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The Optimal Power Shutoff (OPS) problem is an optimization problem that makes power line de-energization decisions in order to reduce the risk of igniting a wildfire, while minimizing the load shed of customers. This problem, with DC linear power flow equations, has been used in many studies in recent years. However, using linear approximations for power flow when making decisions on the network topology is known to cause challenges with AC feasibility of the resulting network, as studied in the related contexts of optimal transmission switching or grid restoration planning. This paper explores the accuracy of the DC OPS formulation and the ability to recover an AC-feasible power flow solution after de-energization decisions are made. We also extend the OPS problem to include variants with the AC, Second-Order-Cone, and Network-Flow power flow equations, and compare them to the DC approximation with respect to solution quality and time. The results highlight that the DC approximation overestimates the amount of load that can be served, leading to poor de-energization decisions. The AC and SOC-based formulations are better, but prohibitively slow to solve for even modestly sized networks thus demonstrating the need for new solution methods with better trade-offs between computational time and solution quality. • This paper considers a planning problem for optimizating Public Safety Power Shutoffs. • The problem is modeled with 4 power flow formulationsm: AC, DC, SOC, and NF. • These formulations demonstrate a tradeoff between solution quality (accurate estimates of load shed) and solution speed (orders of magnitude difference). • The formulations are made available in the open-source software package PowerModelsWildfire.jl. [ABSTRACT FROM AUTHOR]

• This paper presents a new modeling for analyzing transient grounding system behavior during a direct lightning strike. • The modeling that we propose makes it possible to treat even a complex grounding circuit like that encountered in wind farms where we have several interconnected groundings. • This modeling developed directly in the time domain considers the effect of frequency and ground ionization. • The modeling that we propose uses the transmission line equations with frequency dependence, the vector fitting technique and the Finite Difference Time Domain numerical method. • The modeling that we propose makes it possible to overcome the numerical disadvantages that may be encountered when implementing a full-wave electromagnetic formalism when the structure studied has large geometric dimensions, inhomogeneous and has open boundaries. This paper presents a new model for analyzing transient grounding system behavior during a direct lightning strike. The modeling that we propose allows us to consider a simple grounding conductor buried horizontally or vertically, a grounding grid, wind turbine grounding system and grounding circuits for wind farms while including the aerial parts (towers and blades). This modeling is developed directly in the time domain taking into account the frequency dependence of the impedance and admittance of the wired conductors and of the electrical parameters of the soil (ρ, ε) and also considering the ionization of the soil. This formalism is based on transmission line equations, rational approximation by vector fitting and the Finite Difference Time Domain numerical method. The proposed formalism is verified considering both simulations and experimental results from available published researches. The Ground Potential Rise GPR in the grounding circuits of wind farms are discussed during the first stroke and also during the subsequent stroke whose frequency range generates more propagation of electrical waves along conductors. This formalism makes it possible to contribute to all knowledge/research of grounding systems. [ABSTRACT FROM AUTHOR]

• Data on the corona characteristics of AC conductors (LGJ-300/40) during rainfall were obtained from tests in an artificial climate chamber. • It was found that the AC corona characteristics of conductors were mainly affected by the rainfall intensity rather than the rain conductivity. • Rainfall has a greater effect on the corona characteristics of conductors compared to dry conditions, but moderate rain is recommended as a reference for corona design of transmission lines. • Raindrops cause distortions in the electric field strength in the vicinity of the conductor, leading to vibration and rupture of the raindrops, and the critical rupture electric field decreases as the radius of the raindrops increases. How to reduce the effect of rainfall on the corona discharge of conductors is a problem that must be considered in the design and operation of transmission lines. This paper takes LGJ-300/40 conductor as the sample, and experimentally investigates the influence of rain conductivity and rainfall intensity on the corona characteristics of AC conductor in multi-functional artificial climate chamber, and analyzes the surface electric field strength distribution of rain-drenched conductor and the vibration and rupture of raindrops. The results show that changing the rain conductivity does not affect the corona characteristics of AC conductor. Compared with the dry environment, the corona inception voltage decreases by 36.94 %∼45.16 % with the increase of the rainfall intensity (from drizzle to rainstorm), and the corona loss and the audible noise increase. The corona loss and the applied voltage satisfy the power function for different rain conductivities (or rainfall intensities), the corona characteristics of the conductor change less in moderate rain and above. The critical rupture electric field strength of water droplets decreases with the increase of raindrop radius. The results of this paper have some reference significance for the selection and design of AC transmission lines. [ABSTRACT FROM AUTHOR]

• At present, there is no systematic analysis of the causes of overheating in the research on connection fittings for extra-high voltage direct current transmission lines both domestically and internationally. Only through simulation of overheating defects, the impact of overheating on transmission lines has been studied, and no systematic investigation plan for related defect problems has been proposed. • The model proposed in this paper can be used for analyzing problems related to ±800 kV extra-high voltage DC overhead transmission lines, as well as for ultra-high voltage DC overhead transmission lines such as ±500 kV, and has strong universality. • This paper propose a systesmatic troubleshooting plan for related defect issues, which has important reference and guidance significance for such line fault problems. This paper studies the overheating defect of an extension rod in a ± 800 kV extra-high voltage direct current overhead transmission line, and proposes various factors that affect the overheating of the extension rod. Establish an equivalent model of an extra high voltage DC transmission line based on equipotential point and line parameter analysis, and calculate the model parameters. The proposed model can also be applied to ultra-high voltage DC overhead transmission lines such as ± 500 kV, and has strong universality. Simulation experiments show that if the equivalent resistance value of the split wire side is reduced by 0.01Ω, the power loss on the extension tie rod can be increased to 380.951 W; if the equivalent resistance value of the jumper side is increased by 0.01Ω, the power loss on the extension tie rod can be increased to 273.41 W. Combined with theoretical analysis and simulation verification, it is concluded that the main factor affecting the overheating of the extension rod is the change in the resistance value on the jumper side caused by the increase in contact resistance. A systematic troubleshooting plan for related defect problems is proposed, which has important reference and guidance significance for such line fault problems. [ABSTRACT FROM AUTHOR]

• The proposed single-ended fault location framework fully considers the effect of partial coupling, without requiring measurements from the remote ends. • Within the proposed framework, two methods based on impedance line model and fully distributed line model are presented. • The effectiveness of the proposed methods is validated through many simulation analyses. The proposed methods demonstrate some robustness towards measurement noises and parameter errors. Accurate fault location technology can not only speed up fault search but also enhance the power supply reliability. This paper introduces a single-ended fault location framework for single line to ground faults, taking into account the effects of partially coupled lines. The proposed framework relies only on local measurements. Within the proposed framework, the two methods proposed in this paper are based on the impedance line model and the fully distributed parameter line model, respectively. The impedance model based fault location method does not require iteration and has no risk of divergence, while the method based on the fully distributed parameter model has higher accuracy. The estimated results of the impedance-based method can be used as the initial values of the solution of the distributed parameter model based method. The proposed methods are validated through a number of testing cases, encompassing various fault locations, resistances, and coupling ratios. [ABSTRACT FROM AUTHOR]

• Proposes an improved YOLOv5s model which combines the GIoU, Mish, and CBAM modules. • The improved algorithm can effectively detect different-size insulator defects under different environmental backgrounds. • The AP value in detecting insulator defects can be improved by 5 %. As one of the most important components on the transmission line, the insulator is prone to failure, which affects the safe operation of electrical power system. Hence, it is crucial to accurately detect the insulator defects for further maintenance in time. Recently, with the development of artificial intelligence and target detection algorithms, the insulator defect detection has received more and more attention. However, there are still existing some difficulties: insufficient samples and low detection accuracy. To improve the accuracy of insulator defect detection, this paper proposes an auto-detection method based on an improved lightweight YOLOv5s model. First, this paper introduces the basic network frame of YOLOv5s and proposes an improved algorithm by utilizing the GIoU loss function, Mish activation function, and CBAM module. Then, performs data enhancement in the insulator dataset to enhance the robustness of the model. Finally, trains and tests the improved YOLOv5s model, and compares it with traditional target detection algorithms. Compared with traditional target detection algorithms, the AP value of the proposed algorithm in detecting insulator defects can be improved by 5 %. The results demonstrate the improved algorithm proposed in this paper can effectively identify and position the insulator defects. [ABSTRACT FROM AUTHOR]

