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The effect of doping with holmium (Ho) and erbium (Er) rare-earth elements (REE) on the main parameters and characteristics of photocells based on p-GaSe/n-InSe heterostructures has been experimentally studied. Photo-electromotive force measurements were performed for undoped and rare-earth doped samples and obtained results comparatively analyzed. The light characteristic of the samples shows that significant improvement are observed in the rare-earth doped crystals. The possibility of targeted control, as well as increasing their reproducibility and stability by changing the content of the introduced impurity (NREE), is shown. The optimal situation is provided by alloying Er with NREE≈10−1 at.%. [ABSTRACT FROM AUTHOR]

The paper reveals the influence of Li, B and the composition of metal contacts on the processes of resistive switching in memristive structures M/NC/D/M. After field exposure in structures Cu/(Co50Fe50)x(LiNbO3)100–x/s-LiNbO3/Cu/sitall, Cu/(Co50Fe50)x(LiNbO3)100–x/d-LiNbO3/Cu/sitall and Cu/(Co40Fe40B20)x(SiO2)100–x/d LiNbO3/Cu/sitall at x < 13 was detected a residual voltage (up to 16 mV) due to the electromigration of Li ions, that leading to a "reversible" type of VAC hysteresis and instability of the time dependencies of induced resistive states. In the structures of Cu/(Co40Fe40B20)x(LiNbO3)100–x/s-LiNbO3/Cu/sitall, Cr/Cu/Cr/(Co40Fe40B20)x(LiNbO3)100–x/s-LiNbO3/Cr/Cu/Cr/sitall containing B, the residual voltage is reduced by formation of chemical compounds B with percolated Li atoms. When limiting the electromigration of Li ions, the main mechanism of resistive switching is the processes of electromigration of oxygen vacancies in the dielectric oxide layer. Suppression of residual voltage in the Cr/Cu/Cr/(Co50Fe50)x(LiNbO3)100–x/s-LiNbO3/Cr/Cu/Cr/sitall structure due to the introduction of a Cr buffer layer that does not dissolve Li leads to the absence of bipolar resistive switching in these structures. [ABSTRACT FROM AUTHOR]

The paper reveals the influence of Li, B and the composition of metal contacts on the processes of resistive switching in memristive structures M/NC/D/M. After field exposure in structures Cu/(Co50Fe50)x(LiNbO3)100–x/s-LiNbO3/Cu/sitall, Cu/(Co50Fe50)x(LiNbO3)100–x/d-LiNbO3/Cu/sitall and Cu/(Co40Fe40B20)x(SiO2)100–x/d LiNbO3/Cu/sitall at x < 13 was detected a residual voltage (up to 16 mV) due to the electromigration of Li ions, that leading to a "reversible" type of VAC hysteresis and instability of the time dependencies of induced resistive states. In the structures of Cu/(Co40Fe40B20)x(LiNbO3)100–x/s-LiNbO3/Cu/sitall, Cr/Cu/Cr/(Co40Fe40B20)x(LiNbO3)100–x/s-LiNbO3/Cr/Cu/Cr/sitall containing B, the residual voltage is reduced by formation of chemical compounds B with percolated Li atoms. When limiting the electromigration of Li ions, the main mechanism of resistive switching is the processes of electromigration of oxygen vacancies in the dielectric oxide layer. Suppression of residual voltage in the Cr/Cu/Cr/(Co50Fe50)x(LiNbO3)100–x/s-LiNbO3/Cr/Cu/Cr/sitall structure due to the introduction of a Cr buffer layer that does not dissolve Li leads to the absence of bipolar resistive switching in these structures. [ABSTRACT FROM AUTHOR]

To measure the spatial distribution of the magnetic field, both single Hall sensors and arrays of Hall sensors are used. In most cases, a one-dimensional ruler is sufficient. The finished device is called a measuring carriage. The rest of the article describes the first stage of its creation. This article consists in Hall sensor rejection, during which the sensors operate under extreme operating conditions (with increased electrical and thermal loads). During this so-called accelerated aging, the changes in the residual stress values, temperature coefficients, nonlinearity, and divergence of the sensitivity coefficient were monitored. This study can serve as a methodological guide in determining the selection criteria for Hall sensors for precision measuring systems. The need for aging sensors was shown to stabilize their long-term characteristics. In addition, the process of rejecting sensors according to the parameters of interest is described. [ABSTRACT FROM AUTHOR]

