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In the usual practice, the evaluation of overvoltages due to direct lightning strikes to overhead power lines is focused on the representation of the effects of the lightning current injection, whilst the effects of the coupling between the conductors and the lightning electromagnetic pulse (LEMP) is disregarded. Motivated by recent results obtained for the case of a medium voltage line configuration with a shield wire, this paper extends the analysis to assess the contribution of the LEMP on the lightning performance of an overhead distribution line with and without periodically grounded wires and surge arresters. Moreover, the paper deals with the LEMP effect on the occurrence probability of flashovers on different phases, which is an important information on the service continuity of networks with isolated or compensated neutral earthing. A validation of the results is obtained by comparing the overvoltages calculated by the electromagnetic transient program including the model of the line illuminated by the LEMP and those obtained by a three-dimensional finite difference time-domain approach.

One of the leading causes of power system outages is lightning surges. A precise calculation of lightning overvoltages across insulators has vital significance for the investigation of lightning outages. This study investigates the impact of different lightning surges for the analysis of transient frequency characteristics of line commutated converter (LCC) based ± 800 kV ultra-high-voltage direct current (UHVDC) converter station by developing a wideband (WB) model of the converter station. The influence of lightning flashover criterion (LFC) of double exponential and Heidler surges methods on insulator/gap for precise lightning withstand level is examined. An analytical comparison for LFC of insulator/gap installed at high altitude transmission lines by incorporating the IEEE volt/time curve, CIGRE leader propagation (LP) and improved LP methods is presented. The proposed WB model explores the novel attributes of high-frequency transfer characteristics and the coupling mechanism of transient frequencies passing through the converter station. Moreover, the effect of internal frequency dependant DC line faults on the WB model is examined. The analysis presented here aims to investigate issues like overvoltage, electromagnetic disturbance prediction, insulation design of the equipment and standardisation of sensitivity issues that are being faced by the present relay protection systems.

Based on a ±10 kV three-terminal MMC-MVDC (medium voltage DC distribution system based on modular multilevel converter) system, in this study, the authors mainly study on the influencing factors and protection schemes of the lightning intruding overvoltage (including direct lightning and back-flashover lightning). Firstly, a lightning intruding overvoltage simulation model of the MMC-MVDC distribution system using overhead lines is established based on the PSCAD/EMTDC program. The influence of steady-state operating voltage and the number of converter stations on the simulation results are simulated and analysed. Meanwhile, the proper simulation modelling method of the lightning intruding overvoltage for multi-terminal MMC-MVDC system is proposed. Secondly, the lightning intruding overvoltage is simulated when the line is struck by the lightning stroke current that occurs once in 20 years and the different lightning protection schemes are proposed. Finally, based on the lightning impulse withstand voltage, lightning trip-out rate and the cost of the protection schemes, the lightning protection schemes in different scenarios are proposed. The simulation results show that if the cost of the system is prioritised, the protection scheme of increasing the number of parallel stacks of the DL arresters can be selected, and if the power supply reliability of the system is prioritised, the protection scheme of installing the overhead ground wire as well as reducing grounding resistance can be selected.

Electric vehicle charging has shifted to higher voltages to achieve higher power for more rapid charging capabilities. This article provides a contactless magnetic plug solution that enables medium-voltage grid connections for electric vehicle charging to achieve 3.5- $\text{kV}_{\rm DC}$ -to-400- $\text{V}_{\rm DC}$ , 150-kW rapid charging capabilities. This novel magnetic plug improves upon existing electric vehicle charging solutions by guaranteeing safe operation and connection through galvanic and physical separation from the medium-voltage side. It achieves this with a gap and barrier in the transformer core. We introduce a unique asymmetry in the core to localize parasitic capacitance, fully separating the medium- and low-voltage regions. This approach eliminates arcing risk and allows rapid charging capabilities to be delivered to the general public. This gapped core constitutes the plug action of our proposed charging system. We present solutions for the unique challenges of this solution through a detailed analysis of the magnetic design. We confirm this analysis in finite-element analysis and experimentation. The solution is verified through a scaled laboratory prototype of 20 kW, 1 $\text{kV}_{\rm DC}$ to 50 $\text{V}_{\rm DC}$ that is representative of the proposed 150-kW design. We demonstrate safe, arc-free, disconnection in included active content, a new solution for high-power electric vehicle rapid charging.