• The feasibility of the ICOG corona ring is verified by simulation analysis. • The opening distance, installation orientation and insulating layer thickness of the opening corona ring are simulated and analyzed, and the parameters of the ICOG corona ring are determined. • The electric field of the ICOG corona ring in the case of bird droppings is simulated and analyzed. • Through the bird droppings simulation test, the anti-bird performance of the ICOG corona ring is verified. In the bird-related faults of transmission lines, the bird droppings flashover fault caused by the short-circuiting of bird droppings to the corona ring is extremely significant. To decrease the flashover probability of bird droppings and improve the convenience of installation, this paper proposes a method of coating the insulating layer on the open-gap corona ring, and verifies the insulation performance of the insulation coated open-gap (ICOG) corona ring through simulation and experiment. In this paper, the feasibility of corona ring coating insulating layer is verified by finite element simulation, and the influence of ICOG corona ring structure on the surface electric field distribution of composite insulator is studied. Finally, the impact of various bird droppings parameters on the flashover of the ICOG corona ring is investigated through experiments and compared with the flashover of an ordinary corona ring. The simulation results show that when the opening distance is 50–70 mm, the opening is toward the tower side, and the thickness of the insulating layer is 5 mm, the surface field strength of the composite insulator is the smallest. The experimental results show that the flashover probability of bird droppings increases with the increase of conductivity and viscosity of bird droppings. After the open-gap corona ring is coated with the insulating layer, the area where the bird droppings flashover occurs is reduced by about 20 %, which can better play the role of anti-bird flashover and has better convenience. This paper provides a certain reference for the anti-bird control of transmission lines. [ABSTRACT FROM AUTHOR]

This paper presents a new, improved approach to fault location in long and very long transmission lines, which uses measurements at both terminals of the line that do not need to be synchronized, using the satellite time-reference. The new method employs symmetrical component sequence voltage profiles that are computed using an innovative approach in which the detailed three-phase model of a multiconductor transmission line is represented as the series connection of several chain matrices. This allows the new method achieve the best performance, when compared to other 4 similar fault location approaches, requiring measurements at both terminals of a symmetrical line, considering all types of faults, under realistic variations in variables and parameters of the test system, including the effect of saturation of current transformers, and arc faults. The main advantage of this proposed technique is that it can be applied with no major changes in symmetrical and unsymmetrical transmission lines keeping its good performance. In addition, division of the line in chain matrices allows the new proposed approach to be applied in non-homogeneous lines. In this paper, for space reasons, the new approach is initially applied to symmetrical (ideally transposed) transmission lines only, with very successful and encouraging results. • This approach considers the detailed model of a multiconductor symmetrical line. • It achieves the best performance of all the considered algorithms of this type. • It was tested successfully considering 15 different realistic conditions. • Measurements do not have to be synchronized. • The simplicity of the algorithm, make it adequate to be implemented in a relay. [ABSTRACT FROM AUTHOR]

• Protection for inverter-based resources (IBRs) based systems has many challenges. • Developed superimposed quantity-based protection elements for a system with IBRs. • Protection elements are tested in a modified IEEE 9-bus system. • Evaluated system resilience with various maximum current limits in PV controllers. The increasing penetration of inverter-based resources (IBRs) to the power grid brings challenges to protection systems. IBRs may not provide sufficient fault current to trip protective relays, leading to delays in fault isolation and increased risk of equipment damage. To overcome the challenges, superimposed quantity-based elements are developed in this paper for transmission line protection in a power grid with IBRs. The characteristics of the designed protection system are tested under fault conditions in a modified IEEE 9-bus system that includes solar photovoltaic (PV) generation, and evaluated with different maximum current limits in solar PV controllers. The applied method in this paper makes contribution to the protection application for IBR-penetrated transmission systems. Simulation results show that the modeled protection system works effectively with different penetration of solar PV, and the system resilience is enhanced under fault conditions considering the tripping response and reclosing of circuit breakers. [ABSTRACT FROM AUTHOR]

This paper investigates the impact of earth continuity conductor (ECC) placement in duct banks for triangular and flat configurations of three-phase single-core underground cables using the single-point bonding method. Several works in the literature suggest that the ECC should be placed on the right side of the duct/trench for half of the underground transmission line (UGTL) and on the left side for the remaining length, implying the necessity of ECC transposition. However, this technique poses significant civil engineering challenges, requiring extensive work that increases the cost and construction time of the UGTL. Therefore, it is essential to propose a better ECC position that mitigates these problems while satisfying electrical, civil, and safety requirements. To address these issues, this study proposes a better ECC position that meets electrical, civil, and safety requirements while minimizing induced voltage on the sheath and induced current in the ECC. We focus on an underground transmission line operating at 220 kV, evaluating both triangular and flat configurations. The paper employs accurate formulations for the series impedance calculation of the cable and computes the induced factors under steady-state conditions, considering practical aspects such as civil works and ease of installation. Our findings indicate that in triangular formations, the optimal ECC position is precisely in the middle of the cables. This placement minimizes induced current and voltage on the sheath, eliminating the need for ECC transposition, contrasting with IEEE 575 guidelines. Conversely, ECC transposition is crucial for flat formations to minimize circulating current. Our study recommends placing the ECC at the top of the duct at a specific distance, differing from IEEE 575 and CIGRE 531 guidelines. When ECC transposition is performed, the induced voltage on the sheath can be calculated as if the ECC were not present. • Investigated optimal ECC placement in a duct for 220 kV underground lines. • Found that in triangular formation, mid-position ECC minimizes sheath voltage. • Contrasted findings with IEEE575, show optimal ECC position deviates from guidelines. • In flat formation, crucial ECC transposition identified, place ECC at duct top. • ECC transposition allows sheath voltage calculation as if ECC absent. [ABSTRACT FROM AUTHOR]

The lightning performance of transmission lines is a criterion of utmost importance to be evaluated in transmission system reliability. In order to accurately estimate the expected number of shutdowns, it is imperative to account for the stochastic nature of the lightning phenomenon. In this sense, the most widely used technique to estimate these shutdowns is the Monte Carlo method (MCM). Although the MCM is a trustful method, it has a huge drawback in terms of computational burden. Therefore, this paper proposes the use of an alternative statistical technique, the Unscented Transform method (UTM). This method achieves an approximate non-linear mapping by employing a set of points (associated with input statistical data), which are deterministically selected and weighted. The set of these points and weights is then used to estimate the lightning overvoltage across insulator strings, which represents a significant reduction in the number of samples evaluated in the process in relation to the application from MCM. In this paper, the MCM and UTM methods are applied and compared in the lightning overvoltage evaluation, which is carried out with the help of the Alternative Transient Program (ATP). From the studies conducted, it was found that the application of UTM in place of MCM allowed for significant computational gains while maintaining satisfactory levels of accuracy in the estimation of indicators. • Unscented Transform applied to transmission line lightning performance estimation. • Monte Carlo applied to transmission line lightning performance estimation. • Accelerating the assessment process of transmission line lightning performance. • Monte Carlo and Unscented Transform performance in lightning-related study. [ABSTRACT FROM AUTHOR]

