Search

This paper deals with the lightning protection of 110 kV substation at the wind park Ivan Sedlo against transients caused by direct lightning strikes into connected 110 kV overhead line. Lightning protection level (LPL) I as per standard IEC 62305-1 is selected for this substation to reduce probability of equipment failure to low level. Calculations are done in the EMTP-ATP software. Three critical scenarios are analysed: shielding failure at the connected 110 kV overhead line, lightning strike to the top of first tower in front of the substation and lightning strike to the top of gantry tower at the entrance to the substation. It is presented that LPL I for analysed configuration of substation can be achieved by installing two sets of surge arresters. First set of surge arresters is installed in the transmission line bay, while second set of surge arresters is installed in the transformer bay. Transferred lightning transients through the power transformer are also calculated. It is presented that one additional set of surge arresters is necessary at the 30 kV side of the power transformer, to protected it against transferred lightning transients. Energy duty of all three sets of surge arresters is calculated. At the 110 kV voltage level energy stress of surge arresters is significant and strongly depends on the substation grounding resistance value. Estimated energy stress of set of surge arresters at the 30 kV voltage level is very low. [ABSTRACT FROM AUTHOR]

Phase-to-ground discharge of transmission lines due to ice cover is a common issue. To assess the risk of phase-to-ground discharge of overhead lines under complex ice-covering conditions, this study used finite element analysis to model the interaction between ground wire, conductor, and insulator. The study examined how different factors affect the minimum safe distance between the conductor and ground wire, as well as the risk coefficient of phase-to-ground discharge and the risk zone. The finding reveals that as icing thickness increases, conductor bouncing intensifies, reducing the phase-to-ground distance, and placing one half of the line span within the risk zone for the given conditions. For the same length of de-icing, the closer the de-icing region is to the midpoint, the greater is the maximum jump height of the conductor. When the span is extended to 600 m, the risk range covers approximately 70% of the total line length. Under strong winds, conductor lateral displacement increases with wind speed, which leads to a higher risk of discharge. [ABSTRACT FROM AUTHOR]

Copyright of Przegląd Elektrotechniczny is the property of Przeglad Elektrotechniczny and its content may not be copied or emailed to multiple sites or posted to a listserv without the copyright holder's express written permission. However, users may print, download, or email articles for individual use. This abstract may be abridged. No warranty is given about the accuracy of the copy. Users should refer to the original published version of the material for the full abstract. (Copyright applies to all Abstracts.)

The negative influence of single-phase-to-ground faults in networks with an isolated neutral, resulting from a breakdown of pin insulation, is analyzed. A concept for early detection of damage to pin insulators is proposed, based on measuring changes in leakage current through the insulators caused by changes in the capacitance of the “pininsulator-wire” system. For this purpose, a simulation of the system was done. A model of the geometric dimensions of the insulator is created with taking into account the design features of the installation of the line wire in the AutoCAD software package and the distribution of the electric field is simulated in the Comsol Multiphysics 5.6 package, which makes it possible to estimate the electrical capacitance. The dependence of the calculated electrical capacitance of ShF-20G insulators on the dielectric constant, diameters and grades of wires used on 6-10 kV overhead power lines and options for wire bundles is considered. Numerical values of the capacitance of the “pin-insulator-wire” system were obtained for different configuration options. It has been shown that the state of the insulator material has a decisive influence on the capacity of the system. References 11, figures 2, tables 2. [ABSTRACT FROM AUTHOR]

This article covers the analysis of voltages induced on the conductors of a de-energized circuit of a multi-circuit, multi-voltage HVAC transmission line. As a result of the multiplied interactions between the circuits in such lines, the expected electrical shock currents (touch currents) to which a lineman performing live work on such a line may be exposed are determined. A number of supporting structures of three- and four-circuit lines with various degrees of geometric asymmetry are analyzed. Analyses have shown that in multi-circuit lines in which circuits of different voltages are carried on a common structure, despite the outage of one of the circuits, touch voltages and electrical shock currents (touch currents) exceeding the permissible values can be expected on its conductors, endangering the safety of the lineman. The arrangements of s in such lines that provide the smallest values of touch currents are indicated. [ABSTRACT FROM AUTHOR]

