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This article investigates the application of the pulse voltage method for detecting interturn short-circuit faults in the high-voltage windings of dry-type voltage transformers. We determined the characterization parameters of the high-voltage windings of dry-type voltage transformers and trends in the variation of the characterization parameters with frequency in the presence and absence of faults. The viability of using the pulse voltage method for the detection of interturn short-circuit faults in dry-type voltage transformers was analyzed. A pulse voltage test platform was designed to analyze the response voltage waveforms using pulse-oscillating voltage experiments on transformers with various short-circuit faults. The results demonstrate that during a turn-to-turn short circuit, the equivalent resistance and inductance of a high-voltage winding are significantly lowered. When employing the pulse voltage method to investigate interturn short-circuit faults, tiny inductors are connected in parallel to produce an oscillating voltage waveform that is more uniform. Upon incurring a short circuit between turns, the pulse's oscillating voltage frequency increases. The greater the number of turns in the short-circuit fault is, the more significant the effect of the test. [ABSTRACT FROM AUTHOR]

The main aim of the article is to demonstrate the effectiveness of the use of ground penetrating radars to assess various objects using the example of assessing the current state of highways. The article uses the software developed by the authors and the corresponding mathematical models. The analysis of the results obtained is based on mathematical models that have proven their effectiveness and is time-tested. It should be emphasised that the main problem in assessing roads with non-rigid pavement is associated with a change in the main parameters of the layers – thickness and dielectric constant. Previously, we proposed a scheme for the layer-by-layer determination of the values of the relative permittivity and then - the subsequent determination of the thickness of each layer, starting from the top layer and ending with the base. The paper presents the results of experiments actually carried out by the authors with various GPRs, which not only have different values of the central frequency, but also have significant design differences. In addition, the results of processing real data using the software developed by the authors are presented. As a result, an improved method of signal calibration has been proposed, which makes it possible to increase the reliability of assessing the thickness of road surfaces, as well as other objects.

This article investigates the application of the pulse voltage method for detecting interturn short-circuit faults in the high-voltage windings of dry-type voltage transformers. We determined the characterization parameters of the high-voltage windings of dry-type voltage transformers and trends in the variation of the characterization parameters with frequency in the presence and absence of faults. The viability of using the pulse voltage method for the detection of interturn short-circuit faults in dry-type voltage transformers was analyzed. A pulse voltage test platform was designed to analyze the response voltage waveforms using pulse-oscillating voltage experiments on transformers with various short-circuit faults. The results demonstrate that during a turn-to-turn short circuit, the equivalent resistance and inductance of a high-voltage winding are significantly lowered. When employing the pulse voltage method to investigate interturn short-circuit faults, tiny inductors are connected in parallel to produce an oscillating voltage waveform that is more uniform. Upon incurring a short circuit between turns, the pulse’s oscillating voltage frequency increases. The greater the number of turns in the short-circuit fault is, the more significant the effect of the test.

The standard 1.2/50 lightning impulse test has been important for factory testing equipment and evaluating their performance in electrical systems. In practice, however, such equipment is subject to non-standard waveform (NSW) of high frequencies, which may not be covered by standard tests. To overcome this difficulty, the present article outlines a method that simulates NSW in laboratory tests. Based on multiresolution wavelet analysis, the method considers the correlation between amplitude and entropy in the decomposition levels between waveforms. To that end, changes are proposed to the following parameters of standard impulse tests: amplitude, cut-off instant, and front time. The results show that, mostly, the combination of a lightning impulse waveform (LIW) with impulse waves cut at different times, sufficiently represent the NSW. Only when the NSW's density falls predominantly in a frequency range above 3.125 MHz, will there be need for a complementary LIW with a steep front time. The method's application allows manufacturers and concessionaires to subject the equipment to conditions that properly represent the NSW effects, through lightning impulse tests carried out at the factory. [ABSTRACT FROM AUTHOR]

Impulse waveforms have been widely used in the studies of streamer and breakdown phenomena in dielectric liquids. In this article, both experiments and analyses were carried out to investigate the effects of impulse tail-time on streamer and breakdown characteristics of a mineral oil and a synthetic ester liquid. A range of positive impulse waveforms with the same front-time of $0.8~ \boldsymbol {\mu } \textrm {s}$ but different tail-times from 8 to $3200~ \boldsymbol {\mu } \textrm {s}$ were considered. Needle-plane electrodes with a needle tip radius of 10 $\boldsymbol {\mu } \textrm {m} $ and a gap of 10 mm were used. It was found that reduction of tail-time leads to an increase of 50% impulse breakdown voltage, while the instant breakdown voltage and the time-to-breakdown remain constant. On this basis, an analytical method is developed to estimate the 50% impulse breakdown voltage under waveforms with various tail-times. The method is valid when streamers remain of second mode and in divergent fields. It was also observed that some “self-regulation” by branching explains the constancy of streamer propagation velocity when the applied voltage is increased. [ABSTRACT FROM AUTHOR]

