation of fast-front overvoltages arising across overhead line insulators, thus, also the lightning performance of power lines. This paper introduces a simplified method for estimating the minimum lightning currents causing shielding failure flashover and backflashover of overhead transmission line insulation, as affected by lightning channel equivalent impedance. The validity of the proposed methodology is demonstrated through ATP-EMTP simulations of typical 66 up to 765-kV overhead transmission lines with variable tower ground resistance. An assessment is made of the effects of lightning channel equivalent impedance on the lightning performance of overhead lines, that is, shielding failure flashover and backflashover rates. Lightning channel equivalent impedance values of 1000 and 400 Ω are suggested, respectively, for shielding failure and backflashover studies, based on the results obtained in this paper together with a discussion on the literature data regarding channel impedance. [ABSTRACT FROM AUTHOR]

Wind turbine generators in a windfarm are connected by underground cables. Lightning sometimes strikes a nacelle or a blade. Lightning overvoltages due to a direct lightning strike to the system cause damages in the underground cable. Many parameters should be investigated to establish a rational lightning protection design for wind power generation system. Numerical simulation is a useful method to discuss the influence of the parameters on the lightning overvoltages. This paper uses an Electro-Magnetic Transients Program for the lightning surge analysis. This paper discusses the influence of grounding method of metallic sheath of the cable and grounding resistance on the lightning overvoltages for the direct lightning strike to the generation system. [ABSTRACT FROM AUTHOR]

In microcellular communications, the transmitting antennas can be installed at low heights above the ground. However, even for low elevation towers, installation cost is still high. One of the possible ways for the deployment of base station antennas is to install them near the ground in order to do away with the tower. The main purpose of this paper is to suggest installation of the radiating antennas near the ground and tilting their orientation toward the sky—a totally nonintuitive solution. It will be shown that such deployments have the potential of reducing slow fading and can further enhance the signal strength close to the radiating antenna. This paper provides measured data for the received fields to validate the theoretical conjecture of such a deployment in various environments. The measured results are presented for 245, 800, 1000, and 2400 MHz. It is illustrated that such an unorthodox deployment can result in a low cost for the installation of base station antenna as the towers are not necessary. This can be useful in restoring communications in emergency situations where minimum infrastructure exists. [ABSTRACT FROM AUTHOR]

This paper explores tower field constructions and hardware optimizations for the WG-16 stream cipher. The constructions ${\mathbb {F}}_{(((2^2)^2)^2)^2}$ and ${\mathbb {F}}_{(2^{4})^4}$ were chosen because their small subfields enable high speed arithmetic implementations and their regularity provides flexibility in pipeline granularity. A design methodology is presented where the tower field constructions guide how to proceed systematically from algebraic optimizations, through initial hardware implementation, selection of submodules, pipelining, and finally detailed hardware optimizations to increase clock speed. The highest frequency WG(16, 32) keystream generator, obtained for the 65 nm ASIC library, reached a clock speed of 2.44 GHz at 26.3 kGE, and the smallest area keystream generator achieved a clock speed of 0.33 GHz at 9.9 kGE. The highest frequency FPGA implementation on a Xilinx Spartan 6 reached a clock speed of 256 MHz using 631 slices. In addition, the paper demonstrates that LFSR feedback polynomials can be optimized to increase security without hurting performance, and retiming optimizations can be used to increase clock speed without increasing area. [ABSTRACT FROM AUTHOR]

In high-voltage direct current (HVDC) transmission systems comprising overhead line (OHL) sections as well as cable sections, the dc cable system is exposed indirectly to lightning strokes. In case of HVDC cable systems with extruded insulation the present test recommendations do not specify lightning impulse test levels related to rated system voltage. Instead, preliminary electromagnetic transient studies are required to determine the absolute maximum lightning impulse voltage the cable might experience. Within this paper, the general lightning behavior of OHL-cable mixed systems subsequent to the occurrence of a backflashover as well as a shielding failure is investigated for a 525 kV HVDC transmission scheme. This paper presents a modeling method to calculate occurring lightning overvoltages along a dc cable embedded between OHL sections. Based on a detailed parametric study using time-domain simulation, maximum lightning impulse voltages along the cable system are determined, and evaluated with regard to impulse level and polarity. The impact of project related parameter such as cable length, tower design, and tower grounding conditions on lightning overvoltage affecting the cable is demonstrated. [ABSTRACT FROM AUTHOR]