Interline DC Power Flow Controllers (IDCPFC) plays a crucial role in Multiterminal-High Voltage Direct Current (MT-HVDC) systems for balancing the DC power flows in transmission lines. Conventional methodologies generally rely on single-stage topologies for IDCPFC, but their applicability to high voltage contexts is constrained by limitations in device ratings and susceptibility to electromagnetic interference (EMI). In interconnected networks with varying lengths of transmission lines, each line exhibits unique resistance levels, complicating the efficient achievement of voltage specifications. This paper presents to introduce a new high-voltage multi-terminal modular solid-state transformer (SST) based IDCPFC topology. The objective of this proposed topology is to expand the voltage range of IDCPFC to enhance power flow control within the MT-HVDC network. In order to minimize the switching losses of the proposed topology and validate its bidirectional feasibility, various modulation schemes are adopted. A thorough comparison of losses between conventional bidirectional topologies and the proposed topology is presented to demonstrate its effectiveness. The proposed control method is simulated on four cascaded modules based on case study of three nodes 500 MW system. The simulated results are further validated through experimental setup with two cascaded modules of 600 W. • This paper introduces a high-voltage multi-terminal modular solid-state transformer (SST) based IDCPFC topology, aimed at expanding the voltage range to enhance power flow control within the MT-HVDC network. • Various modulation schemes are proposed to minimize the switching losses of the topology while maintaining its bidirectional feasibility. • A thorough comparison of losses between conventional bidirectional topologies and the proposed topology is presented to demonstrate its effectiveness. • The proposed control method is simulated on a four-module, three-node 500MW system and validated through an experimental setup with two 600W cascaded modules. [ABSTRACT FROM AUTHOR]

• A method to correlate indirect lightning strokes and flashovers is presented. • The method focuses on the ratio between current peak and distance from the line. • The results provided by Rusck's and Darveniza's formulas and LIOV code are compared. • The minimum collecting area for calculating the lightning performance is addressed. Lightning location systems provide an estimation of both lightning current peak amplitudes and stroke locations, which are useful information to correlate lightning strokes and faults in power distribution networks. The paper presents a novel method for assessing the correlation between a lightning-induced flashover and the lightning current-peak-to-distance ratio of indirect lightning events. This is motivated by the consideration that a minimum threshold/value of the ratio between current peak and stroke distance from the line must be reached for an insulation flashover to occur. The proposed procedure uses existing equations and models that relate induced voltage peak amplitudes, distance, current peak and other parameters. Specifically, the paper compares the results predicted by Rusck's and Darveniza's formulas with those provided by the more detailed model implemented in the LIOV code. It is found that a minimum lightning current-peak-to-distance ratio must be exceeded to trigger an insulation flashover and that Rusck's and Darveniza's formulas may be too conservative in estimating such a threshold value. The paper provides guidelines for properly estimating the minimum collecting area around the line including all hazardous events, as this information is essential for calculating the lightning performance of a power distribution line using a Monte Carlo-based approach. [ABSTRACT FROM AUTHOR]

• This research paper proposed a novel computational technique for evaluation of the corona generated ionized electromagnetic field environment which initiates serious ill health environment under EHV/UHV DC transmission lines. • The proposed new computational technique was developed by modelling the dynamic behavior of the corona discharge phenomenon using gas ion bimolecular collision theoy concept which offers program less simple equations. • This developed computational technique offers unique equation solution which estimates corona generated ionic currents for any existing and upcoming HVDC transmission lines. This new computational analysis offers economical benefits to the line design engineers. • Actual experimental investigations are carried out at extra and ultra high potential levels to validate the accuracy of the proposed computational technique. • The proposed computational technique offered high computational accuracy compared to other techniques which are proposed elsewhere in the world and the computed results shown exact measured values. Corona on UHVDC transmission line conductors initiates corona power loss and the inevitable ionic current flow environment at ground level. To limit this substantial flow of ionic current at ground levels, it is necessary to establish an appropriate line design configuration, including the diameter of the line conductor and the height level above the ground. It is a tedious and expensive process to establish this appropriate line design solely based on experimental findings. Hence, the computational based numerical analysis with the support of final experimental validation aids in arriving at a safe and optimal transmission line design dimension configuration. Thus, the ionic current flow environment of UHVDC transmission lines may be characterized by ionized space charge density, ionic current flow, and electrical field distribution. To estimate this ionic current flow, it is necessary to estimate the ionized space charge density in the ionization region, which incorporates the solution of the Poisson's equation. It is intricate to solve Poisson's equation with known boundary conditions: as ionization process depends on the atmospheric parameters also. Multiple computational techniques are developed to estimate the corona generated ionic current environment under the HVDC lines by waiving these atmospheric parameter effects and claims the lack of computational accuracy. In this paper, the unipolar corona equation, usually called Poisson's equation was solved by estimating the space charge ion density using the concept of gas bimolecular collision theory. The gas bimolecular collision theory inculcates the procedure to estimate the collisional reaction rate constant between the gas molecules at given atmospheric temperature and pressure parameters. Therefore, this paper developed a unique equation solution for the estimation of transition of the ionic current magnitudes at known atmospheric temperature and pressure ambient conditions. This unique equation solution prevents the multiple actual testing procedures offers to obtain safe and optimal line design dimension configurations. Multiple experimental studies are carried out up to ± 900 kV to compare the computed results in the outdoor and indoor climatic conditions at the ultra-high voltage laboratory, CPRI. Also, the computed results are compared with the results published in the literature. Based on the comparison of results, the developed computational technique exactly matches the experimental results and claims improved accuracy compared to other computational techniques. [ABSTRACT FROM AUTHOR]

The proliferation of converter-interfaced generation necessitates the investigation of novel small-signal multi-machine interactions. The flexibility and lack of standardisation of converter control approaches results in a plethora of potential implementations, bringing different dynamics that can interact with each other and existing elements of the power system. This paper performs a small-signal analysis of power systems with the inclusion of grid-forming and grid-following converters for varying combinations of common control architectures, in terms of cascaded control loops, within the literature. Investigations are performed for a two-machine system and the WSCC 9-bus (three-machine) system. As well as interaction identification and characterisation, the impact of varying transmission line lengths, system loading, and generation dispatch are investigated. • Small-signal multi-machine interaction identification and analysis. • Comparison of different grid-following and grid-forming cascaded controllers. • Impact of system parameter variations. • Results highly depend on specific system layout, operating point, and controllers. [ABSTRACT FROM AUTHOR]

Electric demand and renewable power are highly variable, and the solution of a planning model relies on capturing this variability. This paper proposes a hybrid multi-area method that effectively captures both the intraday and interday chronology of real data considering extreme values, using a limited number of representative days, and time points within each day. An optimization-based representative extraction method is proposed to improve intraday chronology capturing. It ensures higher precision in preserving data chronology and extreme values than hierarchical clustering methods. The proposed method is based on a piecewise linear demand and supply representation, which reduces approximation errors compared to the traditional piecewise constant formulation. Additionally, sequentially linked day blocks with identical representatives, created through a mapping process, are employed for interday chronology capturing. To evaluate the efficiency of the proposed method, a comprehensive expansion co-planning model is developed, including transmission lines, energy storage systems, and wind farms. • Transmission and generation expansion problems are often based on time series. • Time series aggregation methods are used to reduce computational complexity. • We propose to use representative days with adaptively selected representative hours. • The efficiency is improved by using a piecewise linear dispatch representation. • Long-duration energy storages are modeled by tracking the daily state of charge. [ABSTRACT FROM AUTHOR]

The key of traveling wave (TW) fault location (FL) method is the calculation of TW velocity and the calibration of TW wave head. In order to achieve high-precision FL, detailed transmission line (TL) parameters are needed to accurately calculate the TW velocity. In view of the problem that the existing high-precision TWFL methods are highly dependent on the calculation of TW velocity, the paper contributes to following aspects: (i) the mapping relationship between wavefront frequency and fault distance/fault pole is constructed; (ii) a neural network model suitable for FL and fault pole identification is designed, which is optimized by Particle Swarm Optimization (PSO) algorithm and Levenberg–Marquardt (L-M) algorithm; (iii) a complete FL scheme is proposed. In order to verify the FL accuracy of proposed method, an ± 800 kV bipolar high-voltage direct-current (HVDC) transmission system model is constructed using PSCAD/EMTDC. According to the simulation results, the errors of FL is less than 0.2 km and the accuracy of fault pole identification is 100%. For the problems of fault type, fault resistance and noise, the proposed method shows high robustness. • The relationship between frequency and fault location/fault pole is constructed. • Not depend on transmission line model parameters. • Higher fault location accuracy. • Robust against fault resistance. [ABSTRACT FROM AUTHOR]