Partial discharge (PD) due to high dv/dt pulsewidth modulation has been identified as one of the leading causes of insulation failure in low voltage (LV) variable frequency drive (VFD) fed motors with random wound stator windings. With the recent increase in electrical stress with faster risetime wide bandgap power semiconductor devices and higher dc link voltage for higher efficiency and power density of the system, PD-induced insulation failures are expected to increase. Since LV motor insulation is not resistant to PD, an increasing number of VFD motors are being qualified for PD-free operation. However, the PD inception voltage of qualified motors decreases with insulation aging making LV motors susceptible to failure. In this article, an offline standstill test method is proposed for automated inverter-embedded PD testing under impulse excitation. The main concept is to perform the impulse PD test using the VFD at increased voltage levels for providing advanced warning of PD activity for preventing forced outage of VFD motors. Options for application of increased impulse test voltage and automated detection of PD for implementing the proposed concept are presented. Testing on an 800 V VFD driven motor shows that the proposed method can provide automated impulse PD testing whenever the motor is at standstill to warn the end user of impending PD activity that can lead to failure. [ABSTRACT FROM AUTHOR]

Long‐term stabilities of shielded resistive voltage dividers for lightning and switching impulse, employed as the reference dividers of Japan High‐voltage Impulse testing Laboratory Liaison (JHILL) are investigated. The DC scale factors and the step‐response parameters have been annually measured for 20 years. Annual variations of impulse parameters, namely the peak value, the front time, and the time to half value of the calculated waveform from the step‐response waveforms by the convolution algorithm are investigated. Furthermore, long‐term stabilities of reference low‐voltage impulse calibrators are investigated. The parameters of circuit elements of the calibrators have been annually measured for 18 years. The impulse parameters of the output waveforms of the calibrators are calculated, and the annual variations of them are investigated. After the detailed evaluation, it can be expected that the measurement system employing the voltage dividers and the calibrators, including the analytical method of the data, has the similar performance to those of NMIs of developed countries. © 2021 Institute of Electrical Engineers of Japan. Published by Wiley Periodicals LLC. [ABSTRACT FROM AUTHOR]

The performance of a high-voltage switching impulse (SI) measurement system is highly dependent on the characteristics of the used voltage divider. Self-built or commercial voltage dividers do not always fulfill the requirements set for reference-level devices. Software corrections to improve the non-ideal divider response are easy to implement. This article describes the traceability and performance of the SI measurement systems of VTT MIKES up to 400 kV. Traceability is based on a calculable impulse voltage calibrator, which is used for calibration of a reference digitizer and a 10-kV divider. The 10-kV divider is then used to calibrate the 400-kV modular divider. Responses of both dividers are corrected using two different software methods. Implementation of these software methods allows state-of-the-art impulse parameter uncertainties. The most significant uncertainty component of time to peak is related to its definition and evaluation according to IEC 60060-1:2010 and IEC 61083–2:2013. [ABSTRACT FROM AUTHOR]

A force-driven kinetic energy harvester, designed to be excited with impulse-like mechanical loads, is presented. Energy harvesting is a promising technique to feed wireless sensor networks. The proposed device exploits three rods of Galfenol and has been modeled through FEM COMSOL Multiphysics with nonlinear fully coupled characteristics. They consider the general behaviors of magnetostrictive materials and are compatible with thermodynamics. The preliminary results of the time-domain simulations, with an impulse-like force applied, have been compared with experimental results showing a good agreement. Moreover, the proposed nonlinear modeling has shown better performances with respect to software built-in magnetostrictive models. At the same time, further modeling improvements seem to be needed in the future to better fit the harmonic content of the free evolution of the device. [ABSTRACT FROM AUTHOR]

Based on the LaSalle invariant principle of stochastic differential equations and the graph theory, several sufficient conditions are obtained by adaptive feedback control and impulsive control. The error dynamical system is globally almost surely asymptotically stable. The conclusion is new and feasible. Finally, an example is given to show the validity of the results.

The thermal behaviour of the surge arrester is vital to assess its operational condition. The surge arrester usually shows a process of temperature rising during a long-term operation, particularly after subjecting to a surge. Therefore, the research on the temperature characteristics of ZnO arresters contributes to achieve the goal of the performance changes of the ZnO arresters over different temperatures. In this study, based on four types of ZnO arresters from different factories, the variation of the volt–ampere curve, DC characteristic parameters and non-linear coefficient of the whole ZnO arrester at different temperatures were analysed. The relationship between the temperature and non-linear coefficients was obtained through the method of the extraction of the non-linear coefficients. Through the multiple impulse current tests, the temperature of the arrester was well calculated by measuring the corresponding volt–ampere curve, and the relationship between the surface temperature and V–I characteristics of the arrester is verified by the impulse test results. The obtained results provide a new idea for the application of the surface temperature of the arrester in the performance monitoring of the arrester. [ABSTRACT FROM AUTHOR]

An active gas surge protection gap (SPG) and its energy coupling trigger circuit were designed in this study. In the lightning voltage impulse test, the active SPG had better protection characteristics than the passive SPG. To investigate the influence of the trigger circuit on the protection characteristics, the transient voltage and current characteristics of each electrical component in the active coupling trigger circuit were discussed. The equivalent model of the active trigger circuit was established, and the correlation between the active SPG protection characteristics and the active trigger circuit parameters was derived. According to the relationship, the theoretical breakdown characteristics of the active SPGs can be obtained by MATLAB. The deviation between simulated results and experimental data was no more than 11%. Based on the simulation, the design principles of the active energy coupling triggering circuit were proposed, laying the foundation for the theoretical research and engineering application of active SPGs. [ABSTRACT FROM AUTHOR]