Voltage and current waveforms of transmission lines struck by lightning are calculated for use in back flashover analysis. Calculation by using equivalent circuits is the general practice, however, there are limited experimental results for reference to evaluate validity of developed equivalent circuits under various line conditions. Calculation results by numerical electromagnetic analysis can be used as references if they are proved reliable. In this paper, the voltage rises at a model of a 154 kV transmission line hit by lightning is calculated by Method of Moments (MoM) and FDTD for comparison. They solve Maxwell's equations by using different algorithms, so, if the calculated results by these methods reasonably agree under various line conditions, the results of these numerical analyses are regarded reliable. The calculated voltage and current waveforms by the two numerical methods agree well under a variety of footing resistance of transmission towers, thus the authors conclude that the calculated results by FDTD or MoM can be employed as references to evaluate validity of circuit models for back flashover analyses. Thus, the results calculated by circuit analysis are compared with those calculated by FDTD. The multistory tower model (Ishii model) better reproduces the voltage waveforms in a wide range of the footing resistance than simple circuit models of a tower, and can be easily tuned for further accuracy. [ABSTRACT FROM AUTHOR]

The implementation of AES S-boxes is one of the most extensively studied areas of cryptography. In this paper, we propose three new hardware designs for the AES S-box that can serve in the forward, inverse and combined data paths. Each of these designs represents the smallest AES S-box ever proposed in its respective category. We achieve this goal by using new tower field representation over normal bases and optimizing each and every block inside the three proposed architectures. Our complexity analysis and ASIC synthesis results in the CMOS STM 65 nm, as well as the NanGate 15 nm technologies, show that our designs outperform their counterparts in terms of area and power. [ABSTRACT FROM AUTHOR]

In secure cryptographic primitives, such as block ciphers, the reliability of hardware implementations needs to be closely considered because faults in the hardware implementations can potentially reduce or impact on the underlying security. In this paper, we present approaches to detect errors in hardware implementations of the inversion in GF(28). The proposed approaches are based on both nonredundant and redundant arithmetic, utilizing normal basis (nonredundant) and two redundant Galois field representations, i.e., polynomial ring representation and redundantly represented basis through tower fields. To the best of our knowledge, this is the first work focusing on the error detection architectures for redundant arithmetic-based inversion in GF(28). The presented signature-based schemes in this paper are general and can be applied to block ciphers with 8-bit S-boxes, such as Camellia, SMS4, the advanced encryption standard, and CLEFIA. We present the results of error simulations and application-specific integrated circuit implementations to demonstrate the utility of the presented schemes. Based on the specific implementation’s security/reliability objectives and the overhead/degradation tolerance for implementation/performance metrics, one can fine-tune and tailor the proposed work to achieve more reliable inversions in GF(28). [ABSTRACT FROM PUBLISHER]

The paper reports on a second part of the lightning performance study that was conducted on overhead double-circuit lines 170 kV operated by Israel Electric Corporation (IECo). The first part of this study was published this year in TPWRD vol. 31 No. 2 ([1]) which introduces the local environmental data including a long-term lightning incidence records, tower footing resistance, and route terrain characteristics. The goal of the present paper is to demonstrate application of the data-inputs from [1] to analysis of the relationship between the line failure rate and its design and environmental parameters. The findings imply that the prevalent lightning failure mechanism in IECo Grid is direct-strike related. The acquired results prove a conclusion on that the ineffective shielding design in combination with local stroke current statistics, route topography, and long spans may seriously compromise line reliability, even with temperate local lightning activity. Disregarding the route terrain specificity may falsify the shielding flashover failure rate assessment and devaluate the line protection design. [ABSTRACT FROM AUTHOR]

This paper deal with the electrical performance of a newly proposed fully composite pylon in Denmark, which has a unibody composite cross-arm at 420 kV highest system voltage level. Electric field consideration along the insulations of the novel unibody cross-arm is one of the most important requirements in the design process of a non-traditional pylon. In this paper, ANSYS finite element software is used to calculate the electric field and potential distribution around and inside the fully composite pylon. Electric field criteria related to the design of composite cross-arms are reviewed and applied for interpreting the electrical performance of the unibody cross-arm at power frequency stresses. Three different designs of non-conductive conductor clamp are assumed for the attachment points between phase conductors and the unibody cross-arm. The side effects of conductor clamp are included in 2D modeling in order to determine the minimum required height for phase conductors at the top of the unibody cross-arm. Considering the side effects of phase conductors at both sides of conductor clamp, the application of steel enclosures with an appropriate diameter is introduced to be used around the phase conductors in order to reduce the electric field magnitudes in the region of the conductor clamp. Finally, the feasibility of utilizing steel enclosures for modifying electric stresses inside the conductor clamp and unibody cross-arm is investigated by a 3D finite element analysis. [ABSTRACT FROM AUTHOR]