This article presents a solution to mitigate the switching overvoltage for the 220 kV overhead line and substation. This article presents the results of the EMTP simulation of the switching overvoltage phenomenon on the substation and the 220 kV overhead line connecting from Ban Ve hydroelectric plant through Do Luong substation to Hung Dong substation. The main causes leading to switching overvoltage due to switching on the 220 kV overhead line without loads, closing capacitors and closing on transformers are investigated and simulated to evaluate these effects on the operation of the power system. In instances where serious switching overvoltage occurs, the author suggests solutions for mitigation. These solutions are verified through simulation using EMTP software. The simulated results presented clearly show that, the proposed solution can reduce the peak values of switching overvoltages with reasonable accuracy. [ABSTRACT FROM AUTHOR]

Copyright of Scientific Papers of Electrical & Control Engineering Faculty Technical University of Gdansk / Zeszyty Naukowe Wydzialu Elektrotechniki & Automatyki Politechniki Gdanskiej is the property of Gdansk University of Technology, Faculty of Electrical & Control Engineering and its content may not be copied or emailed to multiple sites or posted to a listserv without the copyright holder's express written permission. However, users may print, download, or email articles for individual use. This abstract may be abridged. No warranty is given about the accuracy of the copy. Users should refer to the original published version of the material for the full abstract. (Copyright applies to all Abstracts.)

Simple Summary: Bird mortality resulting from collisions and electrocutions with overhead lines (such as power lines and phone lines) has contributed to the decline of various avian species globally. Specifically, overhead line collisions pose a significant threat to the conservation of the Canarian houbara bustard (Chlamydotis undulata fuertaventurae), an endangered subspecies endemic to the Canary Islands. This study focuses on postmortem findings from Canarian houbara bustards that collided with overhead lines. We describe the necropsy findings of Canarian houbara bustards found dead near overhead lines, and we investigated, using a forensic approach, whether the animal survived the initial trauma. The mortality of birds resulting from collisions and electrocutions with overhead lines, such as power lines and phone lines, among others, has been implicated in the decline of various avian species globally. Specifically, overhead line collisions pose a significant threat to the conservation of the Canarian houbara bustard (Chlamydotis undulata fuertaventurae), an endangered subspecies endemic to the Canary Islands. This study centers on the postmortem findings of Canarian houbara bustards that have collided with overhead lines, providing insights into the post-collision outcomes for these birds. A complete standardized necropsy of nine Canarian houbara bustards revealed that trauma was the cause of death in all cases. The most notable gross lesions associated with trauma included bone fractures, soft tissue lacerations, hemorrhages, luxations, and hemocoelom. The inguinal area, chest, and wings were the body regions more frequently affected. A histopathology, immunohistochemistry, and entomology analysis confirmed that numerous birds survived the initial trauma. We concluded that when a houbara bustard collides with an overhead line, it frequently survives the initial trauma, with a survival time ranging from minutes to hours. The histopathology, immunohistochemistry, or entomologic analysis may be helpful to approximate the timing interval between trauma and death. [ABSTRACT FROM AUTHOR]

The means for calculation and selection of phase-differential protection settings of overhead lines of L60 microprocessor protections of the General Electric company in complex electrical networks up to 10,000 nodes was developed. This software allows to select settings according to the possible types of mixed signals: forward-sequenced and reverse-sequenced, as well as additional criteria. The program makes it possible to check the sensitivity of the starting and disconnecting devices in the case of symmetrical and asymmetrical short circuits, in the case of maximum reverse power flows in various mixed starts. Ref. 3 fig. 5.

In order to adjust the electric power network to today's trends—such as the charging of electric vehicles, design of the Internal Electricity Market (IEM), headway of renewable energy sources, etc.—the demand for flexible network solutions is increasingly significant. Dynamic line rating (DLR) technology offers a flexible solution for the uprating of overhead lines. Moreover, the DLR methodology can be used in a wider system approach in order to establish a line management system, including functions such as ice prevention subsystems or the real-time tracking of clearances. Therefore, the extension possibilities and operational features of DLR-based systems have been extensively researched in the last few years, which is also confirmed by the high number of pilot projects funded for research and development on the topic of DLR. The key question during the implementation of a DLR system is the obtainable operational safety of such a system. This mainly depends on the installation places of the field equipment and the accuracy of the line rating calculation models. The aim of this article is the comparison of the so far available international line rating calculation models and also to propose another way for the determination of the real-time line rating. Moreover, laboratory measurements and case studies are presented for the confirmation of the proposed model's reliability. [ABSTRACT FROM AUTHOR]