The reliable technique for identification of winding insulation faults in a transformer is necessary for a testing engineer during impulse test. In this study, a statistical correlation technique is proposed to estimate the 'best correlation' between transient signals for passed (withstood the impulse voltage) or failed (not withstood) conditions of the insulations. In this study, normalised reduced impulse voltage is considered initially as a reference signal. The next successive impulse test sequences due to rated test voltage are correlated as a test signal with a reference signal using a proposed technique. It makes a 'good correlation value along with its directions' between the reference signal and test signal based on measured the applied impulse voltage waveshape and its winding response. The fundamentals of the correlation coefficient, curve fitting techniques, conditional variance, normalisation and time delay index are integrated effectively to predict the characteristics (degree/magnitude and direction) of correlation between the signals. 2.5‐MVA 11/0.433 kV (distribution transformer), 0.3‐MVA 34.5/0.415 kV (earthing transformer) and 250‐MVA 500/275/33 kV (power transformer) are effectively utilised to validate proposed technique. The advantage of the proposed technique is validated with partial discharge detection in windings due to an impulse voltage application using an 11 kV single‐layer winding. [ABSTRACT FROM AUTHOR]

Partial discharge (PD) has been identified as one of the root causes of stator insulation failure even for low voltage (LV) ac motors. For reliable operation of variable frequency drive motors, a standard acceptance test procedure (IEC STD 60034-18-41) to ensure PD-free operation of LV motors was developed. Although the test can verify whether PD exists in the stator for a surge with predetermined voltage level and risetime, the information on where PD activity is present in the stator insulation is not provided. In this article, a test method based on a new variable risetime surge generator is proposed for identifying the component of stator insulation where PD occurs in LV random wound stators. The proposed test allows the user to locate whether PD is in the turn, phase, or ground insulation. This information is critical for lowering the PD inception voltage for improving the motor reliability through insulation system design/manufacturing or motor/drive system reconfiguration. The test is implemented with a 4.5 kV variable risetime surge generator prototype, and seven LV ac motors are tested to show where PD is likely to occur in commercial LV motors. [ABSTRACT FROM AUTHOR]

High entrance capacitances of ultrahigh-voltage (UHV) transformers make it difficult to generate impulses with standard front time during the lightning impulse tests. In this paper, we discuss the feasibility of examining the longitudinal insulation design of a transformer via impulses with a front time longer than the standard value. We consider the following features: transient voltage distributions and insulation characteristics of longitudinal insulation. The transient voltages of two UHV windings are measured with a capacitive voltage sensor under impulses with different front times. The results demonstrate that the front time of the applied impulse has little effect on the gradient voltage distributions and the oscillatory component of the transient voltage, but it determines the front time of transient voltages. Therefore, the relationship between breakdown characteristics of the turn-to-turn insulation and the front time is studied. Experimental results revealed that whatever the insulation thickness, an increase in the front time of the applied impulse decreases the breakdown voltage, but this variation is within acceptable tolerance when the front time changes from 1.2 μs to 6 μs. Thus, as long as the front time is restricted within 6 μs, we can ensure the validity of lightning impulse tests on the examination of longitudinal insulation designs. [ABSTRACT FROM AUTHOR]

The breakdown and streamer behavior in double-layer oil-paper insulation under impulses of varying front time were investigated in this study to determine the prebreakdown process in oil-paper insulation. The relationships between front times and breakdown characteristics were investigated and impulse-polarity-dependent variations were observed. The complete impulse breakdown process and precise role of front time were assessed as per streamer initiation and streamer propagation based on emitted light signals and shadow images. The re-initiation of streamers in non-first oil gaps was determined to be the key factor in breakdown as-dominated by applied voltage and space charge accumulation. The initiation and propagation times of streamers were observed to find that the streamers tend to propagate at phases with higher voltage amplitude as front time increases, which facilitates streamer re-initiation and thus decreases the breakdown voltage. Equivalent applied voltages during streamer propagation were further calculated to quantitatively investigate the effect of front time on streamer propagation. [ABSTRACT FROM AUTHOR]

The disconnector is the key electrical equipment in DC field. In China, the ±1100 kV DC project uses the indoor DC field, where the switching impulse withstand voltage of the disconnector influences the clearance a lot. To improve the switching impulse withstand level of the ±1100 kV disconnector, first of all, the switching impulse test was carried out on the disconnector with traditional double-balanced ring structure and the 50% switching impulse discharge voltage was obtained. By analysing the discharge path, it is found that the grading ring did not effectively shield the upper part of the disconnector. Therefore, the structure of the end fittings of the disconnector was changed to the structure of the mushroom head. The electric field simulation was performed on the optimised shield，it is shown that the maximum field strength is lower than the control field strength. Then the switching impulse test was carried out on the optimised disconnector, it was found that the 50% impact discharge voltage was above 2400 kV which met the engineering requirements.