This paper presents the modeling and characterization of the tower shadow effects using a wind turbine emulator in a laboratory environment. In particular, the downwind wind turbines are considered here as their tower shadow effects are more significant compared to the upwind counterpart. Simulation and experimental results have shown that the wind speed deficit due to this nonideal effect is significant. In addition, the tower shadow effects occur typically two to three times per revolution, depending on the number of blades. The modeling of the tower shadow profiles for tubular and four-leg tower configurations is presented. Typically, these towers are used in small wind turbine applications. The tower shadow profiles are emulated experimentally using a wind turbine emulator with its characteristics being explained. The limitations of emulating the tower shadow effects using a wind turbine emulator are demonstrated through the frequency response test performed in this study. In this study, the wind turbine emulator is connected to an isolated grid which is formed by three single-phase inverters. Finally, this paper concludes with a sensitivity analysis of the power oscillations for different widths and magnitudes of the tower shadow profile. [ABSTRACT FROM PUBLISHER]

The electromagnetic fields, which are produced by lightning currents flowing into a transmission tower and into overhead ground wires, spherically expand with time, and propagate as non-transverse electromagnetic (TEM) waves at least within the round trip time of the traveling wave along the tower. In this paper, a distributed-parameter line model of a vertical double-circuit transmission tower with an overhead line struck by lightning is composed considering the non-TEM characteristics. The surge impedances of the tower, ground wires, and phase conductors increase with time and reach their TEM-mode or steady state values with time constants determined from the configuration. In addition, the significant wave attenuation along the tower is included in the circuit model according to the propagation characteristic determined by the tower configuration. The virtual inductive grounding impedance or damping circuits for approximately representing the wave attenuation is no longer needed. The proposed model is applied to four types of transmission towers. Waveforms of voltages across insulator strings computed by the finite-difference time-domain method, which are regarded as the reference, are well reproduced by the proposed model. Computation efficiency is drastically improved by the proposed model comparing to the numerical electromagnetic field analysis. [ABSTRACT FROM AUTHOR]

Locally repairable codes have been investigated extensively in recent years due to practical applications in distributed and cloud storage systems. However, there are few asymptotic constructions of locally repairable codes in the literature. In this paper, we provide a new explicit asymptotic construction of locally repairable codes over arbitrary finite fields from local expansions of functions at a rational place. This construction gives a Tsfasman-Vladut-Zink type bound for locally repairable codes. Its main advantage is that there are no constraints on both locality and alphabet size. Furthermore, we show that the Gilbert-Varshamov type bound of locally repairable codes over non-prime finite fields can be improved for sufficiently large alphabet sizes. [ABSTRACT FROM AUTHOR]

This paper presents a method for the development of galloping distribution maps. The number of galloping days and return period are utilized to deal with the problems of lack of operational experiences for those area without transmission lines, and let the proposed maps be suitable for transmission lines with different voltages. By employing the proposed method, the galloping distribution map can estimate the galloping probability of overhead transmission lines in a more reasonable and accurate manner. [ABSTRACT FROM AUTHOR]

Lightning peak current is one of the most important parameter concerning the studies of the lightning phenomena. Nowadays, with a continuous dissemination of elevated structures, such as telecommunication towers, the study of the lightning peak current could be intensified with the installation of measurement devices in large scale. Thus, it is useful to develop a device that is robust, compact, low cost, and allows data collection. This paper describes a high-current sensor operating in a range up to 100- and 7.7-kA resolution. The system consists of a self-integrating Rogowski coil connected to the electret sensor by a coaxial cable. The electret sensor is installed in a sturdy and inexpensive casing at the tower base. Measurements indicate a linear and precise correlation between the voltage generated by the coil, installed on the top of the tower, and the impulse current from lightning. [ABSTRACT FROM AUTHOR]

Noninvasive contactless methods for electric power line monitoring based on magnetic field measurement have become an interesting topic for researchers and the electric power industry since introduction of the Smart Grid concept. By measuring and analyzing magnetic field originating from currents in power line conductors, it is possible to detect faults in the network. In medium voltage distribution networks, where a variety of different pole geometries are present, different criteria for fault detection have to be employed for each geometry, which complicates detection and influences accuracy. This paper proposes a novel approach for fault detection in medium voltage distribution networks which is based on processing of signals measured by low cost contactless magnetic field sensors. In order to create a generalized method for fault detection, a sequence of mathematical transformations of the measured magnetic field components is applied. A novel geometric transformation which eliminates influence of pole geometry is introduced, providing signals from which steady-state symmetrical components of the rotating magnetic field are computed. Those components are used as general fault detection criteria. The proposed approach is confirmed to be applicable for different fault types by a set of experiments on three-phase overhead power line model scaled to laboratory conditions. [ABSTRACT FROM AUTHOR]