Vulnerable transmission lines are one of the weak links in the operation of the power system, as their damage can trigger widespread blackouts and cascading failures. The integration of large-scale wind power generation into the grid has resulted in significant changes to both the topology and distribution patterns of power flows inside the system, exacerbating line vulnerabilities. Identifying these lines can enhance power system safety through vigilant monitoring or augmenting their carrying capacity. In this paper, a method for identifying vulnerable lines based on the theory of topological potential is proposed. The method is based on the N-1 fault model of optimal DC power flow, and a corresponding network is constructed for the power system. The task of pinpointing weak points in a complicated network is converted into an assessment problem of important nodes. The proposed index comprehensively considers the in-degree and out-degree topological potentials of nodes, and uses the entropy weight method for weight allocation. Meanwhile, the TLS distribution is used to fit the wind power prediction error. Finally, simulation experiments are conducted on the IEEE 39-bus system. Simulation results indicate that the most vulnerable transmission lines tend to be located at the hubs of the system's topological network and in close proximity to wind farms. • The proposed method maps the power system into a complex network using an N-1 contingency model. • To better reflect the real situation of the power grid, the method adopts optimal DC load flow dispatch. • To consider the uncertainty of wind power output, the method utilizes TLS distribution to fit the error of wind power output. • Simulation results indicate that lines near wind farms and topological hub structures are often most susceptible to faults. [ABSTRACT FROM AUTHOR]

In recent years, there has been an exploration of innovative electric grid concepts centered around power routers, devices capable of controlling power flows as desired. One of which is the Power Router Grid, a novel high-controllable network design fully based on power routers. Its ability to arbitrarily change power flows inside controllable lines raises the challenge of determining the optimal operation within such systems. This paper aims to push further the analysis of the operation and benefits of such networks by proposing a novel optimization model tailored for power router grids based on the most recent literature for the convexification of optimal power flows. Moreover, it demonstrated that radial-based models can be expanded for grids meshed through power routers. The model presented is also convex in the form of a second-order cone, ensuring a global optimum for diverse grid configurations. It has been implemented in Python using the PYOMO modeling language and applied to three case studies investigating the effects of power router operation modes on the grid's optimal operation and associated costs. Results show that the definition of the power router grid design and the ports operation mode must be carefully decided when demand uncertainty of over 25% is taken into consideration. Moreover, controlling power flow near lines of higher impedance can lead up to a 21% increase in line losses. • A novel and linearized optimal power flow model for electric grids based on power routers. • Application of second-order cone convexification for grids meshed through power routers. • Analysis of the effects of the layout and power controllability in line losses inside the power router grid. • Implementation of the optimization model in pyomo. [ABSTRACT FROM AUTHOR]

• Inaccuracy of fdLine model in simulating transients in TLs with underbuilt wires assessed. • Higher errors in 100 kHz-1 MHz range, linked to lightning overvoltage wavefronts. • Errors increase with soil resistivity; up to 25 % difference in peak transient voltages. • Prefer ULM over fdLine for transient analysis in TLs with underbuilt wires using EMT programs. This paper investigates the potential inaccuracies associated with using a modal-domain model featuring a real and frequency-independent transformation matrix in simulating electromagnetic transients on power overhead lines equipped with underbuilt wires. Three transmission line configurations are examined: one without underbuilt wires, one with a single underbuilt wire, and another with two underbuilt wires. Comparisons between the simulated voltages computed using the modal-domain approach and a more accurate phase-domain model as a reference reveal that the modal-domain approach leads to inaccuracies in the simulated voltages. These inaccuracies intensify with an increase in the number of underbuilt wires and the soil resistivity. Differences of up to approximately 24 % in the peak values of the simulated voltages were observed, considering the transmission line geometry analyzed in this study. Based on these findings, it is recommended that for simulating transients in overhead lines with installed underbuilt wires, phase-domain models, such as the Universal Line Model, should be employed. [ABSTRACT FROM AUTHOR]

This paper leverages the shape of current traveling waves to enhance transmission line protection. It investigates the distortion effect on the traveling waveshape during propagation along the transmission line. It focuses on utilizing the ratio of area to the peak of the initial traveling wave at the local end to estimate the level of distortion and identify faults within the protection zone. This eliminates the need for arrival time information of initial waves, detection of subsequent traveling waves, and synchronized data communication from the remote end. Effectiveness of the proposed method is evaluated through simulations of faults in a 400 kV transmission network and real-time testing on the RTDS Novacor simulator. The ratio of area and peak, being less affected by the fault resistance and variation in inception angle, the proposed method offers more reliability for traveling wave-based line protection compared to available techniques. • Shape of current TWs are analyzed. • Area and peak of the waveshape are utilized for line protection. • Only Initial TWs are utilized and detection of subsequent reflected TWs not required. • Performance is promising for wide variety of faults. [ABSTRACT FROM AUTHOR]

This paper presents a novel backup protection scheme integrated with fault location capabilities for unsynchronized three-terminal multisection hybrid untransposed double-circuit transmission lines. The proposed non-iterative scheme fully considers the distributed nature of line parameters along with couplings between phases. Initially, upon activation of this scheme, a new technique for discerning internal faults from external ones and other disturbances is proposed. It effectively overcomes the limitations of existing scheme for faults close to Tee-point (T-point) when terminals are unsynchronized. Subsequently, the faulted branch, section and phases are identified using the developed algorithm. The performance is evaluated for different external and internal intra-circuit and inter-circuit fault cases. Performance comparison is conducted to explore the superiority of the proposed scheme over existing approaches in switch-on-to-fault cases and faults occurring in close proximity to the T-point. Furthermore, the scheme's robustness is assessed under different variations in fault types, fault locations, fault resistances, line parameters, and synchronization angle errors through Simulink/MATLAB simulations. Obtained simulation and experimental results reveal the efficacy of proposed scheme over recently reported schemes. • Backup protection for unsynchronized three-terminal multisection transmission lines. • Utilization of online phasor measurements of voltages and currents for switch-on-to-fault cases. • Reliable detection of faults close to T-point utilizing unsynchronized measurements. • Superior performance compared to prevailing schemes. [ABSTRACT FROM AUTHOR]

• A broken overhead earth wire increases the risk of pole high earth potential rise. • Following a strict design diagram is crucial to achieving safety compliance. • Split factor in high-voltage transmission lines is crucial for safety compliance. An electrical high-voltage power system is essential to support everyday electrical demands. Due to the increase in electrical loads, a more rigid design is required to ensure system compliance with standards and policies. High-voltage safety is the number one priority when it comes to the design, installation, commissioning, and operation of the electrical power system network. Safety compliance is getting more complex due to the joining infrastructure between residential and high-voltage projects. Nowadays, high-voltage infrastructure, including substations and transmission lines, is constructed near residential properties. This neighboring setup increased the safety concerns of high voltage systems, especially under fault or system malfunction situations. Safety concerns are addressed during the design stage and verified during the commissioning stages. The paper discusses the minimum transmission line earthing system requirements. This document provides a clear and consistent approach to assess transmission line earthing system design. The work contents comply with current IEEE standards including rigid author research outcomes. The works reduce the complexity of the assessment and explain the critical role of different sectors within the transmission line network. The work introduces the boundaries when the fault current analysis should include the earth grid resistance. A case study is also included. [ABSTRACT FROM AUTHOR]

Dynamic line rating techniques are increasingly prevalent in the computation of ampacity for overhead transmission lines. Some of these methods, commonly employed by system operators, rely on real-time measurements to calculate conductor temperature, either directly or indirectly. Despite their widespread usage, the susceptibility of these techniques to measurement errors has been largely disregarded in prior research. In this regard, this paper includes a groundbreaking reliability analysis addressing the impact of measurement errors on various dynamic line rating techniques in overhead lines, based on conductor temperature estimation. Two case studies are presented, incorporating typical errors from simulations. The first case study adopts a standard 24-hour profile for the variables involved in the conductor ampacity calculation. In the second study, Monte Carlo simulations are conducted, in which meteorological variables are randomly assigned with five load levels to evaluate the current's influence on measurement noise sensitivity. The resulting ampacity errors across all methods considered are remarkably high, with mean values exceeding 150% in specific scenarios. This unequivocally demonstrates that the commonly accepted levels of measurement accuracy in these widely used rating techniques yield estimations falling far below acceptable reliability standards. • Reliability assessment of DLR methods based on conductor temperature evaluation. • Daily profile for the temporal evolution of estimation errors in estimated DLR. • Monte Carlo simulations for statistical characterization of errors. • Unacceptable errors under typical measurement errors. [ABSTRACT FROM AUTHOR]