As global electricity demand continues to rise, innovative transmission line designs are being developed to enhance efficiency and reliability. Recent studies emphasize the urgent need for advanced structures that improve transmission capabilities. In this context, optimally designed unconventional lines with higher natural power emerge as potential game changers. Various electrical, mechanical, and structural aspects must be studied for a new overhead line design. Among them, evaluating these new transmission line designs against established safety standards is crucial, particularly concerning low-frequency (50 or 60 Hz) electric fields generated under these new lines. This paper comprehensively analyzes the electric fields generated by conventional and unconventional overhead transmission lines. By calculating the electric field for each sub-conductor individually, we offer a detailed comparison highlighting the differences in field distribution between these two line types. Our findings indicate that the unconventional transmission lines exhibit a more favorable electric field profile and comply with current exposure limits set by regulatory agencies. This research underscores the potential of unconventional designs to improve safety and minimize environmental impact while addressing the challenges posed by increasing electricity demands.

One of the key goals in the overhead power lines at the isolated neutral system 6–10–35 kV is topographic search area limitation for a single phase-to-ground (SPG) fault. This will ensure reliability improvement warranty and continuity of power supply. No fault founded in time can lead to failure of electrical equipment. Faults can initiate a ground fire in dry-weather period, which requires preventive shutdown of power lines with subsequent economic damage to power supply organizations. The paper proposes the use of emergency mode parameters, namely, zero-sequence voltages, in order to determine the faults locations in a calculated way. The need for additional installation of measuring voltage transformers at terminal substations is associated with some financial costs. In this regard, the possibility of their limited use is being considered. It has been shown that in this case the emergency section can be localized with accuracy down to the tap if there are no measuring voltage transformers on it. To calculate the SPG location, a mathematical model of lines with distributed parameters has been used. Signals at higher harmonics (HH) generated in the electrical network by arc faults, are considered useful. Full-scale experiments show the HH presence also during electrical contacts of wires with metal structures. The high frequency of the signal causes a significant change in voltage along the length of the line, which increases the accuracy of calculations. The use of zero sequence voltages promotes detuning from the influence of substation load. An algorithm has been developed for performing calculations to determine the location/area with a ground protection zone on a tree-structure feeder.

Phase-to-ground discharge of transmission lines due to ice cover is a common issue. To assess the risk of phase-to-ground discharge of overhead lines under complex ice-covering conditions, this study used finite element analysis to model the interaction between ground wire, conductor, and insulator. The study examined how different factors affect the minimum safe distance between the conductor and ground wire, as well as the risk coefficient of phase-to-ground discharge and the risk zone. The finding reveals that as icing thickness increases, conductor bouncing intensifies, reducing the phase-to-ground distance, and placing one half of the line span within the risk zone for the given conditions. For the same length of de-icing, the closer the de-icing region is to the midpoint, the greater is the maximum jump height of the conductor. When the span is extended to 600 m, the risk range covers approximately 70% of the total line length. Under strong winds, conductor lateral displacement increases with wind speed, which leads to a higher risk of discharge.

The development of overhead lines has met the electricity demand of the rapidly developing society. However, the large-scale installation of overhead lines and the natural environmental differences in different regions increase the complexity of the real-time management of the lines. To improve the efficiency of line management, this article constructs a theoretical and simplified electromagnetic field model of 500 kV three-phase overhead lines and studies the method of monitoring the current-sag state of the lines based on analyzing the distribution of magnetic field intensity under the three-phase overhead lines. Moreover, the placement of the tunneling magnetoresistance (TMR) sensor array was analyzed, and the current and sag reconstruction algorithm of the line was further proposed. The calculation results show that the simplified magnetic field model is accurate in most areas under the overhead line. The comparison of condition number and sensor position sensitivity value on sensor placement evaluation shows that the sensor position sensitivity value is more comprehensive, and it is recommended to use dual-axis TMR magnetic sensors. The relative error of the line sag calculated by the proposed TMR sensor array and algorithm is less than 3% and 4% for balanced and unbalanced three-phase line currents, respectively.