Contactless power transfer (CPT) methods have widely been explored for many applications. An isolated wireless power link enables a touch-safe interface without electrically energized contacts eliminating any arc flash or electrocution hazard. The concept presented here will enable safe medium voltage distribution inside data centers eliminating low voltage distribution with bulky cables bringing voltages larger than 1kV directly to the server rack. This paper proposes high-efficiency single-stage contactless power conversion from medium voltage to low voltage for data center applications. The proposed solution is evaluated using a 10kW design example and verified by experimental tests. A plug-in contactless transformer is developed with customized nanocrystalline cores and 3D printed bobbins to improve the DC-to-DC efficiency and manufacturability. A high efficiency converter is developed to maintain a 48V output voltage with a IOOOV input voltage over a wide load range. The DC-to-DC efficiency and frequency modulation performance are analyzed.

The high voltage overhead power lines are greatly exposed to direct lightning strikes due to their significant height. In the case of direct lightning strikes in line’s elements (towers, active conductors, and ground wires) or even in the near vicinity of the line, dangerous lightning overvoltage could appear, thus conducting to the line’s insulators flashover, which can cause the line’s disconnection. In this context this paper aims to analyze the behavior of several power transmission lines of Romania’s national power system, when struck by lightning, considering the keraunic level of the areas they are passing through.

The insulation of the power transmission system experiences stresses due to power–frequency voltage under normal operating conditions, temporary overvoltages at or near power–frequency and transient overvoltages arising either from switching operations and faults or from lightning discharges. However, in the insulation design of extra-high-voltage and ultra-high-voltage systems, transient overvoltages arising from switching operations and faults become the controlling factor. Insulation failure probability under switching overvoltages is the main impressive concern in the estimation of switching surge flashover rate. In this paper, a practical method is used to estimate the switching surge flashover rate of insulation under switching overvoltages generated during energization, re-energization, fault initiation and fault clearing of an unloaded transmission line, which considers the variable characteristics of the insulation strength of the transmission line according to the switching overvoltage waveshape. The results focus on the comparison between traditional and practical methods which considers the effect of the front time on the first 1200-kV UHVAC transmission line in India.

Surge arrester has been proven to be the most effective application to provide optimum lightning protection for the transmission line. Thus, many works on optimizing lightning protection for transmission line have been conducted since the past. However, works on minimizing double circuit outages and surge arrester physical properties during transient overvoltages are less likely to be found. Therefore, in this work, several surge arrester configurations installed on a 132 kV double circuit transmission line were modelled using EMTP-RV to investigate their capability to withstand current and energy discharged by lightning strokes during back flashover phenomena. These configurations were then compared to determine the most effective protection design based on the actual tripping pattern recorded by the lightning detection system (LDS) in Malaysia. The selection was made by considering arresters’ discharge energy due to variation in tower footing resistance, current magnitude, power frequency voltage, lightning tail time and front time, number of towers and span length. It was found that double circuit transmission line tripping can be completely eliminated by installing surge arresters at each phase conductor of one circuit. The selected arresters configuration provides sufficient lightning protection to the transmission line and complies with the discharge energy capability requirement specified by the utility company in Malaysia, of 5.1 kJ/kV for maximum continuous operating voltage (MCOV).

When one undertakes an arc flash study, one must develop a model based on the power system of interest. The model requires estimates of conductor lengths and other data. To ensure that the arc flash study that one is performing does not underestimate the magnitudes of the short circuit currents present within the power system, and to allow for limitations in the procedure by which one develops the model, typically visual inspection, one must carefully estimate the lengths of conductors. Computing “safety margins” can help to avoid errors, and maintenance switches can address the uncertainties involved. The final solution may be software that permits the percentage estimates for impedance elements to be built into the model for various equipment and used to compute arc flash levels on the secondaries of low-voltage circuit breakers.

Silicon carbide (SiC) technology continues to improve, which has led to SiC MOSFETs capable of operating at medium voltage (MV) levels greater than 1.7 kV. These devices are currently being evaluated for use in next-generation MV power electronics. However, evaluation of prototype power electronic systems at MV incurs additional operator risks compared to evaluation of low voltage (LV) systems below 1.7 kV. Due to these inherent risks, the power electronics community needs to apply precautions similar to those used as standard practice in the power distribution industry. This paper presents a test environment that is designed to support high-fidelity measurements of MV power electronics while ensuring operator safety. This environment features an enclosed safety cage with interlocks and fault detection circuitry that interfaces to the equipment under test (EUT). This paper provides guidance for designing and deploying testing infrastructure for MV power electronics, including analysis of arc flash risk for MVDC power electronics. Current arc flash safety standards, which are geared towards power distribution systems, offer limited instruction for MVDC power electronics.