• When the direct current voltage of the conductor and the electric field of thundercloud act together, the positive wire inhibits the corona discharge of the upper ground wire, while the negative wire enhances the discharge of the upper ground wire. • The influence of air humidity on corona discharge on the shield wire surface above the negative conductor is greater than that on the shield wire above the positive conductor. • The corona discharge current on the shield wire surface above the negative pole wire does not change much whenthe downgoing pilot channel is considered, but the corona discharge on the shield wire surface above the negativepole wire is intensified by the presence of natural wind, and the corona current value gradually increases. The atmospheric space electrical field has nonlinear distribution characteristics during thunderstorm activity, which influences the ground surface electric corona of UHV transmission lines. In this paper, the corona discharge model of ground wire of ±1100 kV UHVDC transmission line is established considering the combined effect of ground lightning process and working voltage. With the combined action of thundercloud electrical field and DC voltage, the positive conductor suppresses the electric corona of the upper shied wire, and the negative conductor enhances the discharge of the upper shied wire. The corona current of the right shied wire is 54.7 μA/m larger than that of the left shied wire. When the down leader develops, the leader voltage, the line operating voltage and the thundercloud voltage work together, and the electric corona on the surface of the conductor and shied wire of the transmission line increases rapidly. The corona current increases 102 times on the left shied wire's surface and 103 times on the right shied wire's. Considering the environmental factors and the development of the downgoing leader at the same time, the degree of electric corona on the surface of the shied wire is weakened when the humidity in the space increases, but the overall value of the corona current is much higher than the thundercloud electrical field. When the wind speed increases, the degree of electric corona on the surface of the shied wire is aggravated. The corona current on the surface of the left shied wire is 37.13 μA/m, and the one of the right shied wire is 109.33 μA/m. The corona current value of ground surface increases with the increase of wind direction. [ABSTRACT FROM AUTHOR]

• Method builds on power flow solutions to compute power flows components. • Designed for meshed networks, adept at managing shunt elements. • Illustrated with 4 examples showcasing results obtained with the method. • Load can't rely solely on nearest power source, even if local generator meets demand. • Implementation in Python, code accessible on github.com. To thoroughly analyze the conditions in power lines, transformers or loads, it is essential to have knowledge of their active and reactive power flow contributions from each power source. Understanding these contributions allows for a detailed analysis of the impact of active and reactive power flow contribution from each power source on active and reactive power losses in each network element, as well as the determination of power participation of each source to every load. This paper provides the necessary equations and an adequate procedure for calculating power flow contributions. The method is suitable for meshed network and considers shunt elements, avoiding problematic simplifications. Furthermore, it ensures impartiality towards any network user, making it well-suited for application in deregulated environments. By offering valuable information useful, this method supports the creation of transparent and non-discriminatory agreements between network operator and users. [ABSTRACT FROM AUTHOR]

Flexible DC Transmission Systems (FDCTS) devices offer the most promising solution for Power Flow Management (PFM) problem in complex meshed MTDC grids. This paper proposes a new formulation for steady state analysis of a MTDC grid, integrated with the multiport version of the FDCTS device called Multiport Interline DC Current Flow Controller (MIDCCFC). MIDCCFC can regulate the current flow of two or more lines, thereby achieving line power flow regulation and aid for DC line breaking in a MTDC system. The proposed formulation integrates the steady state operating point of MIDCCFC with the MTDC system. The proposed formulation is tested on a 5 bus 320 kV meshed MTDC grid with 5-port MIDCCFC. A criterion is evolved to ensure the feasibility of the operating point obtained from the proposed formulation. The line current regulation range offered by MIDCCFC for line-12 in the test system is (30-3086) A. The impact of line-12 current variation on the system variables over the obtained range is investigated. The application of MIDCCFC for DC breaking is also investigated. The results are validated by performing steady state simulation of the test system in MATLAB/Simulink and real time simulation of the test system in Real Time Digital Simulator. [Display omitted] • Formulation of Power flow model for MIDCCFC integrated meshed MTDC system. • Application of Newton–Raphson based iterative algorithm for DC power flow analysis of MTDC system with MIDCCFC. • Criteria for feasible existence of the steady state operating point. • Validation of the power flow results in real-time using Real Time Digital Simulator (OP4510). [ABSTRACT FROM AUTHOR]

• This paper proposes a novel fast time-domain protection scheme in a large-scale PPP system, with prominent features such as simplicity. • There is no need of parameters tuning because of the adaptive nature of ITD. Also, all the protection scheme parameters are determined analytically, such as threshold value and number of iterations. • A wide variety of fault scenarios are analyzed for fault detection such as different fault resistance, location and types. • Communication medium is not required. Consequently, there is no communication delay and data loss. • The protection scheme's capability in various conditions such as noisy environments, uncertainty in renewable energy generation, change in GC, various sampling frequencies and CT saturation is discussed. • The proposed protection scheme is tested in two the 2-bus and IEEE 39-bus test systems in MATLAB and PSCAD environments. The performance of a distance relay can be significantly affected by various uncontrolled factors such as fault resistance, fault type, fault location and noise. Moreover, when photovoltaic power plants are integrated into electrical grids, they exhibit distinct fault current characteristics compared to conventional power systems with synchronous generators. These factors introduce variations in the recorded apparent impedance, deviating from the predefined settings of the distance relay. This paper presents an effective scheme for fault detection using ITD methodology. The ITD method decomposes the target signal into proper rotation and monotonic signals, which are then used to calculate the Energy Index. The performance of this scheme has been extensively investigated under various scenarios, including fault resistance, fault location, fault type, CT saturation, GC compliance, noise, and sampling frequency. To validate the effectiveness of the proposed scheme, simulations are conducted using both the PSCAD/EMTDC and MATLAB software. The proposed scheme is assessed using both the 2-bus and IEEE 39-bus test systems. The results show the merit and effectiveness of the proposed scheme in the accurate diagnosis of fault detection with 400 Ω fault resistance, in the presence of 20 dB noise, with variable sampling frequency (0.5-16 kHz) and variable irradiance values (600-1000 (W / m 2)) in power systems. [ABSTRACT FROM AUTHOR]

• The experiment observed, recorded and analyzed the natural icing process of insulators, but most of the previous studies were simulated in the laboratory. • This paper analyzed the icing process of different types of insulators (shed structure, Shed diameter) under natural icing environment. • The influence of wind speed, humidity, precipitation and temperature on the natural icing process were analyzed. • Based on the final icing morphology under natural condition, this paper took the of icicle number, icicle length, icicle diameter, icing thickness of shed surface and icing mass as characteristics, analyzed the differences in icing results of different structures insulators, and got the conclusion (4), which provides reference for insulator selection of transmission lines in icing areas. Icing flashover of insulator strings has always been a serious factor threatening the safety and stability of the power grid. Researchers have simulated icing based on an artificial climate chamber, but it cannot fully simulate the growth process of insulator strings during the icing period in the natural environment. The icing growth characteristics of insulator strings in the natural environment are not clear. In this paper, three kinds of porcelain insulators were tested in the Xuefeng Mountain natural icing test base of Chongqing University. The results show that the freezing rain, alternating icing of freezing rain and freezing fog can cause the insulator stings to form glaze and mixed rime, and the icing degree on the windward side is more serious than leeward side. The higher the test environment's precipitation, humidity and wind speed, the faster the insulator strings' icing speed. And there are also some influences of the ambient temperature on the icing morphology in this test. The icing thickness on the windward side of the insulator shed will gradually increase. The number of icicles of insulators is positively correlated with the diameter of insulator sheds. The icing mass of insulator strings is seriously affected by their shed structure. [ABSTRACT FROM AUTHOR]