Measurements of active power losses to corona in overhead transmission lines of ultrahigh voltage have established that these losses are a function of voltage (fourth to eighth) degree. A methodology, algorithm, and software implementation for modeling an active power losses to corona as a voltage function are proposed, taking into account the voltage distribution along the line. A program has been developed in the form of a computational module based on a long-line equation. Active power losses to corona are taken into account in the form of nonlinear conductivity. The program can be used to simulate steady-state conditions of AC overhead lines, as well as in design, analysis of optimal operating modes, and comparative analysis of the accuracy of simplified models. [ABSTRACT FROM AUTHOR]

In this paper, an efficient closed-form expression for overvoltage of overhead lines under direct strike in the presence of lightning arresters is presented. The lightning arresters are also grounded via two grounding systems namely vertical electrode and horizontal grid. The simulation results based on the exact method show that among different parameters, the resistivity of soil and line height affect the overvoltage. To extract the closed-form expression, adaptive-network-based fuzzy inference systems (ANFIS) are used. In creating the ANFIS-based expression, it is first assumed that the electrical parameters of the soil are constant. Then a number of input-output pairs (inputs are soil resistivity and line height and the output is overvoltage) are computed from exact methods to train the algorithm. Once the algorithm is converged, the efficient expression is extracted. This simple expression can be easily used in dispersive soils (frequency-variant electrical parameters) and horizontally two-layered soils (non-homogenous electrical parameters) provided that the equivalent frequency and equivalent resistivity concepts respectively in dispersive and two-layer soils are used. [ABSTRACT FROM AUTHOR]

The mortality of birds resulting from collisions and electrocutions with overhead lines, such as power lines and phone lines, among others, has been implicated in the decline of various avian species globally. Specifically, overhead line collisions pose a significant threat to the conservation of the Canarian houbara bustard (Chlamydotis undulata fuertaventurae), an endangered subspecies endemic to the Canary Islands. This study centers on the postmortem findings of Canarian houbara bustards that have collided with overhead lines, providing insights into the post-collision outcomes for these birds. A complete standardized necropsy of nine Canarian houbara bustards revealed that trauma was the cause of death in all cases. The most notable gross lesions associated with trauma included bone fractures, soft tissue lacerations, hemorrhages, luxations, and hemocoelom. The inguinal area, chest, and wings were the body regions more frequently affected. A histopathology, immunohistochemistry, and entomology analysis confirmed that numerous birds survived the initial trauma. We concluded that when a houbara bustard collides with an overhead line, it frequently survives the initial trauma, with a survival time ranging from minutes to hours. The histopathology, immunohistochemistry, or entomologic analysis may be helpful to approximate the timing interval between trauma and death.

To supply stable and high-quality power according to the advancement of industrial growth, electric power companies have performed maintenance of power facilities using various methods. In the case of domestic power distribution facilities, there are limitations in performing diagnostic management on all facilities owing to the large number of facilities; therefore, old facilities are managed using the health index assessment method. The health index assessment comprises only facility operation data and external environmental data and is managed only for four types of distribution facilities including overhead/underground transformers and switchgears. In the case of high voltage overhead lines, there are a large number of wires such as transformers and switchgears connected to the lines, and the ripple effect of power outages is large. However, in Korea, there is no overhead line health index standard. In overseas cases, a health index for overhead lines was developed, but only the material characteristics and surrounding environment of the overhead lines were considered and economic feasibility was not considered. Therefore, in this paper, we developed a health index evaluation methodology for ultra-high voltage overhead lines that considers economic feasibility. In this paper, unlike the existing health index evaluation method that uses only operational data and external environmental data to determine facility performance evaluation and aging replacement standards, we developed an economic health index evaluation methodology that additionally considers failure probability and risk costs. Using the health index assessment methodology developed in this paper, it is possible to expect a reduction in facility operating costs and investment costs from the perspective of the electric power companies through the replacement of old extra-high voltage overhead cables. In addition, from the perspective of consumers, it is expected to increase power reliability and reduce the ripple effect of failure by preferentially replacing equipment with a high probability of failure. [ABSTRACT FROM AUTHOR]

With the rapid increase of the use of wind power, the extension of the grid relatively lags. Under this circumstance, the static thermal rating (STR) of the grid-connected line of the wind farm restricts the wind power integration due to its conservative nature, and the security operation issue of the grid-connected lines of wind farms is drawing more and more attention from researchers. Aiming at this issue, a dynamic thermal rating technique (DTR)-based early warning method for the current-carrying security of the gird-connected overhead line is proposed. First, the probabilistic distributions of the micrometeorological elements around the overhead conductor are predicted based on the DTR measurements. Then, the Monte-Carlo simulation method is used to simulate the temperature dynamic distributions of the overhead lines under the results of the probabilistic prediction results, thus providing the probabilistic security early warning according to the temperature violation. The method can exploit the efficacy of the DTR technique, and it is of significance in improving wind power integration and energy saving & emission reduction. Finally, an example is given to verify the effectiveness of the method.