Partial discharge inception voltage measurements under repetitive impulsive voltages play an essential role in evaluating the reliability of inverter-fed low voltage rotating machines. Using impulsive voltages, partial discharge (PD) signals and the disturbance induced by power electronics switches have often similar energy distribution in the frequency domain. Thus, PD test technologies used with sinusoidal voltages are no longer effective. Under repetitive impulsive voltages, ultra-high frequency detection is recommended to couple high-frequency spectral components from the PD and remove the low-frequency disturbance coming from power electronics. However, to obtain high signal to noise (S/N) ratio, the parameters of the antenna used for PD detection should be designed considering the PD and the disturbance energy distributions in the frequency domain. In this paper, we discuss the design and show the properties of an antenna with Archimedes plane spiral structure intended for PD detection under repetitive impulse voltages. The simulation shows that the antenna has low voltage standing wave ratio (<2) and improved directivity in the frequency range from 0.5 to 2 GHz. Moreover, PD tests performed using repetitive square waves with different rise times demonstrate that the designed antenna can receive PD signals efficiently with high S/N. [ABSTRACT FROM AUTHOR]

The disconnector is the key electrical equipment in DC field. In China, the ±1100 kV DC project uses the indoor DC field, where the switching impulse withstand voltage of the disconnector influences the clearance a lot. To improve the switching impulse withstand level of the ±1100 kV disconnector, first of all, the switching impulse test was carried out on the disconnector with traditional double-balanced ring structure and the 50% switching impulse discharge voltage was obtained. By analysing the discharge path, it is found that the grading ring did not effectively shield the upper part of the disconnector. Therefore, the structure of the end fittings of the disconnector was changed to the structure of the mushroom head. The electric field simulation was performed on the optimised shield，it is shown that the maximum field strength is lower than the control field strength. Then the switching impulse test was carried out on the optimised disconnector, it was found that the 50% impact discharge voltage was above 2400 kV which met the engineering requirements. [ABSTRACT FROM AUTHOR]

Surface flashover characteristics of insulation materials in vacuum are key factors to determine the behavior of high voltage electrical equipment. Although the surface flashover in vacuum has been investigated for decades, the surface insulation properties of polymeric materials after repeated surface discharges have shown little attention by researchers. In order to investigate the aging characteristics of polymeric materials caused by repeated flashovers in vacuum, several typical materials were used to flashover by microsecond pulses. The flashover voltages were obtained for polytetrafluoroethylene, polymethylmethacrylate and polyamide for thousands of flashovers. The surface morphology of samples was observed after different numbers of flashovers. The trap parameter distribution was obtained by the isothermal surface potential decay method. To analyze the flashover voltage change with discharge times, the Weibull distribution was used to determine the conditioning and degradation effects in repeated discharge experiments. The results show that the morphology near the cathode triple junction and deep traps together affect the subsequent flashover voltage. The conditioning and degradation phenomena often coexist in the aging process of polymers and affect the surface insulation properties. This study could provide a reference for the type selection, design, and modification of insulation materials in vacuum. [ABSTRACT FROM AUTHOR]

This article presents a model of Sparking Gap to be used in the Alternative Transients Program (ATP). The model includes the simulation of breakdown and a representation of the electric arc. The arc will be non-constrained and burn in air at atmospheric pressure, thus a discussion of the model and parameters to be used is presented. The effect of the arc on the interruption of current will be studied. Examples of power arc interruption following an impulse impact on a 230 kV transmission line are presented. The effects of interphase capacitive coupling and line length are discussed, in order to establish guidelines to allow successful reclosing operations. [ABSTRACT FROM AUTHOR]

We developed a new prediction technique for dynamic stress on a bellows with low computational load, to secure the strength reliability of the multilayer bellows used in the engine exhaust system of hydraulic excavators. In this developed technique, dynamic stress is predicted by constructing the bellows finite element model with single-layer shell elements having stiffness equivalent to that of the multilayer bellows and selecting appropriate excitation conditions for each stress-generating factor. The stress time waveform calculated by the developed prediction technique was verified by actual measurement results, and the following conclusions were obtained: (a) The causes of dynamic stress on the bellows were specified and classified into the two classifications. One is the deformation of the bellows caused by relative displacement. The other is the deformation caused by the bellows vibration modes; (b) Appropriate excitation conditions of the bellows model are forced displacement input for predicting dynamic stress caused by relative displacement, and forced acceleration input for predicting dynamic stress caused by the bellows vibration modes; (c) The calculation results derived by using the above model and the excitation inputs were verified by measuring a vibration bench test. The calculated stress had relative agreement with measured stress in the test.