• Blackouts bring major economic and societal repercussions. • Efficient black-start strategy is critical to address increasing risk of blackouts. • Variable speed hydro can provide a fast response and is used during black start. • Meet black start needs with renewables and cutting diesel use. • RES-BESS boosts power and fortifies an integrated renewable grid. A blackout refers to a total power outage that rapidly plunges the electrical power system into a severe crisis, posing significant challenges for subsequent restoration efforts. Blackouts can occur due to a range of factors, such as delays in clearing faults, generator malfunctions, equipment failures, and human errors. After a blackout occurs, all possible measures are taken to achieve the fastest power system restoration. To ensure preparedness for such emergencies, scheduled black start exercises are conducted using units capable of initiating power restoration from scratch, allowing authorities to assess their readiness in catastrophic scenarios. Numerous similar exercises have been conducted regularly generating to highlight the complexities of power system restoration of the grid with the black starts of hydro generating units. This has aided plant operators in improving restoration methods and finding additional remedial steps to enhance existing processes to achieve an effective black start exercise. This paper overviews the multiple mock black start exercises applied to hydroelectric generating units and discusses several blackouts worldwide. In addition, Tehri Hydro Power Plant is considered for the case study. Tehri HPP is linked to the 400 kV EHV grid, which was later upgraded to 765 kV transmission lines. Further, this paper observes and discusses various challenges encountered during mock black start exercises. Possible remedial actions are suggested to address these challenges. [Display omitted] [ABSTRACT FROM AUTHOR]

• Proposed a protection scheme can determine the fault type only by calculating the similarity of one-mode current. • Based on the principle of one-mode current similarity, offering a viable solution to address the challenges arising from weak-infeed, frequency offset, and phase uncertainty caused by the LVRT strategy of the new energy station. • Proposed a protection scheme has good adaptability when the wind farm operates independently, and can also adapt to different wind farm capacity and energy storage ratio, which has certain application prospects in practical engineering. With the gradual growth of the scale of energy storage devices for wind power generation, a large-scale grid-connected wind-storage combined system (WSCS) has been formed. When the external transmission line fails, its control strategy will lead to problems such as limited output short-circuit current amplitude, frequency deviation from power frequency, and uncertain phase angle, which makes the traditional pilot protection possible to malfunction and refuse to operate. In order to solve this problem, this paper first analyzes the fault current output characteristics of the WSCS during low voltage ride through (LVRT), and its impact on the traditional pilot protection scheme. Secondly, considering the difference of fault current amplitude and phase change at both sides of the transmission line, the similarity relationship of one-mode current is verified. Finally, a pilot protection scheme based on one-mode current similarity is proposed in this paper. The simulation results conducted using PSCAD/EMTDC demonstrate that the proposed scheme exhibits robust anti-interference capability, capable of withstanding significant transitional resistance and noise, while maintaining good selectivity and reliability. [ABSTRACT FROM AUTHOR]

This paper aims at assessing the relevance of the coupling effects among the main components of overhead power lines in their lightning response, namely, tower, grounding electrodes, and shield wire(s). Mutual coupling effects are investigated by simulation, using an electromagnetic model. The analyses are performed in the frequency and time domain, by considering, respectively, the input impedance at the node of current injection and the overvoltages rising at the same node. The study is conducted considering different configurations for current excitation and three arrangements of grounding electrodes, with the corresponding soil properties. From the analysis of the results, it appears that the effects of electromagnetic coupling among the considered system components affects only marginally the lightning response of the line, being much less relevant than the effects of the uncertainties on the values of electrical parameters of the local soil. This confirms the validity of the macromodeling approach and denotes that the accuracy of the results is overall dependent on the suitability of models adopted for each component; in particular, the proper representation of the grounding system is proven as essential to the successful prediction of overvoltages at the tower top. • Electromagnetic (EM) coupling among main components of overhead lines is studied. • A typical transmission line tower hit by a lightning current is considered. • EM interactions among tower, shield wire, and grounding system (GS) are limited. • Tower-to-shield wire EM coupling mainly influences the computed input impedances. • Macromodeling can be adopted, yet towers and GSs should be conveniently modeled. [ABSTRACT FROM AUTHOR]

Expanding electrical transmission networks is a critical challenge faced by many developing economies. This process requires extensive investments, which must be strategically and methodically planned on a large scale, often encompassing regional or national considerations. Differing from typical Network Design Problems, efficiency in a transmission network can sometimes be enhanced by strategically deactivating certain transmission lines. Thanks to that, this paper focuses on a version of the transmission expansion planning problem that allows redesign during the network expansion. We propose using two exact methodologies as alternatives to the direct use of mixed integer programming formulations with commercial solvers. These methods are an application of Benders' decomposition and a newly developed approach named Ring Space. Through comprehensive computational experiments, we assess and compare the efficacy of these methods against the conventional application of the mathematical formulation. Additionally, this study successfully obtained new high-quality solutions and proved their optimality for a subset of benchmark instances. • Two exact approaches to solve the Transmission Expansion Planning Problem with Re-design were proposed: (i) A new method called Ring Space. (ii) A Benders' Decomposition was developed and combined with Branch-and Bound for the first time for TEPr. • New optimal proved for a benchmark instance. • Improved the best-known solution for two benchmark instances. • Computational experiments illustrate the effectiveness of each method. [ABSTRACT FROM AUTHOR]

This paper introduces a time–frequency analytic method for the exact identification of wideband DQ impedance models oriented to harmonic stability of converter-driven systems with transmission line models with distributed and frequency-dependent parameters. Wideband models are of great importance in the analysis of harmonic stability over a broad range of frequencies. The transmission line is a crucial component in this regard, but it is not straightforward to incorporate it into the impedance model of AC power-electronics-based power systems. This has led to the use of lumped parameter models or models based on rational approximations. This article proposes a method to include this important element to the impedance model directly from its frequency domain model. Salient features of the proposed modeling approach include the frequency telegrapher's equations with distributed and frequency-dependent parameters, exact delay models of PWM, control implementations of power electronics, and an exact steady-state computation using a balance method based on a hybrid time–frequency approach. The proposal avoids time-domain simulations, rational approximations, or the fast Fourier transform. A converter-driven system with transmission lines is used to validate the proposal and the results of the frequency scanning method conducted in OPAL-RT (ARTEMiS/EMTP-RV) and PSCAD/EMTDC support the effectiveness, speed, and accuracy. • Accurate D Q impedance model of AC systems with frequency-dependent lines. • Impedance model, including lines, avoids rational and approximate models. • Steady state accurately computed using exact equations for lines and converters. • Characterization avoids time-domain simulations, FFTs, and analytical modeling. [ABSTRACT FROM AUTHOR]

This paper introduces a conceptual framework and infrastructure designed to monitor the dynamic behavior of the Brazilian Interconnected Power System (BIPS) following disturbances that affect power transmission in High Voltage Direct Current (HVDC) links. Monitoring is devised in light of a set of proposed System Severity Indicators (SSIs), whose computation depends upon synchrophasor data collected at converter stations and conveyed to a phasor data concentrator (PDC) placed in the control center of the Brazilian System Operator (BSO). Numerical results are acquired using electromagnetic transient (EMT) simulation and actual disturbance records, including cases with commutation failures and DC transmission line fault events. The results highlight the applicability of the proposed indicators on featuring the severity of events to the transient stability of the BIPS. • PMU-based framework to monitor systemic effects after disturbances in HVDC links. • Indicators are proposed to feature the event severity to system stability. • Results are acquired using EMT simulations and disturbance records. • Proposed approach is sufficiently generic to be adopted in large power systems. [ABSTRACT FROM AUTHOR]

