A representative model of a three-story residential building incorporating a three-phase 22 kW electric vehicle (EV) charging station is developed in ATP-EMTP to investigate lightning-induced fast-front overvoltages. Direct negative and positive lightning strikes with peak currents of 10-200 kA and soil resistivities of 100-1000 Omega m are considered. Computed overvoltages at distribution boards, the EV charger, and the connected vehicle are compared against rated impulse withstand voltage (RIWV) levels to assess failure risk. The results show that, without low-voltage surge protective devices (SPDs), overvoltages exceed the RIWV of the charger and vehicle for all severe lightning scenarios. Protection schemes relying solely on distribution-board SPDs are insufficient, as critical overvoltages persist at the charger terminals. The installation of a dedicated SPD at the EV charger limits charger overvoltages to below 4 kV for all examined cases; however, the connected vehicle remains vulnerable for peak currents higher than 100 kA and high soil resistivity (> 700 Omega m). These findings demonstrate the necessity of EV charger SPDs and indicate the need for enhanced protection concepts for resilient residential EV charging infrastructure.

The effect of nanoparticle incorporation on the dielectric strength of natural ester oil is investigated under AC and DC high voltage stress. Iron oxide nanoparticles, Fe2O3, with a diameter of less than 50 nm, are used to produce nanofluids at six different concentrations, ranging from 0.0025% to 0.5000% w/w. The instantaneous breakdown voltage as well as the time to breakdown, and corresponding phase angle under AC stress, are recorded. Experimental results are analyzed to determine the statistical behavior of the AC and DC breakdown voltage in order to assess the relative improvement in the dielectric strength of nanofluids compared to the base liquid. Results indicate that the maximum enhancement in breakdown voltage under DC stress is approximately twice that achieved under AC, occurring at different nanoparticle concentrations. Findings are discussed taking into account the number of voltage applications, as well as nanoparticle accumulation and adhesion on test electrodes.

The growing need for eco-friendly insulating fluids in high-voltage systems has motivated the replacement of mineral oil with ester-based alternatives. The present investigation focuses on how SiC nanoparticles modify the dielectric behavior and thermal performance of synthetic ester-based nanofluids. Nanofluids containing 50 nm and 100 nm SiC particles at 0.002% and 0.004% w/w concentrations are prepared and characterized. The AC breakdown voltage and partial discharge inception voltage are experimentally determined according to IEC 60156 and IEC 60270, respectively, while thermal diffusivity and conductivity are also determined. The optimal composition (50 nm, 0.004% w/w) demonstrates an 18.8% increase in mean BDV and up to a 35.1% improvement at the 1% failure probability level, indicating enhanced dielectric reliability. Partial discharge measurements reveal a maximum PDIV increase of approximately 31% for the 50 nm formulation at 0.002% w/w. Thermal analysis shows enhancements of up to about 70% in thermal conductivity and around 62% in thermal diffusivity at 90 °C, confirming the multifunctional benefits of SiC addition. The results demonstrate that SiC-based synthetic ester nanofluids provide simultaneous electrical and thermal enhancement, promoting their use as next-generation eco-friendly insulating media for high-voltage equipment.

This work evaluates the effects of subsequent return strokes of negative downward lightning flashes on 150 kV and 400 kV overhead transmission lines through simulations carried out with ATP-EMTP software. The fast-front overvoltages stressing insulators due to direct lightning strikes to line towers and the associated minimum lightning peak currents resulting in backflashover are estimated for varying power-frequency tower ground resistance, considering median values for the parameters of the CIGRE lightning current waveform for subsequent strokes. Simulations were also performed for first return strokes considering the statistical variation of their waveform parameters. By comparing the results obtained for subsequent strokes with those for first strokes of the same peak current, it was observed that overvoltages due to subsequent strokes have a lower wavetail and a higher peak. The latter prevails resulting in lower critical backflashover currents for subsequent strokes. The waveforms of the overvoltages caused by subsequent strokes may vary rapidly after the peak due to reflections; this may affect the behavior of the leader development model used for predicting withstand or flashover of line insulation.