Even for gas-insulated metal-enclosed switchgear (GIS) equipment that has passed an on-site dielectric test, some dielectric failure can occasionally occur without warning. It is necessary to evaluate the effectiveness of on-site dielectric tests of GIS equipment. In this study, two standard test procedures, power-frequency partial discharge (PD) and lighting impulse (LI) withstand test, were carried out in a real model test platform of 550 kV GIS to evaluate the effectiveness of on-site dielectric tests. Through experiments, the minimum detectable defect sizes were determined for different curvature radius values. The results show the limitation of the power-frequency PD test and the need to use of the LI withstand test as supplementary assessment on site. Two calculable constraints of defect detectability were proposed to extend the results to GIS equipment at other voltage levels. The results clarify the cause of dielectric failure without any warning and provide technological guidance for manufacturing and installation. [ABSTRACT FROM AUTHOR]

There has been a vast vacuum in the literature on the importance of the location of remote earth carried out during impulse test on grounding systems using field measurements. Some published work show that the remote earth is installed surrounding the electrode under tests, whilst some have used separate remote earth, away from it. This work studies the impact of return electrode location on transient behaviour of the earthing electrode. The electrode under test is a single rod. Two types of remote earth configurations are used, a circular electrode with multiple rods surrounding the single rod, and one that is 80 m away from it. Impulse tests are conducted under both impulse polarities. Voltage and current traces are captured for a single rod, using two different types of remote earth configurations, with the impulse resistance measured as well. It has been established that the arrangement of the remote earth poses no influence on the test results. That said, higher oscillations of current traces and higher resistance values have been observed in negative impulse in comparison with positive impulse polarities. [ABSTRACT FROM AUTHOR]

This paper presents the results of the application of a novel method to estimate the parameters of the Disruptive Effect Model for the prediction of the volt–time curves of 15 kV insulators. Besides the standard lightning impulse voltage waveshape, four non-standard impulse waveshapes (namely 1.2/4 μs, 1.2/10 μs, 3/10 μs, and 7.5/30 μs), of both polarities, were adopted in the tests. The measured volt–time characteristics of a 15 kV class pin-type insulator were compared with those predicted by three different procedures related to the Disruptive Effect Model: Darveniza and Vlastos, Hileman, and the one recently proposed by the authors. The results show that for some impulse waveshapes and polarities, the methods by Darveniza and Vlastos and by Hileman do not predict insulator breakdown for the lower voltage levels. On the other hand, a relative good agreement is found between theoretical and experimental results for the calculations performed using the method proposed by the authors. [ABSTRACT FROM AUTHOR]

A concept to predict the Lightning Impulse Voltage (LIV) breakdown probability of medium voltage Vacuum Interrupter (VI) tubes has been developed and tested for the first time employing the Voltage Holding Prediction Model (VHPM) originally formulated at Consorzio RFX. The VHPM is capable to calculate the Weibull breakdown probability curve of any multi-electrode multi-voltage system insulated in vacuum under dc voltage. Even though the possibility to employ the VHPM in the prediction of voltage breakdown under LIV conditions is not straightforward, the potential benefits of the VHPM usage in VI tube technology with regard to development, design and testing at medium and high voltage levels, strongly recommend the assessment of VHPM under LIV conditions. The paper aims to describe the methodology adopted to identify experimentally the VHPM parameters to be employed in such a novel application to assess its prediction capability. The measurements have been done in the Siemens Berlin VI tube factory test stand for LIV, compliant with the IEC standard. Different vacuum tube types manufactured by Siemens were investigated. The main difficulty was to obtain, with such a test bed, voltage breakdown distributions well fitted by a Weibull Distribution — upon which the VHPM is based — primarily due to the difficulty to reach a well-defined end of the conditioning test sequence preceding the relevant voltage breakdown test sequence suitable to be analyzed by the VHPM. Nevertheless, the VHPM prediction resulted in reasonable agreement with the measured probability curves. Finally, investigating VI tubes with spiral-type Radial Magnetic Field (RMF) contacts, characterized by a geometry strongly deviating from axial 2-D symmetry, the first implementation of a full 3-D version of the VHPM has been tested. [ABSTRACT FROM AUTHOR]

This paper presents a fast and precise method for the calculation of internal voltage transients over the voltage instrument transformer windings. Lumped circuit parameters of the transformer winding are calculated using self-developed solvers based on the boundary element method and integral equations approach. A detailed equivalent circuit of the transformer winding is solved in time domain. Test model of the voltage instrument transformer is constructed with a number of measurement points along the windings. Results of the calculation are in a good agreement with the measured voltages. [ABSTRACT FROM AUTHOR]

Este artículo presenta los resultados de dos tipos de pruebas hechas a una clase de arena para obtener los valores de resistividad y permitividad eléctricas en el rango de los Hz hasta los MHz. Una de las pruebas fue realizada a frecuencias específicas con un generador de señales, y la otra fue hecha con un generador de impulsos de tensión, con lo cual se trabajó un espectro continuo de frecuencias. Las pruebas se llevaron a cabo para tres valores de humedad, y los resultados de ambas mostraron un comportamiento no lineal presente en la superficie de los electrodos de prueba. Esta no linealidad fue modelada y considerada en el procedi-miento de cálculo de los valores de permitividad y resistividad en el dominio de la frecuencia. Finalmente, se señalan los resultados, las conclusiones y el trabajo futuro.