Over the last years, extreme weather events have caused extensive damages in power systems, leaving millions of customers without electricity and therefore highlighting the necessity to enhance power system resilience. This paper proposes a resilience constrained day-ahead unit commitment framework for increasing resiliency of a power system exposed to an extreme weather event. The weather-dependent failure probabilities of the transmission lines are taken into account in order to decide the scheduling of generators that minimizes load shedding in the most efficient way, while respecting operating limits of the system. The problem is formulated as a tri-level optimization problem that is transformed to a bi-level problem using duality theory and linearization techniques. The problem is solved as a two-stage robust optimization problem using a Column & Constraint Generation based decomposition algorithm. The master problem provides the unit commitment and the subproblem identifies the worst damage scenario due to weather event. A Sequential Monte Carlo simulation of a modified IEEE Reliability Test System and IEEE 118-bus System is applied to illustrate and validate the effectiveness of the proposed framework. [ABSTRACT FROM AUTHOR]

In this paper, we present current pulses from upward lightning, which have been measured since 2011 at the new top structure of the Peissenberg Tower, Germany. The study comprises 38 negative and two positive flashes, which contained 199 current pulses. About 49 of them were return stroke current pulses, 133 of them were current pulses, which superimposed the initial continuous current (ICC-pulses), and 17 of them were M-component current pulses, which superimposed the continuing current of a preceding return stroke. The current pulses are used to evaluate the performance of the European lightning location system EUCLID. Fifty one (25.6%) out of the 199 current pulses were detected by EUCLID, 40 (81.6%) return stroke current pulses, and 11 (8.5%) ICC-pulses or M-component current pulses. The peak currents ranged from 0.1 to 40.8 kA. Two groups of current pulses could be identified. The first group is related to branches of nearby downward lightning which got in contact with the tower. Therefore, EUCLID reported much higher peak currents (more than 100%) compared to the peak currents measured at the Peissenberg Tower. The first group comprises the total of nine current pulses (six ICC-pulses, three return stroke current pulses). The second group of current pulses is related to upward lightning initiated from the top of the tower. The peak current inferred from EUCLID deviates much less from peak current measured at the Peissenberg Tower. The peak current was overestimated by about 20% by EUCLID. The second group comprises the total of 42 current pulses (4 ICC-pulses, 1 M-component current pulses, and 37 return stroke current pulses). The peak currents ranged from 3.1 to 40.8 kA, the geometric mean (GM) was 9.4 kA. About 30% of these events were misclassified as intra-cloud pulses by EUCLID. The GM of the location error was 161 m for all events, and 132 m considering only the return stroke current pulses. [ABSTRACT FROM AUTHOR]

Current crowd density estimation technologies that leverage IR depth perception, video and image processing or WiFi/BLE-based sniffing and probing have privacy and deployment issues. This paper presents a novel method for non-intrusive crowd density estimation that monitors variation in EM radiation within an environment. The human body's electrical and magnetic characteristics can be correlated with variations in available EM energy. This allows for the determination of the number of people within a room. Simulations conducted using Comsol to analyse and measure electromagnetic energy levels inside a room containing human bodies. Experimental analysis provides validation of the simulation results by showing $\text{0.8}\;\text{dBm}$ drop on the average level of EM energy per person. [ABSTRACT FROM AUTHOR]

Reed-Muller codes are among the most important classes of locally correctable codes. Currently local decoding of Reed-Muller codes is based on decoding on lines or quadratic curves to recover one single coordinate. To recover multiple coordinates simultaneously, the naive way is to repeat the local decoding for recovery of a single coordinate. This decoding algorithm might be more expensive, i.e., require higher query complexity. In this paper, we focus on Reed-Muller codes with usual parameter regime, namely, the total degree of evaluation polynomials is $d=\Theta ({q})$ , where $q$ is the code alphabet size (in fact, $d$ can be as big as $q/4$ in our setting). By introducing a novel variation of codex, i.e., interleaved codex (the concept of codex has been used for arithmetic secret sharing), we are able to locally recover arbitrarily large number $k$ of coordinates of a Reed-Muller code simultaneously with error probability $\exp (-\Omega (k))$ at the cost of querying merely $O(q^{2}k)$ coordinates. It turns out that our local decoding of Reed-Muller codes shows (perhaps surprisingly) that accessing $k$ locations is in fact cheaper than repeating the procedure for accessing a single location for $k$ times. Precisely speaking, to get the same success probability by repeating the local decoding algorithm of a single coordinate, one has to query $\Omega (qk^{2})$ coordinates. Thus, the query complexity of our local decoding is smaller for $k=\Omega (q)$. If we impose the same query complexity constraint on both algorithm, our local decoding algorithm yields smaller error probability when $k=\Omega (q^{q})$. In addition, our local decoding is efficient, i.e., the decoding complexity is ${\mathrm{ Poly}}(k,q)$. Construction of an interleaved codex is based on concatenation of a codex with a multiplication friendly pair, while the main tool to realize codex is based on algebraic function fields (or more precisely, algebraic geometry codes). [ABSTRACT FROM AUTHOR]