Insulating stand-offs are important components of an electrically insulated LPS towards preventing dangerous sparking between the components of the ILPS and metallic parts of the protected structure. In order to maintain the required separation distance, they shall be able to withstand the extremely high overvoltages arising on an electrically insulated LPS due to lightning strikes. Thus, for the safe and reliable design of an electrically insulated LPS, knowledge on the impulse surface dielectric behavior of insulating stand-offs is of great importance. The present study reports on an experimental investigation of the surface dielectric strength of insulating stand-offs subjected to standard lightning impulse voltages of both polarities. The surface dielectric strength is evaluated in terms of the 50% flashover voltage and flashover voltage-time characteristics. Contrary to that observed for 50% flashover voltage, for overvoltages the surface dielectric strength of the insulating stand-offs is lower under negative than positive impulses. Empirical expressions describing flashover gradienttime characteristics are derived. Also, flashover characteristics are well predicted by the integration method.

A typical 1 MVA charging station for electric cars connected to the overhead distribution system through underground medium voltage cables is modeled in the ATP-EMTP environment. Fast-front overvoltages impinging on the AC and DC sides of charging station equipment due to a wide range of lightning strikes to the incoming overhead medium voltage line are computed; positive and negative recorded lightning stroke currents are also considered. The risk of failure is evaluated by considering the rated impulse withstand voltage level of the charging station equipment by assessing the effects of lightning polarity, peak current, and soil resistivity. A protection scheme involving the installation of surge protective devices is investigated to diminish the risk of failure of equipment and interconnected charging cars. The energy absorption capability of surge protective devices against remote lightning strikes is assessed and the necessity of integrating surge protective devices to electric vehicles offering dedicated surge protection is discussed.

This letter examines the current-sharing behavior of a single-cell lithium iron phosphate (LiFePO4) battery connected in parallel with a zinc-aluminum varistor, aimed at protecting against fast-front impulse currents. Through experimental data analysis and ATP-EMTP simulations, the study explores the transient behavior of the protective varistor stack and the cylindrical LiFePO(4 )battery under surge events. Key factors considered include the determination of charge transferred to both the varistor and the battery as well as the voltage across their terminals. The findings highlight the challenges associated with surge protection against fast-front transients that threaten the reliability and lifespan of modern energy storage systems, particularly in safeguarding against lightning strikes and electromagnetic pulses.

This letter investigates the impact of gamma radiation on the transient performance of surge protective components under high impulse currents in the range of 0.3-2.0 kA generated by a 6 kV/3 kA combination wave generator. For the first time, the immunity of spark gaps, metal-oxide varistors, and transient voltage suppression diodes to gamma radiation is demonstrated by analyzing their residual voltage before, during, and after their exposure to a Cobalt-60 source for more than 4 minutes; samples were receiving a dose rate of 450 mGy/min. These findings (i) provide insights on test methodologies for international standards on surge protection and (ii) pave the way for implementation of surge protection schemes in highly irradiated environments, such as those encountered in the emerging power and data grids in aviation, space, nuclear, and defense industries.

This study presents a novel controllable impulse current generator tailored for incorporation into a power hardware-in-the-loop testing framework. The generator is capable of producing impulse current waveforms both computed via simulation software and recorded from real-world field data. This capability enables enhanced testing of surge protective devices and sensitive electrical and electronic equipment, supporting the advancement and deployment of next-generation surge protection technologies. Detailed technical specifications for both power and control circuits are outlined, with a comparison between targeted and recorded waveforms found in good agreement. An application of simulation-based impulse currents on various surge protective devices is provided, determining the use of this tool for insulation coordination and surge protection applications to address challenges of modern power systems.

The surge current withstand capability of transient voltage suppression diodes is experimentally investigated. With the aid of a combination wave generator, we apply a sequence of 8/20 mu s impulse currents with increasing peak with steps of 20 - 30 A to determine the surge current level that leads to failure mode the bidirectional diodes under study. Experimental results are analyzed and discussed in the context of power dissipation under surge events and potential leakage current changes under operating conditions.