Detection and identification of faults in large distribution systems with limited metering continue to pose significant challenges for system operators. The prevalence of installed phasor measurement units (PMUs) in power systems, provides an invaluable resource for fault detection and location. Therefore, there is a rich literature on methods that leverage the benefits of these PMUs for the purpose of event detection. However, a notable proportion of the proposed solutions assume the presence of one PMU at every bus, or at a large percentage of buses that will make the system observable. Despite concerted efforts to substantially increase the number of installed PMUs, majority of utilities have yet to attain comprehensive PMU coverage at the terminals of every transmission line. Thus, many of the proposed methods cannot be practically applied to existing power systems with limited number of installed PMUs. Consequently, the objective of this paper is to develop a method, aided by the application of Convolutional Neural Networks, to identify and precisely locate faults within a system, even when only a minimal number of Phasor Measurement Units (PMUs) are present. [Display omitted] • ANN approaches are shown to enhance fault detection capabilities for limited number of PMUs. • CNN model is shown to outperform MLP in terms of fault detection performance. • Placement of PMUs is shown to have a significant effect on the performance of fault detection. [ABSTRACT FROM AUTHOR]

• Cable coupling interferes with measurements of grounding resistance. • Low resistivity concrete enhances grounding performance. • Lightning wavefront times are important for grounding analysis. • Transmission line grounding shows inductive behavior. • Concrete electrode shows capacitive behavior. One of the main causes of outages in transmission lines is lightning. To mitigate this occurrence, grounding electrodes are used at the base of the towers that make up the transmission lines. Since lightning is a phenomenon with components of low and relatively high-frequency energy (approximately up to 2 MHz), there is a certain complexity in accurately characterizing grounding systems. The primary parameter used to model a grounding system is the grounding impedance, which can be obtained through measurement. This paper presents measurements conducted on a 138 kV transmission line's traditional and alternative grounding system. The measured traditional grounding system consists of two horizontally buried copper grounding conductors and the alternative system comprises an electrode with four conductors encapsulated in concrete and buried vertically. The measurements were carried out using a 25 kHz earth resistance meter and impulse generators with waveform shapes of 1.2/50 μs, 1/70 μs, and 8/70 μs. Different measurement configurations are employed. The obtained measurements are compared with similar systems found in the literature, and the contributions of the concrete electrode to the grounding system are discussed. [ABSTRACT FROM AUTHOR]

Metal OxideVaristors(MOV) are widely used as protective devices of series compensation capacitor banks for Extra-High Voltage and UHV (Ultra High Voltage) large capacity long-distance transmission lines. As MOVs work in the strong nonlinear part of the V-I curve, the aging and deterioration degree of different MOVs in parallel connection are different, leading to one or two MOVs in the entire heavy-duty group being the first to be damaged. The uniformity of current is an important criterion for how to control the power frequency shunting of multiple parallel MOVs for series compensation capacitor banks. In order to investigate whether replacing damaged MOVs with newly manufactured MOVs of the same specifications can meet the uniformity requirements, the power frequency reclosure tests are carried out with an average voltage peak of 166.3 kV on MOV group with 10 served and 1 new MOV for the first time with actual 500 kV MOVs. Research finds that when the DC (Direct Current) U 2mA mean absolute error of MOVs is 0.2%, the current mean absolute error is about 6%. After testing, the temperature rise of each MOV ranges from 22.9 to 36.3 °C. The test results in this paper provide a direct data basis for confirming the criterion of DC reference voltage and shunt uniformity at large power frequency current on actual 500 kV series compensation MOVs apparatus. [ABSTRACT FROM AUTHOR]

• Lightning current waveform effects on critical flashover currents are assessed. • Negative and positive first return-stroke current waveforms are considered. • Typical 150 kV and 400 kV double-circuit overhead lines are evaluated. • Statistical distributions of the CIGRE current waveform parameters are considered. • Impact of positive lightning strike parameters is more marked for backflashovers. This paper investigates the influence of the CIGRE lightning current waveform parameters on the computation of fast-front overvoltages and critical lightning currents causing flashover of overhead transmission line insulation. The investigation is conducted via ATP-EMTP simulations employing both negative and positive lightning current waveforms corresponding to first return strokes. Typical 150 kV and 400 kV double-circuit overhead lines are evaluated by performing shielding failure and backflashover simulations. The statistical distributions of the parameters required as input for the CIGRE lightning current waveform (front time, maximum steepness, time to half value) are considered in simulations to quantify and analyze their effects; this enables the comparison between negative and positive lightning strikes. The waveform parameters do not affect considerably the critical shielding failure flashover current for both polarities; the most influential parameter in this case is the time to half value. On the other hand, the wavetail duration influences the least the critical backflashover current; the latter is lower for waveforms with faster wavefront (lower front time and higher maximum steepness). The impact of the waveform parameters of positive lightning strikes is more marked for the backflashover case due to their larger variations compared with negative strikes. [ABSTRACT FROM AUTHOR]

Transmission line parameters are needed to be precisely known to ensure accurate power system analyses. In spite of various noise reduction methods, measurement noise can still affect the phasor measurement unit (PMU) data, leading to errors in the estimated parameters. A Kalman filter can be used to estimate these parameters from PMUs data which may suffer from noise. The existing methods often ignore the presence of noise in voltage measurements and therefore are vulnerable to errors when noise is presented in voltage measurements. In this paper, a new method that considers the noise in both voltage and current synchrophasors is introduced. A novel formulation for considering the voltage measurement noise is introduced when estimating transmission line parameters from PMU data. Consequently, an analytic derivation of the measurement noise covariance matrix for the Kalman filter is presented. Extensive simulation results demonstrate that compared to the existing methods, the developed formulation and the associated measurement covariance matrix significantly improve the accuracy of estimates. • Accuracy improvement of Kalman-filter-based estimation • Modified measurement noise covariance matrix for Kalman filter • Estimation of transmission line parameters using voltage and current synchrophasors • Considering measurement noises both in regression matrix and measurements vector • Derive covariance matrix using the latest estimation results and PMU measurements [ABSTRACT FROM AUTHOR]

• DC transmission lines can produce severe corona discharge and audible noise (AN) at high altitudes. • A climate tank test platform with adjustable air pressure and humidity was built in the paper. • The corona current pulse and AN data in the humidity range of 45 % to 90 % and the air pressure range of 78.9 to 56.04 kPa were obtained. • AN level increased significantly with decreasing air pressure and with increasing relative humidity, the changes were small. DC transmission lines can produce more severe corona discharge and audible noise (AN) at high altitudes than that in low elevation areas, which is an important factor to be considered in line erection and selection. Besides, the humidity can also affect the performance of corona discharge and AN level. In this paper, a climate tank test platform with adjustable air pressure and humidity was built, and the characteristics of positive DC corona discharge and AN level of stranded wire conductor were investigated. The corona current pulse and AN data in the humidity range of 45 % to 90 % and the air pressure range of 78.9 to 56.04 kPa were obtained, and the variation were analyzed. It is found that, as the air pressure decrease, the A-weighted AN level increase clearly. With the increase of relative humidity, the A-weighted AN level fluctuated, but the change is relatively small. [ABSTRACT FROM AUTHOR]

• Switching impulse discharge experiments of rod-plane air gaps with different front times and absolute humidity are carried out. • Corrected U 50% of different front times when considering atmospheric parameters and absolute humidity. • Analyzed the main influencing factors of air gap discharge time under different conditions. In long-distance transmission lines, the switching overvoltage waveform differs from that of ordinary lines. The wave front time is primarily distributed above 1000 μs. And the switching overvoltage waveform has an important influence on the design of external insulation. This paper aims to deeply study the effect of various factors on the discharge of air gaps under the long front switching impulse voltage. This paper selects three kinds of rod-plane air gaps, and the switching impulse discharge experiments with different front lengths and absolute humidity under positive polarity are carried out. The effects of front time T f , absolute humidity h , and gap distance d on the discharge characteristics of the air gap are analyzed. The results show that the U 50% of an air gap is positively correlated with absolute humidity, front time, and gap distance. When considering the additional influence of humidity, the humidity additional influence factor c and the atmospheric parameter influence index n at different front times are almost unchanged. With the increase in gap distance, the influence of front time on U 50% is more obvious. With the growth of the operating wave front time, the rising rate of U 50% tends to slow down. The discharge time of the air gap under different conditions is mainly determined by the front time. The research results can provide a theoretical and experimental reference for the influence of front time T f and atmospheric parameters on the discharge characteristics of air gaps under long front switching impulse. [ABSTRACT FROM AUTHOR]