Existing electric-field integral inversion methods have limited field application conditions, and they are difficult to arrange electric-field measurement points on high-span overhead lines. This paper proposes a non-intrusive voltage measurement method for overhead transmission lines based on the near-end electric-field integration method. First, the electric-field distribution under 10 kV lines is calculated by finite element simulation software. The electric-field distribution of the plumb line and the discrete integral node below the wire are analyzed. Then, based on traditional electric-field integration, a line-voltage-inversion measurement method based on near-end electric-field integration is proposed. In addition, a voltage-monitoring system based on near-end electric-field integration is constructed. Next, the numerical integration types, the number of integration nodes, and the scale coefficient of the near-end region of the inversion algorithm are optimized with the electric-field simulation data. Finally, to verify the voltage-inversion method proposed in this paper, a test platform for overhead-line voltage is constructed using a MEMS electric-field sensor. The results indicate that the voltage-inversion error is 5.75%. The research results will provide theoretical guidance for non-intrusive voltage-inversion measurement of overhead lines. [ABSTRACT FROM AUTHOR]

This article justifies the transfer capability of the tuned power transmission of Itat-Chelyabinsk power transmission line, which includes the Itat-Ekibastuz-Chelyabinsk line in the 1150 kV dimensions, which is currently operating at a voltage of500 kV. The stages of operation of tuned power transmission at a voltage of 500 kV and 750 kV are considered taking into account all technical limitations. The analysis made it possible to estimate the transfer capability of the Itat-Ekibastuz-Chelyabinsk overhead transmission line as part of the tuned Itat-Chelyabinsk power transmission line (TPT), and to make a conclusion about the necessity of developing special equipment for the implementation of TPT circuit variants at a voltage of500 kV and 750 kV. The technical requirements for the development of tuning reactors for TPT operation at full transfer capability are defined.

Copyright of Przegląd Elektrotechniczny is the property of Przeglad Elektrotechniczny and its content may not be copied or emailed to multiple sites or posted to a listserv without the copyright holder's express written permission. However, users may print, download, or email articles for individual use. This abstract may be abridged. No warranty is given about the accuracy of the copy. Users should refer to the original published version of the material for the full abstract. (Copyright applies to all Abstracts.)

Accurate short-term prediction of overhead line (OHL) transmission ampacity can directly affect the efficiency of power system operation and planning. Any overestimation of the dynamic thermal line rating (DTLR) can lead to the life-time degradation and failure of OHLs, safety hazards, etc. This paper presents a secure yet sharp probabilistic model for the hour-ahead prediction of the DTLR. The security of the proposed DTLR limits the frequency of DTLR prediction exceeding the actual DTLR. The model is based on an augmented deep learning architecture that makes use of a wide range of predictors, including historical climatology data and latent variables obtained during DTLR calculation. Furthermore, by introducing a customized cost function, the deep neural network is trained to consider the DTLR security based on the required probability of exceedance while minimizing the deviations of the predicted DTLRs from the actual values. The proposed probabilistic DTLR is developed and verified using recorded experimental data. The simulation results validate the superiority of the proposed DTLR compared with the state-of-the-art prediction models using well-known evaluation metrics.

Copyright of Electric Power Automation Equipment / Dianli Zidonghua Shebei is the property of Electric Power Automation Equipment Press and its content may not be copied or emailed to multiple sites or posted to a listserv without the copyright holder's express written permission. However, users may print, download, or email articles for individual use. This abstract may be abridged. No warranty is given about the accuracy of the copy. Users should refer to the original published version of the material for the full abstract. (Copyright applies to all Abstracts.)

Copyright of Electric Power Automation Equipment / Dianli Zidonghua Shebei is the property of Electric Power Automation Equipment Press and its content may not be copied or emailed to multiple sites or posted to a listserv without the copyright holder's express written permission. However, users may print, download, or email articles for individual use. This abstract may be abridged. No warranty is given about the accuracy of the copy. Users should refer to the original published version of the material for the full abstract. (Copyright applies to all Abstracts.)