The impacts of a lightning strike are amplified in an environment with special features such as a ship electric grid, especially within the extended integration of electronic systems. In most marine regulations, lightning protection specifications are inadequate in the cases of metallic vessels, regarding the necessity of installing lightning rods and the method for the definition of their protection zone and subsequently of their height. Therefore, impulse voltage experiments on a scaled‐down ship model were conducted in order to acquire interception probability distributions of its superstructures and to assess the accuracy of various protection zone models, established for isolated rods, on the given complex topology of a ship. The experimental results highlighted the overestimation of the protection zone even by the well‐established rolling sphere model for negative polarity impulses depending on the geometrical conditions and the satisfying performance of statistical models that incorporate proximity effects and lightning interception probability. [ABSTRACT FROM AUTHOR]

This study focuses on partial discharges (PDs) in the gaseous void in an insulator under aperiodic switching impulse (SI) and oscillating SI (OSI). The PD measurements are carried out using a 110-kV GIS model with an artificial known void defect in a basintype insulator. Experiments show that the PD sequences under SI and OSI are composed of the main discharge, which occurs at the rising edges or the peaks of the applied impulse, and the polarity reverse discharge, which occurs at the falling edges or troughs. For a new sample, the 50% PD inception electric field (PDIE50) under different stress types obviously decreases with increasing void radius, and their values follow the pattern PDIE50, OSI > PDIE50, SI > PDIE50, AC. For an aged sample, the difference between the experimental PDIEs and the streamer inception value becomes close. The relationships between the time lag and the applied voltage can be calculated by the V?t curves, which roughly describe the distribution of the time lag under impulses. The experiment indicates that OSI can more easily excite PD compared with SI. Repeated tests show that the magnitudes and numbers of the main and reverse PDs gradually change as the test is repeated. [ABSTRACT FROM AUTHOR]

SF6 is widely used in modern transmission and distribution networks because of its outstanding dual qualities: arc quenching and dielectric insulation. As a gas medium, SF6 is chemically inert, non-toxic, and non-flammable, which makes possible the construction of compact SF6 switchgear. One major known disadvantage of the gas is that it has a global warming potential which is 23,900 times higher than CO2. This has led to research into alternative gases with a much lower environmental impact, and one of the emerging candidates is CF3I. The high boiling temperature of CF3I means that it has to be used as part of a mixture inside gas-insulated equipment. To carry out the investigation on CF3I, a scaled-down coaxial system that replicates the maximum electric field of a 400 kV GIL system was designed and fabricated. The insulation performances of CF3I/CO2 and CF3I/N2 gas mixtures were then examined by measuring the 50% breakdown voltage, U50, using a standard lightning impulse waveform (1.2/50) under absolute pressures of 1 to 4 bar. The experimental results show that CF3I gas mixtures have promising potential as an insulation medium for application in gasinsulated lines. [ABSTRACT FROM AUTHOR]

This paper presents an evaluation of the performance of different methods for estimating the parameters required for the application of the Disruptive Effect Model to the analysis of the breakdown characteristics of 15 kV distribution insulators subjected to lightning impulses. The tests involved the application of both the standard (1.2/50 μs) and non-standard lightning impulse voltage waveshapes (1.2/4 1.2/10 3/10 μs) and 7.5/30 μs)of positive and negative polarities. The obtained Vxt characteristics are compared with those predicted by the Disruptive Effect Model using the most common procedures for estimating the parameters necessary for its application, including a novel method which is presented in the paper. An analysis of the results relevant to the various procedures shows that the parameters obtained according to the proposed method lead to a better agreement between theoretical and experimental results. [ABSTRACT FROM AUTHOR]

This paper describes IMPREAL 2.0, a system developed in LabVIEW that automates the acquisition of voltage impulse waveforms from digital oscilloscopes and implements the mathematical procedures described in the new standards from the International Electrotechnical Commission IEC 60060:2010. The system controls commercial digital oscilloscopes and is able to automatically calculate the time and amplitude parameters of lightning impulses (LI), switching impulses, chopped LI, and oscillating impulses (lightning and switching) waveforms, generating test reports tailored for the needs of the calibration and tests labs. The estimated uncertainty due to the software processing is also presented here, following the guidelines defined by standard IEC 61083-2:2013. [ABSTRACT FROM PUBLISHER]

The International Electrotechnical Commission (IEC) issued in 2010 a revision of the family of standards IEC 60060, describing, among other requirements, how to calculate the various amplitude and time parameters used to evaluate high-voltage impulse waveforms. However, the standards are not clear in some aspects, especially when describing tail-chopped lightning impulses. This paper aims at describing in detail how to properly estimate the time parameters of such impulses. [ABSTRACT FROM PUBLISHER]

This paper describes the establishment of a large-area outdoor experimental facility at the Dinorwig pumped-storage power station in North Wales for investigating the performance of practical grounding systems. The facility itself and arrangements of test electrodes and measurement equipment are described, providing a background for subsequent test methodologies. In addition, tests to determine the variation in the water and reservoir bed resistivities have been undertaken, resulting in a survey data set that better informs experimental work and simulations of vertical ground rod and grid electrodes. It is proposed that this facility may also be used to calibrate grounding meters and for validating computational modelling techniques. In a complementary paper, results of low-voltage dc, ac, and impulse tests of varying magnitudes are described, and experimental results are compared with computed values obtained from numerical models. [ABSTRACT FROM AUTHOR]