This paper reports on the propagation of lightning overvoltage in a high-voltage direct current (HVDC) meshed grid. Since several topologies of meshed grids have been elaborated in the last decade, we used a common comprehensive reference test platform. The lightning impulse propagation was investigated with regard to the impact of surge arresters and the polarity of the lightning stroke concerning the DC line polarity (±500 kV). Various scenarios were considered, including a direct lightning strike to the DC+ conductor, to the tower, and to the shielding wire in the middle of the span, including backflash on the insulators. The influence of tower footing impedance on overvoltage levels at various nodes was assessed, depicting the critical value. A description of the models used in the simulations was provided. The main focus of the paper was on the wide-area propagation of the overvoltages in the meshed grid, at distant terminals and inside the feeders. An interesting observation was the effects of lightning at the far end of the analyzed grid, propagating through multiterminal and long-distance connections. The presented analysis, based on an exemplary meshed HVDC grid, underlines the importance of the insulation coordination studies and system security studies with respect to the localization of overvoltage protection systems.

Industrial power systems bring considerable challenges in terms of safety and reliability. As any other power network these type of systems have some specific risks, specially when it concerns to short circuit faults. These faults create a phenomenon called Arc Flash, which in some cases can be extremely hazardous for the system equipment, and also for the personnel. The IEEE 1584–2018 standard currently presents a methodology in the calculation of Arc Flash where the incident energy level is calculated based on the symmetrical rms bolted fault current value. However, the first cycles of the fault current are not symmetrical values. Therefore, it is necessary to analyze what happens if the incident energy is calculated as stated in the IEEE 1584–2018 standard, but using the rms value of the asymmetrical current. This article takes into account the asymmetrical current into Arc Flash estimations. This current value will affect considerably the level of incident energy during a fault, specially for systems with a high X/R ratio. Additionally, this article will show up an analysis to see what happens with Arc Flash levels in industrial power systems using high resistance grounding, and comparing it with solid grounded systems, one of the most common grounding means in industry. As this study means an improvement on the safeness of electric systems, simulations were carried out using IEEE 242 system in order to support the content of this paper.

IEEE 1584–2018 contains a significant update to industry models for predicting the incident energy from arc flash. These models include different box sizes, voltages, and electrode geometries. Predictions from these models are compared to tests on medium-voltage equipment. Equipment includes circuit-breaker cabinets, live-front switches, and live-front transformers. Results show what input assumptions are most applicable for each type of equipment (including vertical and horizontal electrodes). For some equipment, particularly with horizontal electrodes, the 1584–2018 predictions underpredicted measurements of incident energy, so multiplier factors may be needed.

Nowadays the protection of overhead distribution lines from atmospheric events, such as lightning strikes, is crucial and represents one of the most discussed topic in the research on lightning. When we deal with distribution lines, the lightning performance, which involves both direct and indirect events, usually neglects the well-known corona discharge that can occur on the conductors. This aspect can be usually accepted, but, as will be discussed in this paper, it cannot be omitted when we deal with overhead distribution lines with high Critical Flash-over value (CFO) and small diameters. The work focuses also on different configurations regarding different line diameters and air conditions.

Lightning is the most frequent reason for high voltage overhead transmission lines faults. Due to the stochastic nature of lightning, the theoretic approaches for evaluation of the performance of overhead transmission lines are far from complete. The field experiences from the practitioners are of great value in lightning performance researches. This work collected a large dataset of lightning faults happened during 2004-2018 in the 220 kV and above overhead transmission lines in Zhejiang province. The characteristics, like temporal, spatial and double circuits faults, of the lightning faults are analyzed in this work. The mechanisms behind these characteristics are also explained in this work, which hope will be helpful in the future researches in lightning performance of overhead transmission lines.

The behavior of 10 kV SiC MOSFETs during a flashover fault condition is investigated comprehensively. A larger turn-off gate resistance R g,off is recommended for 10 kV SiC MOSFETs without Kelvin source to avoid very asymmetrical gate resistance, while a small R g,off is recommended for 10 kV SiC MOSFETs with Kelvin source. Guidelines regarding gate loop inductance and selecting an external capacitor across gate and source terminal are also provided. 10 kV SiC MOSFETs have much higher energy loss under flashover fault compared to typical short circuit faults. The required response time for short circuit protection to safely clear flashover fault should be at least 350 ns shorter than the response time designed to clear conventional short circuit faults.

Outages due to lightning stroke frequently occur on the overhead transmission line operating under tropical conditions. The high lightning flash density makes a higher probability of having either shielding failure or back flashover at the tower. Therefore, mitigation is necessary. This paper evaluates options to improve the 66 kV tower design against a lightning strike. Provided models evaluate effect of polarity, strike time, and lightning peak currents on the performance of 66 kV overhead transmission lines also two scenarios of improving shielding protection, i.e., by additional ground wire and by elevating the cone top of the tower.