Hybrid high voltage direct current systems utilized for bulk-power transmission have recently attracted more attention. The overhead lines (OHLs) are mainly used for the implementation of such systems due to their outstanding economic advantages. However, OHLs are vulnerable to temporary faults, jeopardizing the safe and reliable operation of the network. The resiliency to the line faults is of considerable significance to the power transmission. This paper proposes a fault property identification strategy based on the Pearson correlation coefficient for the LCC-MMC hybrid HVDC system which can differentiate temporary and permanent faults. To achieve this, a voltage signal is injected into the faulty line by decreasing the firing angles of the LCC-based rectifier. Based on the established OHLs model and the injected signal, an estimated backward travelling wave can be accurately calculated. The fault property is identified by comparing the wave difference of the real backward travelling wave and the estimated backward travelling wave. The proposed strategy has a high accuracy since all influencing factors including the fault resistance, fault distance, and line parameters have been taken into account. Finally, to verify the efficacy of the proposed algorithm, several simulations have been performed using PSCAD/EMTDC. The simulation results show that the proposed algorithm can effectively distinguish the fault property. [ABSTRACT FROM AUTHOR]

Copyright of Przegląd Elektrotechniczny is the property of Przeglad Elektrotechniczny and its content may not be copied or emailed to multiple sites or posted to a listserv without the copyright holder's express written permission. However, users may print, download, or email articles for individual use. This abstract may be abridged. No warranty is given about the accuracy of the copy. Users should refer to the original published version of the material for the full abstract. (Copyright applies to all Abstracts.)

This paper deals with the mitigation of 110 kV double-circuit overhead line magnetic field inside five-story Khrushchev buildings. We show that the magnetic field can exceed the reference level 0.5 μT in 90 % part of living space. To mitigate the magnetic field, we propose the inverted L-shaped grid shield with conductors on the wall and in the attic of the building. Using the analytical model of the grid shield and the numerical simulation, we determine the parameters of the L-shaped grid shield which provides the magnetic field normalization in 97 % part of living space. Further improvement of the grid shield profile, in particular, the placement of some conductors in the basement, allows to reduce the quantity of metal of the shield by 15 % while maintaining the shielding efficiency. Also we consider the magnetic field normalization for the overhead line with a rated current of 500 A. In this case, the quantity of metal of the grid shield increases 2.74 times.

• Overhead line rating forecast helps system operators for making decisions. • Prediction of maximum level of ampacity allow to satisfy safe operating conditions. • Regression machine learning models give an excellent performance. Transmission system operators operate overhead lines in power transmission networks by using thermal ratings calculated under static conditions. These static assumptions sometimes lead a network to work outside the range of safe conditions, and sometimes to work underutilized. For this reason, the use of dynamic ratings, which depend on the meteorological conditions of the region under study and thus are more adaptable and better able to ensure optimal operation, has become common. The main drawbacks of these dynamic rating calculations are that to perform day-ahead network scheduling, the ampacity must be known in advance, and unlike static ratings, dynamic ratings are complex to predict due to their great variability. This work defines a methodology based on machine learning techniques that enables the prediction of the ampacity of overhead transmission lines to facilitate the adjustment and optimization of the amount of energy that can be safely transmitted through a network. The results have been validated with real data gathered by sensors from an overhead line. In conclusion, the safety and working conditions of power lines can be improved by applying the selected models, since the number of periods working out of safe conditions can be reduced approximately from 18 % to 5 %. [ABSTRACT FROM AUTHOR]

Traditional current monitoring devices (e.g. current transformers) for transmission and distribution (T&D) networks are mostly installed at substations, so real-time and accurate information on current is almost unavailable for on-site load current monitoring, imbalance assessment, and equipment maintenance. This increases the fault risk in T&D networks and degrades the reliability and quality of the power supply. To address such a situation, this study proposes an intelligent and contactless current measurement method. The proposed method uses only a small number of magnetic-field sensors and the conductor geometry specification of an overhead line obtained from utilities. The simulation results show that the proposed method can accurately calculate each phase current using only three magnetic field sensors. In addition, a scaled-down overhead line measurement system was built to test the proposed method. The experimental results verify the feasibility of the proposed contactless method for overhead-line current measurement with less than 10% maximum measurement error. [ABSTRACT FROM AUTHOR]