The main contributions of this article are as follows: • Proposing a new DTLR prediction model based on knowledge-driven and data-driven. • Preprocessing of the data is done by using VMD combined with PACF. • Optimizing the hyperparameters of the BiLSTM model by the NGO algorithm. • Proposing an objective function to validate the effectiveness of the model. This paper developed a new algorithm to predict dynamic thermal line rating to increase the capacity of transmission lines, which can enhance the capacity of wind power integrated to the grid and reduce the curtailment. The proposed dynamic thermal line rating prediction model was trained by analyzing historical meteorological data and conductor physical parameters, and used deep learning with parameters optimized by an optimized algorithm. The prediction accuracy of the model is verified by Mean Absolute Error, R 2 and comparison with other models. The simulation results show that the proposed prediction model has a good performance. The suggested dynamic thermal line rating algorithm, which bears resemblance to the actual value, boosts the static thermal line rating by varying degrees of 23% to 75% at different instances throughout the sample. At the same time, this paper designs an optimal power flow economic dispatch objective function. By comparing the economic dispatch of the power grid calculated by adding static thermal line rating and the prediction models, the method proposed in this paper can effectively increase the amount of wind power integration and reduce power generation costs. [ABSTRACT FROM AUTHOR]

• An overview of traditional insulator defect detection methods. • The insulator defect detection method based on deep learning is highlighted. • The challenges faced and the future development directions are analyzed. Insulator is a kind of key electrical equipment in transmission line. Its long-term operation in strong electric field, high temperature sunshine, mechanical stress, humidity, dirt and other complex environment. This is likely to lead to self-detonation, pollution, flashover and leakage current and other defects, which will reduce insulation performance and seriously affect the safety of power grid. Therefore, power insulator defect detection is an important task in power system detection. How to identify insulator defects quickly and accurately has been an important problem for many scholars. Firstly, this paper reviews the insulator defect detection technology based on traditional detection algorithm. Secondly, the application and key technologies of deep learning algorithm in insulator defect detection are introduced in detail. Then it introduces the challenges and future development trend of this field; Finally, it summarizes this paper and puts forward some suggestions for the development of this field. [ABSTRACT FROM AUTHOR]

• BWO-FLANN model has been proposed for weight updation in the FLANN network. • NS-MOTLBO is proposed for solving the EELD issue in the predicted load condition. • One constraint handling approach is used for generating the Pareto solution. In this paper, the future load condition is predicted by proposing an effective single-layer Black Widow Optimization based Functional Link Artificial Neural Network (BWO-FLANN) model. Also, a novel Non-dominated Sorting Multi-Objective Teaching Learning Based Optimization (NS-MOTLBO) has been proposed for obtaining the solution to Economic Emission Load Dispatch (EELD) in a combined operation of the grid with solar photovoltaic source by considering the future predicted load. The EELD is an inherently multi-objective problem with nonlinear constraints, such as the generator power limits, power balance criteria, transmission line capacity, prohibited operating zones, etc., that make it more complex, causing extra computational burden and convergence issues. An effective constraint-handling methodology is also used in this paper to achieve the lowest possible constraint violation. The proposed approach has been implemented in two test situations, each with distinct solar radiation. The Pareto optimal fronts for various hours were obtained, indicating possible scheduling of the corresponding periods. Non-parametric statistical testing is carried out to investigate the dominance of our proposed approach compared to the other state-of-the-art prediction models. [ABSTRACT FROM AUTHOR]

• A new passivity enforcement approach with complete formulation. • Passivity enforcement in wideband line and cable models. • First demonstration of combined perturbation of residues. • Superior performance in passivity enforcement compared to existing approaches. • Formulation resulting in minimum perturbation. Passive component models are necessary to ensure numerical stability in the simulation of electromagnetic transients in power systems. However, it is challenging to represent transmission lines and cables with frequency-dependent wideband models that are accurate, efficient, and passive. This paper proposes a new method for the passivity enforcement of wideband line and cable models. The wideband models rely on pole-residue identification of characteristic admittance and propagation function in rational forms. In case the resulting models are not passive, the proposed method simultaneously applies perturbation to the residue matrices of characteristic admittance and propagation function. The set of equations related to passivity enforcement through the residues of propagation function in phase domain is complex and presented for the first time in this paper. The proposed approach minimizes the overall perturbation for maintaining passivity as opposed to the existing simplified approaches that rely on the perturbation of the residues of either characteristic admittance or diagonal elements of propagation function. The performance of the method is validated with application cases, and it is shown that it outperforms the existing methods that seek simplification in problem formulation. [ABSTRACT FROM AUTHOR]

• A model for spatial reliability of power transmission lines is presented. • Authors prove the existence of the correlation between outages in the power grid and geographical position of lines. • More accurate predictions were obtained by the proposed model as compared to the Poisson and Poisson hierarchical models. The paper is devoted for the problem of assessment of the dependence of power transmission lines outages on the geographical position in the network. Authors present the model based on Poisson–gamma random field for the purpose of capturing the information about the strength of correlation between the power transmission network outages and geographical positions. The model presentation is followed by the analysis of the model and application to the North American power grid. The main finding is that outages of the power grid are geographically correlated and this effect should be incorporated into the overall reliability assessment of the grid to obtain more accurate estimates. It is proved in this paper, that taking into account dependency of line outages on the geographical location, enables to obtain more accurate results as compared to classical Poisson and to hierarchical Poisson–Bayesian models. [ABSTRACT FROM AUTHOR]

Highlights • Correlation of uncertainties in wind energy and load profiles from field records. • Optimal power flow with dynamic thermal rating for day-ahead planning. • Combining affine arithmetic and probabilistic (Monte Carlo) methods. • Identification of low-risk wind curtailment strategies for wind integration. Abstract Large-scale integration of variable and unpredictable renewable-based generation systems poses significant challenges to the secure and reliable operation of transmission networks. Application of dynamic thermal rating (DTR) allows for a higher utilisation of transmission lines and effectively avoids high-cost upgrading and/or reinforcing of transmission system infrastructure. In order to efficiently handle ranges of uncertainties introduced by the variations of both wind energy sources and system loads, this paper introduces a novel optimization model, which combines affine arithmetic (AA) and probabilistic optimal power flow (P-OPF) for DTR-based analysis of transmission networks. The proposed method allows for the improved analysis of underlying uncertainties on the supply, transmission and demand sides, which are expressed in the form of probability distributions (e.g. for wind speeds, wind directions, wind power generation and demand variations) and related interval values. The paper presents a combined AA-P-OPF method, which can provide important information to transmission system operators for evaluating the trade-off between security and costs at a planning stage, as well as for selecting optimal controls at operational stage. The AA-P-OPF methodology is illustrated for a day-ahead planning, using a case study of a real transmission network and a medium size test distribution network. [ABSTRACT FROM AUTHOR]

Highlights • A novel piecewise linear loss model is proposed for accurate DCOPF calculation. • Loss parameters are statically evaluated to maintain FTR compatibility. • A weighted integral error minimisation is performed with suitable weight function. • The weight term is varied depending upon the high or low line loading condition. • A general solution technique for the proposed error minimisation is developed. Abstract The objective of this paper is to explore a better curve fitting technique that can improve the power flow accuracy of the piecewise linear loss modelling in the DC optimal power flow (DCOPF) calculation. The refinement of the DCOPF model is carried out in view of a power market that employs the locational marginal pricing principle for market clearing, performs multiple settlements and issues financial transmission rights. The piecewise linear loss modelling exhibits a typical advantage over the conventional purely linearised loss modelling in terms of the risk hedging capability of financial transmission rights. Unlike the available piecewise linear loss models with static parameters, the static curve fitting technique proposed in this paper evaluates loss parameters by means of some weighted error minimisation based upon a binary classification of the line loading level. Detailed mathematical procedure is developed to obtain the solution of the proposed curve fitting optimisation problem. The power flow accuracies of different linear and piecewise linear loss models that are suitable for the specified market framework are assessed and compared. Extensive case studies are performed on a 118-bus, a 1354-bus, and a 2383-bus systems to justify the merit of the proposed piecewise linear loss modelling technique. [ABSTRACT FROM AUTHOR]