With the continuous development of urban power grids, the application of 20 kV all-cable distribution networks is becoming more and more common. The adoption of cables ensure the reliability of the power supply, but also cause the single-phase grounding capacitor current to easily exceed hundreds of amps, which seriously endangers the safe operation of power distribution equipment. Existing researches are mostly based on theoretical analysis, it is believed that low resistance at the neutral point can reduce the system overvoltage level, however, during actual operation, it is found that the abnormal transient voltage and current of some distribution networks cause frequent tripping of the line, and even the phenomenon that the transient voltage and current of the fault phase increases simultaneously during the transient process is observe. Based on the actual failure of a 20kV distribution network, this paper analyzes the single-phase grounding fault of a large-capacity current system. The simulation method is used to reproduce the transient voltage and current waveforms during the fault, extract the characteristic quantities of the simulated waveforms and compare them with the recorded waveforms. It is found that arc grounding is the cause of the failure of the system. By theoretically calculating the voltage offset of the stable grounding process, it is considered that the offset level and recovery speed of the neutral point voltage during the arc grounding flashover are the decisive factors for the arc grounding overvoltage level. Based on this, the influence of factors such as system scale, neutral resistance and grounding resistance on the transient overvoltage of a small resistance grounding system is studied.

The operating experience of power transmission lines shows that the influence of the continuous current process after cloud-to-ground (C-G) lightning return-stroke on the DC line cannot be ignored. Therefore, the characteristics of the continuous current are analyzed statistically in this paper. The lightning overvoltage simulation model considering the long continuous current is built, and the influence of the long continuing current on the operation characteristic of 500 kV DC transmission line is analyzed by simulation. Simulation results indicate that the long continuous current has less effect on the overvoltage amplitude of the transmission line. But after the lightning causes the insulator flashover, the flashover current of the insulator is increased by about 47% of the continuous current amplitude. When the arrester is in normal operation, the energy absorption is mainly determined by the stage of the return-stroke, and the existence of continuous current has almost no influence. However, when multiple return-strokes cause the arrester to fail, the influence of the continuous current needs to be considered.

When the Ultra High Voltage Direct Current (UHV DC) line is struck by lightning, it may cause the protection action of the DC system. In this paper, a simulation analysis model of the lightning transient process of UHV DC line is established, and the influence of the line arrester and its installation position and quantity on the protection action is systematically studied. The research results show that line arresters can reduce the impact of lightning overvoltage on UHV DC system protection and prevent lightning strikes from causing DC system protection under certain conditions. The more line arresters are installed along the line, the more significant the effect.

This paper describes a new procedure and test apparatus that accurately calculates the short-circuit resistance and inductance to the energized bus where measurements are taken. The calculated impedance can be used to predict the available bus fault current to properly size protection devices and inform of arc flash hazards. The calculated impedance can also be used to determine power factor settings to reduce adverse voltage impacts from distributed energy resources such as photovoltaics. The novelty of this apparatus is that it uses a diode-bridge rectifier load that draws less than 0.5% of the available bus fault current to make the required measurements. The apparatus is tested and validated on 120Vac and 277Vac circuits at the Electric Power Research Institute (EPRI) in Knoxville, TN.

Arc flash is one of two hazards primarily associated with electrical systems. Due to its prevalence, the majority of arc flash research has been dedicated to alternating current (AC) electrical systems. However, direct current (DC) electrical systems are becoming increasingly common, such as electrical storage systems (ESSs), solar photovoltaic (PV) panels, and high-voltage (HV) DC transmission lines. Thus, more research is needed to address the arc flash hazards posed by DC electrical systems. Current DC arc flash models are theoretical and lack empirical data compared with AC arc flash models. This paper presents models developed through empirical testing utilizing low-voltage (LV) station batteries. Furthermore, this paper investigates possible interactions between DC arc flash within LV battery systems and atmospheric conditions, such as temperature and relative humidity. Lastly, the paper provides information regarding the implementation of these models within American Electric Power’s (AEP’s) safety practices regarding batteries and DC panelboards.