This paper presents an assessment of lightning protection schemes for overhead lines from two aspects: protection performance and economic cost. Considering the random nature of lightning, the Monte-Carlo method with a heuristic technique is applied in the assessment. The one-dimensional finite-difference time-domain method is adopted to evaluate lightning overvoltages on insulators and lightning currents in surge arresters for failure assessment. The failure rate of an overhead line is addressed under both direct lightning and indirect lightning. A reduced set of design parameters are identified. It is found that the line insulation itself with a critical flashover overvoltage of less than 200 kV is not sufficient for lightning protection, especially against direct strokes. With other protection options, however, increasing the insulation level can greatly improve the protection performance. Installing surge arresters on every pole results in the best protection performance, but could be extremely expensive due to the replacement of failed surge arresters. The shielding wire provides moderate protection performance with a relatively low cost. The combination of the shielding wire and surge arresters provides much better performance under a wide range of soil conductivity with a moderate cost. It is worth mentioning that adopting high insulation strength for overhead lines in the new-line design could lead to significant cost savings for lightning protection. Guidelines for selecting design parameter values and protection schemes are provided, as well as a procedure for performance-cost evaluation. [ABSTRACT FROM AUTHOR]

The hybrid dc circuit breaker is one of the most promising dc circuit breakers (DCCBs). However, its cost is relatively high, and the completion of its fault isolation is significantly delayed because of the large current limiting inductors configured in the multiterminal dc grid. Besides, due to the utilization of overhead lines, the probability of temporary faults is much increased, which means there is a great possibility that the power supply can be rapidly restored by reclosing DCCBs. However, the temporary faults must be distinguished from the permanent faults before the reclosing operation to avoid damaging the fragile power electronic equipment. Therefore, considering the above issues, a novel multiport hybrid dc circuit breaker (MHCB) is proposed in this article. The MHCB mainly has three advantages: the reduced implementation cost by sharing the expensive main breaker among multiple lines, the reduced fault isolation time by bypassing the current limiting inductor during energy dissipation, and the ability to reclose softly. Extensive simulations and experiments verify the effectiveness of the device. In addition, the comparison of the new device and existed solutions is presented. [ABSTRACT FROM AUTHOR]

This paper deals with the magnetic field mitigation of 110 kV trefoil single-circuit and double-circuit overhead lines by grid shields. The shields under study are made of aluminum conductors connected in parallel. These shields are mounted on the walls of the building. We study the efficiencies of plane and U-shaped grid shields as the dependence from the quantity of metal. As the result, we show that the plane grid shield does not supply the required efficiency of magnetic field mitigation in corner areas of the building. At the same time, the U-shaped grid shield having equivalent quantity of metal allows to mitigate the magnetic field to the reference level 0.5 µT in more than 97 % part of the building.

Short-term contact losses between a pantograph and a contact wire are not included in the standards nor are they taken into account in evaluating pantograph-contact wire interaction. These contact losses, however, accelerate wear and tear as well as disturb operation of vehicles’ drive systems. The article presents the effects of short-term contact breaks as well as an analysis of impact of contact breakages on a vehicle’s current at 3 kV DC power supply. Results of voltage and current oscillations measured in real conditions when pantograph of a DC driven chopper vehicle was running under isolators were presented. Then a simulation model of a vehicles with ac motors and voltage inverters was derived to undertake simulation experiments verifying operation of such a vehicle in condition similar to those measured in real condition.

Analytical expressions are obtained for determining reactive power at the beginning and at the end of an intersystem overhead line, taking into account the parameters of the magnetization branches of power transformers, which allow one to take into account the intensity of the influence of geomagnetic disturbances on power transmission modes. It is shown that an increase in the intensity of geo-induced currents can completely disrupt the transit of reactive power due to the multiple increase in the magnetization power of power transformers as a result of one-sided saturation of magnetic systems. A numerical example is given illustrating the possibility of terminating the transit of reactive power with sufficiently intense geomagnetic disturbances.