Insulating down-conductors are utilized in electrically insulated lightning protection systems, LPS, to safely direct the lightning current to the earth, preventing dangerous sparking to conductive parts of the structure as well as damage caused by the flow of the lightning current. The protection afforded by a down-conductor system utilizing insulating downconductors depends upon the design of the air-termination system, that is, the number and positioning of the air terminals, as well as of the catenary wires. This study presents an evaluation of the overvoltages stressing insulating downconductor systems due to direct lightning strikes using ATPEMTP. Both partially and fully electrically insulated LPS of several designs are examined by considering direct negative first and subsequent lightning strokes. The lightning overvoltages stressing an insulating down-conductor are lower in a partially than a fully insulated LPS. A great reduction of both internal and external overvoltages is observed when the electrically insulated LPS utilizes multiple insulating down-conductors.

The prediction of the behavior of long air gaps and insulators, when stressed by fast-front overvoltages of non-standard waveshape, is crucial for evaluating the effects of lightning to power systems. This can be achieved in an accurate manner by applying leader development models (LDMs), accounting for the associated physical processes. This work contributes to LDM application to different methodologies/techniques used for the simulation of lightning strikes to power systems, and hence, for insulation coordination studies. This is achieved by identifying and discussing important features related to LDM implementation in a generalized manner not tied to a specific methodology and a specific LDM. Finite Difference Time Domain (FDTD) and ATP-EMTP implementations are introduced to investigate the effects of these elements. They are then employed to assess the lightning performance of a 150 kV single-circuit overhead power line. For this purpose, the minimum lightning currents causing shielding failure flashover and backflashover to the line are computed by means of the two aforementioned simulation methods. Results are compared and discussed considering the differences between methods. For the shielding failure case, identical results were obtained. Differences from <1% up to similar to 10% were found for the minimum backflashover current, and up to <5% for the backflashover rate.

This work reports part of an investigation on the relevance of positive cloud to ground return strokes as cause of backflashover in transmission lines. It denotes the lower amplitude overvoltages developed across insulators due to strikes of positive flashes in relation to those of negative ones and discuss the reasons for that. The results were obtained considering the physical and concise representations of tower-footing electrodes. It was revealed that it is feasible to represent the electrodes by their impulse grounding impedance, but that specifically calculated for the current of positive return strokes, notably that calculated from the peak of the current effectively flowing to the ground and respective GPR. The impact of taking the positive flashes into account according to dedicated procedure on the calculated lightning performance of the transmission line was very slight: an increase of about 5% in the backflashover probability for the conservative considered conditions.

This study investigates the transient response of battery packs comprising single-cell lithium iron phosphate batteries arranged in various configurations under fast-front impulse currents. As a case study, the voltage across the battery pack terminals and the current through them were measured for impulse currents ranging from 0.1 to 5.1 kA. The findings highlight the transient behavior of battery packs, focusing on key aspects such as transient peak voltage, impulse current, and charge distribution among individual cells composing battery packs under fast-front transients. The analysis demonstrates the significant impact of the transient impedance of both the connecting leads and the single-cell batteries, often negligible during low-frequency operation, which can lead to imbalances in charge transferred among the cells, ranging from 1.1 to 7.6 times. This research highlights the challenges in manufacturing techniques and surge performance, focusing on the complexity of battery pack behavior under fast-front transients. It signifies that equal-length leads alone cannot achieve perfect current sharing, necessitating further investigation to enhance the reliability and resilience of modern energy storage systems. Advancing these technologies is essential for ensuring safety and mitigating degradation under extreme conditions, such as lightning strikes and electromagnetic pulses.