As the ultrahigh-voltage (UHV) projects are rapidly developing, it is necessary to investigate the problems involved in overvoltage and insulation, thereby providing a technical basis for future UHV projects. The switching overvoltage of closing no-load lines was simulated and analyzed here using two kinds of typical UHV network structures: the power plant to the grid system and the grid-to-grid system. Different factors, such as line length, mode of operation on the power plant side, and short-circuit capacity, are considered. It is possible for lines shorter than 60 km to eliminate the closing resistor, determined by calculating the probability of flashover. We analyzed the phase selection closing in depth to inhibit the switching overvoltage and considered the factors such as phase deviation and the length of the line. Finally, the applicability of phase selection closing is put forward for lines of different lengths.

This paper will propose methods for applying the standard equations of IEEE1584-2018 to address the issues of current limitation, the single pole nature of fuses, and current imbalance not covered by these equations. The goal is to use typical fuse data such as total clearing curves and let-through current data in equations developed for prediction of arc flash hazards. This approach yields calculations consistent with the results of lab tests using current limiting fuses.

Based on completely mastering ±800 kV transmission technologies, the first ±1100 kV direct current (DC) transmission demonstration project is being constructed in China. Combining theoretical analysis and a large number of experiments, the margin of switching overvoltage in converter stations, the configuration scheme and performance of lightning arresters, the shielding angles of ground lines under different geographical conditions, and the maximum air gap of lines have been determined. The switching impulse flashover characteristics of equipotential sphere and typical rod-plane air gaps are also provided. The external insulation is designed differently for light, medium, and heavy pollution areas. For the ±1100 kV project, if the 8 × 1250 mm^2 conductors are applied, the pole gap is 26 m and the height of the line is 25 m, all the electromagnetic parameters will meet the requirement of international electromagnetic standards. The key design points of ±1100 kV converter transformers, smoothing reactors, converter valves, and wall bushings are researched and the 75 mH smoothing reactors, ±1100 kV/5000 A converter valves, and ±1100 kV/5523 A wall bushings are successfully made. The optimised hierarchical connection modes and coordination control measure of the ±1100 kV project are studied and the results can provide sufficient technical support for the demonstration project.

This paper is based on a tutorial presented by the author as a part of the Minicourse on charged particle beams and high-powered pulsed sources given at the 2017 International Conference on Plasma Sciences at Atlantic City, NJ, USA. It is intended to provide a brief overview of the phenomenology and physics of the vacuum surface flashover process. These mechanisms will be used to motivate techniques commonly employed to improve the voltage standoff of insulators. In addition to serving as the primary limiting mechanism for vacuum insulators, vacuum surface flashover has a number of beneficial applications, primarily due to its ability to provide a simple pulsed plasma source, and a number of these applications will be discussed.

In this paper, we simulated transient voltages across insulators and back-flashover at the transmission line tower struck by lightning in the presence of corona on the ground wires. The FDTD method and simplified (engineering) model of corona discharge were used. Three two-circuit 60-m high towers, separated by 400 m, with two overhead ground wires, and six phase conductors (two three-phase circuits) were considered. Back-flashover was assumed to occur at the upper, middle, or lower phase. Operating voltages of phase conductors were modeled by using a voltage source inserted between each phase conductor and ground. It is observed that ground-wire corona serves to reduce voltage peaks and delay the occurrence of flashover. For the upper-phase back-flashover due to a positive 50-kA stroke, the peak voltages across the upper-, middle-, and lower-phase insulators are reduced by 11%, 12%, and 12% by the ground-wire corona, and for a negative 50-kA stroke they are reduced by 8%, 9%, and 9%. Influences of ground-wire corona on transient voltages were also studied for the back-flashover at the middle or lower phase. Presence of operating voltages can lead to either increase or decrease of the peak of transient voltage, with the change being less than 20%. To the best of our knowledge, this is the first FDTD simulation of back-flashover at a transmission-line tower considering both ground-wire corona and operating voltages.

Arc Flash in low voltage equipment (480 volts and below) is a safety issue that can impact work practices for electrical workers. When estimating incident energy for low voltage equipment, the duration of the arc is typically the driving factor. This paper summarizes previous testing results that establish arc sustainability for various equipment configurations, when trip devices do not operate. In some cases, arc duration is limited by the physical conditions of the enclosure and by the driving voltage and current available. Using the maximum duration for arc sustainability can provide more realistic estimated incident energies than using the two-second self-extraction time cited in IEEE 1584-2002. Consequently, required levels of personal protective equipment can be reduced while still providing adequate protection to the worker.