This paper presents tests carried out at an outdoor experimental facility, described in the companion Part 1 paper, to investigate the performance of practical grounding systems. Here, the results of low-voltage dc, ac, and impulse tests performed on rod and grid electrodes are described, and the measured quantities are compared with computed values obtained from numerical models. Measured ground resistance and impedance at low frequency (including power frequency) showed reasonable agreement with simple standard formulae and computational models, but revealed a significant falloff with current magnitude in the range often used for practical testing of high-voltage grounding systems. This may have implications for the specifications of grounding test equipment and extrapolation of measured ground resistance/impedance at low-voltage/current to values representative of realistic fault currents. A frequency dependence of ground impedance was also measured. Specifically, a fall in impedance over a frequency range up to 100 kHz is not generally accounted for in grounding models. [ABSTRACT FROM AUTHOR]

This paper explores multiple impacts generated through fixture design to induce high accelerations in board level drop testing. Drop tests were conducted at accelerations as high as 30000 G using mechanical accelerators. Finite element analysis simulations were used to determine impact locations and acceleration magnitude. Wafer level chip scale package components were tested at the board level at accelerations ranging from 10000 to 30000 G. The clearance between the printed circuit board assembly and the fixture are parametrically varied in the investigation to understand the effects of the clearance. Experiments and simulation show interesting results due to dynamic modal interaction. [ABSTRACT FROM PUBLISHER]

This paper deals with the two most used arresters models applied in digital simulations with the Alternative Transients Program, the conventional, and IEEE models. It presents a model analysis and parameter adjustment procedures to the conventional model. It also presents an application to both models of different types of current and voltage surges and even power frequency voltage, with a comparison of the results obtained with both models and with typical manufacturer data. While adjustment of the IEEE model was difficult and laborious, the conventional model presented a straightforward procedure. The results obtained show that there is a close agreement between the two models when the surge front time is above 1/2\ \mus. The conventional model always presents higher values for the limiting and residual voltages, and better agreement with the typical manufacturer data. Thus, the conventional model presents the advantages of simplicity and more conservative results. [ABSTRACT FROM PUBLISHER]

This paper presents: 1) a novel method for accurate high-frequency modeling of dry-type transformer windings based on magnetic and electric field simulations for parameter extraction of the detailed equivalent circuit of the entire winding system; 2) a method for fast and accurate transient solution of the circuit differential equations that describe the voltage distribution over the winding system; 3) an efficient, cheap, and nondestructive low-voltage measurement system based on a self-developed lightning-impulse generator; and 4) verification of the simulation results by comparison with measurement. [ABSTRACT FROM AUTHOR]

This paper addresses the performance of various lightning rod tips: pointed, concave, blunt, flat and conical for lightning air terminal (LAT). To observe the behaviour of the various lightning rod tips, laboratory examination was conducted under two conditions, i.e. corona emission pattern under quasi-static electric field and lightning impulse testing-with and without pre-ionization. The data obtained from the corona emissions were correlated to the surface sharpness area of the tip. Using dimensional analysis, it can be concluded there is strong evidence that increased surface sharpness can lead to an increase in the corona discharge current. In addition, an impulse test was conducted to determine the performance of the LATs with different tip types and sizes. Using the individual and competitive test, it was found that the blunt LAT is the most recommended receptor. [ABSTRACT FROM AUTHOR]

Research on the attachment processes in competition tests can provide insights into the influencing factors involved in the selection process that determines the lightning strike point. In this paper, a series of competition tests with a rod–rod gap configuration are designed and carried out. The test results indicate that the strike mechanism is decided by two discharge processes, namely the free development of the downward-propagating discharge and the interception process of the upward and downward discharges. If the first process prevails, the strike probabilities for different grounded rods will tend to be equal. For the second process, the strike probabilities reflect the different performances of the grounded rods for intercepting downward discharges. As the scale of the discharge gap increases, the development of the downward leader becomes more and more dominant in selecting the strike point. In natural lightning strikes, the scale of the downward leader is normally more than 90% of the discharge gap, hence the protective effect of lightning rods with different tips will not be significant for low rod heights and small lightning currents. To reflect the effect of the downward leader development on the choice of the strike point, a minimum discharge air gap of 10 m is suggested. [ABSTRACT FROM PUBLISHER]

The new IEC 60060-1 standard establishes the k-factor function to determine the test voltage value of lightning impulses with superimposed oscillations, but no rule is given to determine experimental k-factor values. Testing methods, testing setups, and formulas to determine k-factor values are some crucial issues to obtain good results. This paper describes the two procedures used in the investigation funded by the European community and referenced in the Annex D of the last edition of IEC 60060-1 standard to determine experimental k-factor for air gaps, one for nonhomogenous fields and other for quasihomogenous fields. Both procedures were implemented using a setup with only 1 generator and a setup with 2 generators. Compatibility of new experimental k-factor values determined for air gaps up to 900 kV in quasihomogenous field with the factor function stated in IEC 60060-1 is shown by means of several examples, but additional examples show a significant discrepancy for air clearances of a sharp rod-plate configuration in the voltage range 250 to 800 kV. [ABSTRACT FROM PUBLISHER]