New laboratory-based test equipment is described for controlled arc exposure of short lengths of railway electrification contact wire (100 mm) enabling a rapid and low-cost experimental investigation of electric arc damage due to loss of contact between the pantograph and overhead line. The extreme local heating typical of arc sites is found to locally reduce wire hardness, seeding sites for wear and fatigue crack initiation. Contact loss may be produced by poor dynamic behaviour at the pantograph to overhead line interface, often caused by changes in system stiffness or local misalignment of the overhead line. In this study, arcs were generated with computer control of pull away and approach to the wire to carbon strip contact, with peak currents in the range 100 to 200 A for direct current and ± 200 A for alternating current. Metallurgical and mechanical damage identified is correlated against energy input quantified through voltage and current measurements. Interior void formation within the contact wire and modification of grain size are revealed with optical microscopy, metallography, surface mapping and microhardness tests. Initial tests using the new equipment with two materials show the potential for investigating mitigation of arc damage by changing contact wire composition. [ABSTRACT FROM AUTHOR]

Drone‐supported 3D surveying as a basis for planning of a high voltage overhead line DB Energie GmbH operates the high‐voltage railway power supply system in Germany with a total length of approx. 7700 km and thus ensures the secure energy supply of the electrified line sections in the German rail network. On behalf of DB Energie and as a specialist for planning services for high‐voltage and extra‐high‐voltage overhead lines, the technical centre of Omexom Hochspannung GmbH is taking over the technical and legal planning for the "Rethen substation" project and is using the possibility of drone‐based 3D data collection to create the necessary planning basis. The Rethen substation, located to the south of Hanover, serves as the starting and end point for several traction current lines and is to be reconstructed. This makes it necessary to redesign the line projections. A particular challenge is posed by the various prohibitions on access to private land as well as the influence of electromagnetic fields on the sensitive drone technology. In the course of several measurement flights, a total of 1000 high‐resolution individual photos were taken with the help of a system specially configured for this application and processed into a 3D point cloud with approx. 90 million measurement points by means of photogrammetric evaluation procedures. To validate the accuracy of the measurements, terrestrial verification measurements were carried out at individual locations. [ABSTRACT FROM AUTHOR]

Corona discharge characteristics are measured in a corona cage. The difference is found between the q–u curves under double exponential and damped oscillation surges. The behavior of the minor loops is revealed for the q–u curves under positive and negative damped oscillation surges. An extended improvement is made on the traditional approach for modeling of the q–u curves under damped oscillation surges. The extended approach has the capability of describing the complicated trajectory feature of the minor loops. On the basis of the extended approach, an efficient method is proposed for performing lightning surge analysis of overhead lines considering the corona effect. In the proposed method, an overhead line with corona is divided into a certain number of line segments. Each segment is converted into a circuit unit consisting of a non-linear branch and a linear circuit. With these circuit units connected in sequence, a complete equivalent circuit is constructed for the overhead line with corona. The transient responses can be obtained from the solution to the equivalent circuit. Then, the calculated results are compared with the field test results on a test overhead line. [ABSTRACT FROM AUTHOR]

The high-voltage direct current (HVDC) grid has been recognized as an effective solution for renewable energy integration. Currently, two main development trends for HVDC grids are being studied: a DC breaker based HVDC grid and fault-blocking converter based HVDC grid. Although the former has a perfect performance for fault clearance, its development is still highly constrained by the cost and maturity of DC breakers. The latter can extinguish DC faults by the fault-blocking converters. Without using DC breakers, there is no bottleneck in its technical feasibility. Nevertheless, in fault scenarios, such types of HVDC grids will be blocked at length for air-deionization, which is its main drawback. The aim of this paper is to minimize its power interruption time, by optimizing protection coordination strategies. To cover the most complex cases, the overhead line applications, in which the reclosure actions are required to be implemented, are considered. In this paper, the protection requirements of HVDC grids are first discussed, then the benefits of fault-blocking modular multilevel converters (MMCs) and their fault features are analyzed. Based on this, a control function is designed to reduce the air-deionization time. To minimize the influence of the DC faults, a separation methodology for restarting the system is proposed. The effectiveness of the proposed protection coordination schemes is validated by PSCAD/EMTDC simulations.

The key technologies of ultra-high voltage hybrid LCC-VSC MTDC systems are investigated, focusing on the design of system configurations, converter topologies and the control and protection system. A double converter per pole of VSC connection is proposed along with the design of a 5000 MW VSC valve to develop a ± 800 kV/5000 MW large-capacity power transmission. The hybrid MMC topology capable of clearing the DC faults and the control strategy are developed to effectively improve the reliability in case of overhead line faults. The control and protection system of the LCC-VSC MTDC system is introduced to offer flexible operations under both normal and abnormal conditions, which includes voltage/current margin-based coordination, converter switch-in and switch-out, re-connection and drop-off of a third station. Simulations of an LCC-VSC MTDC system based on the LCC-VSC MTDC project are performed.