Arc resistant low/medium voltage switchgear and motor controls continue to provide proven levels of additional personnel safety in most every petroleum and chemical facility. The Institute of Electrical and Electronics Engineers (IEEE) and International Electrotechnical Commission (IEC) generated testing guides and standards for these products which are open to some level of interpretation when applied to products other than traditional medium voltage circuit breaker or fundamental motor controller structures for which the current available standards and guides were intended when they were initially written. All medium voltage variable frequency drives, because of their inherent designs, require high volumes of cooling air which pose a real challenge in regards to providing full arc resistant capabilities and compliance to the present testing guides, procedures, and standards. This paper will deliver real solutions to this problem through the application of unique cooling processes, arc channeling technologies, structural enhancements, arc fault energy limiting methodologies and special application considerations when applying arc resistant medium voltage drives.

The lightning strokes can be very harmfull to the high voltage transmission lines especially in case polluted insulator string. In this paper, the lightning overvoltage in the El-Kuorimate - Cairo 500-kV transmission line single circuit is discussed. The leakage current and its harmonic spectrum on clean and polluted 500-kV string insulators are determined under normal condition and lightning strokes. Furthermore, the relation between back flashover and insulator surface condition are discussed under different magnitude of lightning strokes. The results show that the leakage current, thermal losses magnitudes in case polluted insulator are higher than in case clean insulator by about 97.2%. For polluted insulator, less lightning strokes peak will increase leakage current to above 60 mA, and lead to serious insulator flashover faster than clean insulator. This study based on an equivalent electrical model by using Alternative Transients Program (ATP-EMTP) software.

In order to solve the frequently occurring lightning flashover problems on ±500 kV dc transmission lines in China, the authors have conducted the research on the dc line arrester since 2011. In this paper, the structure and installation, technical parameters, and protection performances, as well as their deterministic processes of the arrester are presented and analyzed in detail. In 2013, the authors successfully developed the arrester products, and the type tests show that they have excellent performance parameters and can act effectively against the lightning impulse and cutoff the dc follow current. By now more than 500 dc line arresters have been installed and used on seven ±500 kV dc transmission lines in eight provinces of China. About four years of operating experience shows that the arresters work safely and reliably over a long period of time, and have been effectively reducing the lightning flashover rate of the ±500 kV dc lines.

The paper deals with the response of distribution networks to direct and indirect lightning. The response of the network is analyzed with the aim of inferring the mean time between failures of the connected transformers. This is accomplished taking into account the voltage at the utility frequency, the flashovers occurrence in the line insulators, the location of surge arresters, and the shielding provided by nearby buildings. Two different transformer failure criteria are assumed: a critical value and a disruptive effect model. The results make reference to multi-conductor overhead systems with two different topologies: simple straight line and a real feeder with laterals. It is shown that such a detailed lightning performance analysis is useful in order to select the most appropriate strategy for the installation of surge arresters, which may allow the achievement of the desired mean time between failures at affordable costs.

The study presents novel solutions and risk mitigation strategies to reduce internal arc and accidental electrical contact injuries hazard and health consequences. Motorised closed-door racking in–out operational mode enables to modernise the installed base equipment and to keep personnel at a safe distance: by an innovative hard-bus retrofill design concept, enabling to install a standard motorised-racking withdrawable new breaker into a wide range of existing panels, or by adding on existing panels an external motorisation system applicable to roll-in retrofit. Both solutions improve operational procedure safety on installed base, keeping personnel out of arc flash boundaries and reducing personal protection equipment requirements.

Accelerated aging experimental investigations are performed on polymeric insulators which are used for extra high voltage (EHV) and ultra high voltage (UHV) transmission. A newly developed rotating wheel and dip test facility as per std. IEC 62217 is used for the study. The experimental study is conducted with AC stress for 15000 cycles. The specimen insulators used are of 725 mm creepage and treated under different environmental stresses close to the real service life. The present study focuses on the effect of acidic environment during acid rain encountered by the polymeric insulators. The contaminants used for the study are as per standard and practically observed acid rain information. A comparative study is carried out for normal and acidic environmental conditions, some interesting results are observed. Leakage current monitoring and visual observation were conducted at regular intervals. Results show acid treatment is found to be comparatively more severe than the normal treatment. Further Physicochemical investigation are carried out using Fourier Transform Infrared (FTIR) Spectroscopy and Scanning Electron Microscopy (SEM), Energy dispersive X-ray Analysis (EDAX) and Thermo-Gravimetric Analysis (TGA) which confirm the severity of material degradation of polymeric insulators and corrosion over metal end fittings under acidic environmental condition. (C) 2017 Elsevier Ltd. All rights reserved.