This paper designs and experimentally demonstrates an electronic hardware architecture to measure impulse signals without resorting to high-speed analog-to-digital converters (ADCs). The proposed architecture is based on a frequency-domain approach. It consists of multiple channels to down-convert the input signal, each of which obtains a small portion of the input's spectrum. Overlapping bands are designated in between every two adjacent channels, so that multiple narrow-band outcomes can be accurately merged to construct the entire spectrum through postprocessing. The resultant complex-valued spectrum is equivalent to that where the impulses are directly measured in the time domain. The architecture in this paper resembles traditional superheterodyne receivers, and hence, its circuit implementation is simple and robust and has low cost. In our circuit implementation, all the components involved (like oscillators and mixers) are commercially available and have low costs. The circuit is tested by two types of input impulses, both having spectra centered at 2.1 GHz. The input signals' spectra (including both magnitude and phase) obtained by our circuit show excellent agreement with the data measured by a 40-GHz oscilloscope. When the input signal-to-noise ratio is as low as 2 dB, the output of our frequency-domain approach is equivalent to that of a 4-b high-speed ADC. [ABSTRACT FROM AUTHOR]

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This paper presents a numerical method, combined the finite element method in the spatial domain with the finite difference time domain, to calculate the transient impulse response of grounding systems considering the ionization phenomenon. In this numerical method, space-time variable soil resistivity is used to simulate the soil ionization phenomenon where soil resistivity is controlled according to its relationship with the local instantaneous value of the electric field and no a priori hypothesis on the geometrical shape of the ionized region around the electrodes is necessary. Based on the widely accepted principle of dimensional similarity, this paper makes simulated experimental investigations on the impulse-current dispersal regularity of grounding electrodes with various structures. The proposed numerical scheme is validated by comparing computed results with experimental results and simulation results in literature. Based on the measurement and simulation results, the impulse response regularity of grounding electrodes is discussed and the effect of ionization on human and installations safety is reported. [ABSTRACT FROM AUTHOR]

Abstract: This paper presents the design and testing of coaxial D-dot probes with three different designs, namely, totally closed, totally open and semi-open designs. The latter design gives a good response and has an easy-access assembly for fixing and replacing the surge arresters (SA) under test. Simultaneous measurements of residual voltage for 9-kV SA are conducted by the designed probes, and resistive and universal dividers (RD and MRCD). The divider compensation principle is also introduced and implemented for both dividers. Both perfectly compensated dividers and the designed D-dot probes have an error of about 2.5% in the SA residual voltage due to the unavoidable resistance of connecting leads. SA residual voltages measured by uncompensated short MCRD divider give good agreement with that measured by the D-dot probe. The former has small inductive overshoot which can be neglected as the residual voltage crests before the discharge current by a few microseconds. [Copyright &y& Elsevier]

Using the new definitions and analysis specified in the 2010 version of the IEC standards to calculate impulse parameters, this paper investigates the measurement errors and uncertainties of high-voltage impulse dividers due to their nonideal step response using the convolution method. Measured step responses of three different dividers and a range of practical impulse waveforms were used in the calculations. The obtained results indicate, for the first time, that the uncertainty contribution of a nonideal step response can be estimated with sufficient accuracy for the purpose of measuring practical impulse waveforms. [ABSTRACT FROM AUTHOR]

Because of the contact material's evaporation and ejection of some metal particles out of the contact gap during the flow of the vacuum arc, the contact surface may exhibit some erosion after each operation of vacuum circuit breakers. In this paper, the insulation properties were investigated for vacuum interrupters with the rated voltage of about 10-kV operating voltage after short-circuit current interruption of more than 10 kA of 50-Hz current. The vacuum interrupter contacts were opened at either a current-zero point or an ac current peak. The latter involves greater arc energy at the short gap length compared with the former. After such interrupting duty, the V\!-t characteristics were measured with the lightning impulse and rectangular impulse voltages as a function of polarity relative to that of the interrupting current. When the contact was opened at the current peak, the insulation properties deteriorated substantially compared with those of the new interrupter, and the polarity of the applied impulse voltage relative to that of the interrupting current has considerable effect. [ABSTRACT FROM AUTHOR]

We propose a new method for the measurement of (group) delay from the radio-frequency (RF) input to the intermediate-frequency (IF) output of a mixer or a receiver. The method is particularly convenient for measuring the change in group delay with the local-oscillator (LO) tuning frequency of the receiver since the method does not require access to, or even knowledge of, the LO signal. The method employs a calibrated comb (impulse) generator. Other required equipment is limited to a reference signal generator and a digitizer of modest bandwidth, allowing the measurement to rely on a low-frequency generator and an oscilloscope. Simulated and measured data are presented to verify the approach. [ABSTRACT FROM PUBLISHER]

The paper analyzes the test setup required by the International Electrotechnical Commission (IEC) 61000-4-4 to evaluate the immunity of electronic equipment to electrical fast transients (EFT5), and proposes an electrical model of the capacitive coupling clamp, which is employed to add disturbances to nominal signals. The study points out limits on accuracy of this model, and shows how it can be fruitfully employed to predict the interference waveform affecting nominal system signals through computer simulations [ABSTRACT FROM AUTHOR]