Locally repairable codes have been investigated extensively in recent years due to practical applications in distributed storage as well as theoretical interest. However, not much work on asymptotical behavior of locally repairable codes has been done until now. In particular, there is little result on constructive lower bound of asymptotical behavior of locally repairable codes. In this paper, we extend the construction given by Barg et al. via automorphism groups of function field towers. The main advantage of our construction is to allow more flexibility of locality. Furthermore, we show that the Gilbert–Varshamov type bound on locally repairable codes can be improved for all sufficiently large alphabet size $q$. [ABSTRACT FROM AUTHOR]

Emerging visual-based driving assistance systems involve time-critical and data-intensive computational tasks, such as real-time object recognition and scene understanding. Due to the constraints on space and power capacity, it is not feasible to install extra computing devices on all the vehicles. To solve this problem, different scenarios of vehicular fog computing have been proposed, where computational tasks generated by vehicles can be sent to and processed at fog nodes located for example at 5G cell towers or moving buses. In this paper, we propose Chameleon, a novel solution for task offloading for visual-based assisted driving. Chameleon takes into account the spatiotemporal variation in service demand and supply, and provides latency and resolution aware task offloading strategies based on partially observable Markov decision process (POMDP). To evaluate the effectiveness of Chameleon, we simulate the availability of vehicular fog nodes at different times of day based on the bus trajectories collected in Helsinki, and use the real-world performance measurements of visual data transmission and processing. Compared with adaptive and random task offloading strategies, the POMDP-based offloading strategies provided by Chameleon shortens the average service latency of task offloading by up to 65% while increasing the average resolution level of processed images by up to 83%. [ABSTRACT FROM AUTHOR]

In a standalone hybrid wind-diesel-battery system, the battery lifetime is often optimistically over-predicted by hybrid system designers and battery manufacturers. As a result, battery replacement takes place more often than required. One of the reasons is due to the underestimation of battery wear from the short charge–discharge cycles, otherwise known as microcycles. A microcycle takes place when the power generation closely matches the load demand. The detrimental effect of microcycles on a battery-based standalone hybrid renewable energy system was previously investigated, however, only from the perspective of short-term renewable energy fluctuations. This research paper provides a new insight on the battery lifetime reduction, resulting from microcycles that are generated through the tower shadow phenomena. Downwind wind turbines are considered here, as their tower shadow effects are more significant compared to the upwind counterpart. This paper briefly presents the modeling of tower shadow profiles for both tubular and four-leg tower configurations. Experimental results have shown that the microcycles due to this nonideal effect are significant in a battery-based standalone hybrid system. The quantification of the battery lifetime reduction due to this effect is demonstrated. Finally, the paper concludes with a sensitivity analysis of the battery lifetime reduction for different tower configurations, operating at different load conditions. [ABSTRACT FROM PUBLISHER]

As the key equipment of ultra-high-voltage direct-current (UHVDC) transmission systems, the converter valve would bear different forms of overvoltage. Consequently, a wideband model for the $\pm $1100 kV UHVDC converter valve is essential for the converter system to make overvoltage analysis, insulation design, and electromagnetic disturbance prediction. This paper proposed a wideband modeling method for the $\pm $1100 kV converter valve. First, the physics-based wideband model for the key component in the converter valve module is built, of which the parameters could be obtained through genetic algorithm. Second, the parasitic capacitances are obtained through a simplified boundary-element method according to the given structure of the $\pm $1100 kV converter valve. By combining wideband models for key components in the converter valve module and the parasitic capacitances of the valve tower, the integrated wideband model for the converter valve could be obtained. The systematic modelling method proposed in this paper could also be of reference value to the modelling of other large-scale complex high-voltage power-electronic equipment. Finally, the experiments for converter valve module and converter tower are carried out, and the corresponding results justified the effectiveness and correctness of the proposed wideband model for the converter valve tower. [ABSTRACT FROM PUBLISHER]