To understand the flashover of roof insulators in high-speed airflows, the breakdown characteristics and mechanisms of a short needle–plate air gap are investigated. An interesting and important phenomenon is found based on an artificial wind tunnel: the breakdown voltage first increases and then decreases. An experiential formula is established to describe the relationship among the airflow velocity, gap distance, and breakdown voltage. A good consistency with the experimental results is obtained. Furthermore, the breakdown mechanisms of the air gap in high-speed airflows are proposed, and the phenomenon is explained and verified according to the theories of gas discharge and fluid dynamics. The airflow blowing effect, which includes the deflection effect and blown away effect, and the airflow density effect are proposed as two dominant factors that affect the breakdown process of the air gap in high-speed airflows. The variation trend of the breakdown voltage with the airflow velocity is predicted. Two extreme points are expected during the variation process; i.e., the breakdown voltage has a maximum and a minimum, to which more attention should be paid. This paper is helpful for the safety operation of roof insulators on the high-speed train.

The Mitigation of arc-flash incident energy is important to increase safety. One method is to reduce the duration of the arc flash by using protective relays to sense an arc-flash fault. This method requires a supply-side switching device that will respond to the protective relaying fast enough to mitigate the incident energy. In many existing installations, medium-voltage (MV) controllable fuses are already installed to provide transformer protection. Before the development of an MV-controllable fuse, the MV fuse would have to be replaced with an MV circuit breaker or circuit switcher to have relay control of the MV protective device. This replacement would have significant equipment and construction costs and require extensive equipment outage time. The MV-controllable-fuse method uses the existing fusegear protecting the primary side of the transformer. The protective relay senses the arc fault and signals the controllable fuse to change to a fasteracting time-current response. The incident energies can be reduced from 200 cal/cm2 to lower than 8 cal/cm2 on the secondary side of the transformer. This article reviews an installation using an MV-controllable fuse to mitigate the incident energy on the equipment connected to the secondary side of the transformer.

This paper describes observation of lightning overvoltages in a 500 kV switching station at Kansai Electric Power Co., Japan. Three types of lightning overvoltages, such as back flashover, direct lightning hit to a phase conductor, and lightning-induced voltage have been observed. The lightning overvoltages due to a back flashover were lower than operation voltage of a surge arrester. The observation suggests that induced voltage caused by electromagnetic fields radiated from a lightning channel affects lightning overvoltages in a station.

This study focuses on the relationship between test current waveforms and impulse withstand capability of metal–oxide varistors (MOVs) (withstand energy, current density, and the number of withstand shots) in repetitive impulse application and discusses the mechanical and electrical failure mechanisms. The performance and relationship of withstand energy and withstand shots for conventional 2-ms rectangular waveform, 4/10- $\mu $ s, and newly introduced 10/350- $\mu $ s impulses are investigated. Notably, the 10/350- $\mu $ s waveform has aspects of both steep rise impulse and long duration impulse. In addition, the varistor voltage change after repetitive impulse applications for 10/350- $\mu $ s and 4/10- $\mu $ s waveforms is investigated. There is no direct relationship between varistor voltage drop and repetitive withstand shots. However, ${V}_{1\ {\rm mA}}$ and ${V}_{0.01\ {\rm mA}}$ changes indicate the degree of MOV damage caused by the impulses and are important factors to monitor progressive damage. Based on these findings, optimal MOV design is discussed.

This paper investigates the influence of structure on the failure of full-scale metal–oxide arresters under successive lightning impulses. Typical structures of arresters are compared by simulation and experiment. With a finite-element model for the electrical-thermal multiple-field analysis, the thermal characteristics of typical structures of full-scale arresters under successive impulses are obtained. It is revealed that the filled solid insulation can contribute to more radial heat dissipation than filled gas. Experimentally, two full-scale arresters with different structures were exposed to successive nominal lightning impulses until failure, and it is found that the impulse failures of arresters are dominated by the structure and component. Surface flashover is the most common destruction for the varistor column. The cylinder type of varistors is suggested rather than hollow type, and the sleeve for position constraint of the cylinder varistor column should not be organic in order to avoid carbonization by arc discharge. It is found that the metallic spacers can contribute to sprayed-electrode protection, arc extinction, and heat dissipation. Based on the aforementioned results, an advanced arrester with structure optimization is proposed.

This paper presents the performance and protection of medium-voltage (MV) aerial cables against lightning faults by means of laboratory experiment and digital modeling. With the series of laboratory tests, practical examination of lightning hazard to shielded and unshielded aerial cables is conducted, and the need for shield wire protection is established. For the purpose of simulation studies, digital models are developed by using Alternative Transient Program-Electromagnetic Transient Program (ATP-EMTP) and its transient analysis of control system features. The performance of lightning flashover overvoltage on shielded and unshielded aerial cable is evaluated with the developed digital models. The evaluation is made by considering a direct lightning strike on wooden poles, messenger wires, and nearby trees. Based on the experimental and simulation results, practical recommendations are proposed for improvement in lightning performance of aerial cables. This study offers possible solutions for the protection of aerial cables against lightning flashover, induced overvoltage, and direct lightning strike, which may improve electricity reliability and availability to customers.