This study introduces a modeling approach for the transient response of batteries against fast-front impulse currents. An experimental methodology is presented to allow time-domain simulation of the surge performance of the battery using a straightforward process that involves mathematical analysis of the experimental records. A lithium iron phosphate battery was used as a case study; the voltage across the battery terminals and the current flowing through them is recorded for a range of 0.1 to 5.0 kA generated through a combination wave generator (12 kV 1.2/ 50 mu s, 6 kA 8/ 20 mu s). The developed non-linear equivalent circuit model yields results in very good agreement with experimental data of standard and non-standard impulse currents with a wavefront duration longer than 3 mu s and time-to-half up to 60 mu s. This work provides an advanced framework for surge protection of battery systems contributing to reliability and resilience of modern power grids against lightning events and electromagnetic pulses

The dielectric strength of natural ester oil-based nanofluids with varying nanoparticle concentrations is experimentally investigated under AC, DC and lightning impulse voltages. Experimental results are analyzed to determine whether there is an optimal concentration of iron oxide nanoparticles which enhances the dielectric strength of the base liquid under various high voltage stress. A different effect of nanoparticle concentration on dielectric strength is found for AC, DC and lightning impulse voltages; no single concentration among those tested (0.005% w/w, 0.050% w/w, 0.500% w/w) was identified as universally optimal across all voltage types.

Photographic records of natural lightning leaders obtained through high-speed video camera observations based on a literature review are analyzed. The fractal dimension of the downward stepped leaders during negative downward flashes is estimated. Two methods, the box-counting and sandbox methods, are employed for fractal dimension calculation, utilizing algorithms developed in MATLAB software; appropriate image processing techniques are utilized to ensure accurate fractal dimension estimation and ensure impartiality of the results. A discussion is made through a comparison of the estimated fractal dimension with values previously reported in the related literature; the possible effect of lightning peak current on the fractal dimension is also examined. Results of this work may assist in accurate modeling of the lightning attachment phenomenon leading to a safer design of the lightning protection system of power systems.

Electrically insulated lightning protection systems, LPS, utilize insulating stand-offs and insulating down-conductors to maintain the required separation distance from grounded objects. An equivalent separation distance offered by these insulating components can be determined through comparative tests, such as those suggested in IEC TS 62561-8:2018, where crossed-conductors air gaps under negative standard lightning impulse voltages are used as reference. However, in service the insulating components of an electrically insulated LPS are stressed by non-standard fast-front overvoltages related to lightning return-stroke currents. In this study the electric stress experienced by the insulating components of an electrically insulated LPS utilizing a single air terminal, connected to the grounding system via an insulating down-conductor, due to direct negative lightning flashes is assessed through ATP-EMTP simulations. The ground resistance of the LPS grounding system, the length and the resistance of the semiconductive screens of the insulating down-conductor, as well as the characteristics of the lightning return-stroke current were considered as parameters affecting the fast-front overvoltages. For an evaluated electrically insulated LPS the critical lightning currents causing failure of internal and external insulation can be determined; thus, creepages and clearances, as well as the dielectric strength of internal insulation ensuring a safe design against lightning overvoltages can be determined.

The transient behavior of commercially available low-voltage surge protective devices (SPDs) is experimentally investigated by employing standard lightning and switching impulse voltages. The response time of an SPD that integrates a triggered spark gap between the power lines and earth is on focus; a novel definition of the response time is proposed. Surprisingly, the experimentally derived response time varies beyond the upper limit declared by the SPD manufacturer. This work stresses the need for an update of international standards to incorporate a definition of the response time of SPDs covering a wide range of transients.

This work investigates the efficacy of different experimental and simulation methodologies in determining the parasitic inductance of surge protective devices for a broad frequency spectrum. This is important since the inductive behavior of surge protective devices affects their maximum residual voltage, thus also the protection offered in the case of fast-front transients exhibiting high current derivatives. The parasitic inductance of a commercially available DIN rail surge protective device is determined by utilizing a dummy surge protective device with the voltage limiting component (varistor) replaced by a copper block. Parasitic inductance estimations are made by employing: i) dielectric spectroscopy measurements, ii) impulse current tests, and iii) finite element analysis simulations; results are discussed in terms of the accuracy of the proposed methods and associated challenges in determining the parasitic inductance.