Given that currently available lightning protection measures cannot effectively protect overhead lines from lightning strikes, this study develops an active and fast arc-extinguishing lightning protection gap to address this issue. When a power frequency arc is formed within the protection gap due to a lightning strike, the lightning current immediately ignites the device, while strong airflow is synchronously produced. In this manner, the follow-up power frequency arc can be extinguished within an arc duration that is considerably shorter than the action time of relay protection; thus, relay protection can be avoided, and the lightning trip-out of overhead lines can be effectively prevented. A test of insulation coordination for impulse flashover and a test of power frequency arc extinction are performed to validate the effectiveness of the device. The arc-extinguishing test proves that the strong airflow can extinguish the arc within 0.4 ms. The devices have been widely applied in China and have been extremely successful.

DC power relay is a key electromechanical component widely used in electrical vehicles, photovoltaics, as well as more-electric aircrafts for energy managing, power conversion, and distribution. As the voltage and current increase due to relay switches, arc discharge becomes an unavoidable and significant issue during the operation of the dc high-power relay. Bridge-type contact and external permanent magnets are spontaneously employed in its arc chamber to accelerate the quenching of arc. In this paper, the complicated arc discharge plasma in a dc power relay has been investigated by using both experimental and numerical approaches. Initially, arc dwell and arc restriking characteristics during the arc motion phase are presented by analyzing the voltage and current waveforms and arc images acquired in carefully designed breaking experiments. The arc driven by a transverse magnetic field with a variety of flux densities and the influence of flux densities on arc voltage and dwell are preliminarily discussed based on the experimental results. Then, to reveal the arc physics and to determine the influence of transverse magnetic field on arc motion characteristics, a simplified model based on the magnetohydrodynamic (MHD) theory is built and three cases with different magnetic field are calculated. The simulated arc behaviors including distributions of the temperature and current density are presented. The mechanism underlying the influence of transverse magnetic field on the arc motion is analyzed according to arc root transfer and arc voltage variation. In addition, to understand the formation of the arc restriking, the critical breakdown electric-field strength inside the arc gap is also calculated based on streamer breakdown theory. The parameters in the space occupied by earlier arcs, as predicted by the MHD simulations, are used in the breakdown calculation. Results show that the critical breakdown voltage reduces remarkably along with growth of the operating voltage and breaking current, and the arc dwell time can be reduced by strengthening the external magnetic field within a reasonable extent.

Due to the wide application of high-order resonant and nonlinear electric equipment in the UHVDC converter station, the electromagnetic transient process is a complex issue during the short-circuit fault transient of the system caused by lightning strike or other reasons. In this study, firstly, an operating ±800 kV DC line is artificially short-circuited to simulate the flashover fault process. The instantaneous voltages and currents and the electrical fields are measured by advanced sensors and high sampling rate recording devices at different points in the converter station, in order to comprehensively study the high-frequency characteristics of the UHVDC system. Then, the portal impedances of the major UHVDC equipment as well as the stray parameters are systematically measured in an actual ±800 kV station. Based on the data measured, the accurate high-frequency characteristics of the ±800 kV converter station are analyzed. The results of the study can be used to guide the EMC and relay protection designs of the UHVDC converter station, so that the stability of the system can be improved.

Lightning is the main cause of transmission system outages, affecting reliability of power supply and resulting in economic losses. Shielding failure is an important issue in addressing the lightning performance of overhead transmission lines. In this paper an improved method based on the electro-geometric model is proposed to evaluate the shielding failure flashover rate (SFFOR) of transmission lines, considering the influences of landform, lightning polarity and stroke angle. In the improved method, the striking distances to phase conductors, shield wires and ground are properly differentiated by using recent equations developed to take into account other factors not only magnitude of lightning strokes. These factors include height of wires as well as lightning polarity. To reflect the effects of changes in terrain and height of wires on SFFOR, a method for identifying the topography and the relative position among the wires and ground is proposed. A 400-kV double-circuit transmission line section in complex terrain area was taken as example, and the results show that this method can reflect changes of the SFFOR along the span and can be useful to figure out which towers are easy to be struck by lightning along the entire transmission line. This research is helpful for the design and operation of overhead transmission lines.