Recycling lithium-ion batteries provides sustainable raw materials. Crushing and separation are necessary for extracting metals, like lithium, from batteries. Crushing a battery carries a risk of fire or explosion. Fully discharging the battery is crucial for safe production. Discharging batteries in a salt solution is a simple and cost-effective large-scale process. However, it is important to note that there is a potential risk of corrosion and loss of battery elements when batteries are immersed in a salt solution. The purpose of this study is to investigate the effectiveness of two distinct methodologies at enhancing the voltage drop of a cylindrical battery when immersed in a salt solution while preventing corrosion. These techniques involve the application of iron and copper accelerators. A 20 wt.% salt water solution was chosen based on the research of several researchers. As the current flows through the metal parts, it encounters electrical resistance and forms an electric circuit with the electrolyte solution. This interaction converts electrical energy into various physical–electrical–electrochemical phenomena, leading to a decrease in battery voltage. Research revealed that the battery can be discharged up to 100% within 4 h without causing corrosion to its components. Another point to note is that if copper conductors are used, it is possible to decrease the battery voltage by around 90% within 8 h. The gap between the copper conductor and the battery had a direct impact on the battery's discharge rate. Reducing the distance significantly increased the discharge rate, as confirmed by experimental evidence. This discharge mechanism was thoroughly described in a schematic, and, to further explain the electrochemical reaction, the Pourbaix diagram was utilized for both the Fe-Na-Cl and Cu-Na-Cl systems. Moreover, our theoretical predictions were validated through a chemical and mineralogical analysis of the precipitates that formed in the solution. [ABSTRACT FROM AUTHOR]

Recycling lithium-ion batteries provides sustainable raw materials. Crushing and separation are necessary for extracting metals, like lithium, from batteries. Crushing a battery carries a risk of fire or explosion. Fully discharging the battery is crucial for safe production. Discharging batteries in a salt solution is a simple and cost-effective large-scale process. However, it is important to note that there is a potential risk of corrosion and loss of battery elements when batteries are immersed in a salt solution. The purpose of this study is to investigate the effectiveness of two distinct methodologies at enhancing the voltage drop of a cylindrical battery when immersed in a salt solution while preventing corrosion. These techniques involve the application of iron and copper accelerators. A 20 wt.% salt water solution was chosen based on the research of several researchers. As the current flows through the metal parts, it encounters electrical resistance and forms an electric circuit with the electrolyte solution. This interaction converts electrical energy into various physical–electrical–electrochemical phenomena, leading to a decrease in battery voltage. Research revealed that the battery can be discharged up to 100% within 4 h without causing corrosion to its components. Another point to note is that if copper conductors are used, it is possible to decrease the battery voltage by around 90% within 8 h. The gap between the copper conductor and the battery had a direct impact on the battery’s discharge rate. Reducing the distance significantly increased the discharge rate, as confirmed by experimental evidence. This discharge mechanism was thoroughly described in a schematic, and, to further explain the electrochemical reaction, the Pourbaix diagram was utilized for both the Fe-Na-Cl and Cu-Na-Cl systems. Moreover, our theoretical predictions were validated through a chemical and mineralogical analysis of the precipitates that formed in the solution.

With the widespread application of permanent magnet synchronous motor (PMSM) drives, the demand for safety and reliability has increased. Inverter open-circuit fault is a frequent and severe failure that requires reliable detection and remedial measures. This paper proposes an open-circuit fault diagnosis technique based on voltage residual analysis that does not require additional voltage sensors. The proposed technique analyzes the characteristics of the reference voltage and the actual output voltage under both healthy and fault conditions. To achieve fast and reliable fault detection, it uses the DC component and second harmonic component in the residual voltage between estimated voltage and controller reference voltage. Once an open-circuit fault is detected, the polarity of the DC component is capable of identifying the fault location. The effectiveness and robustness of the proposed technique are verified through simulations and testing on a triple redundant PMSM under various load and speed conditions. [ABSTRACT FROM AUTHOR]

Users expect reliable operation of the surge arrester during overvoltages, which may originate from a switching process or a lightning discharge. The necessary conditions to guarantee these expectations are: appropriate construction of the surge arrester, its production being maintained in accordance with technical standards, and a positive results of the type test (as well routine and acceptance tests). The recipient, especially when purchasing large quantities of the product, can check the final quality of the product through selective testing of samples from the market in order to find the best supplier. This manuscript specifies the basic parameters of low-voltage (LV) surge arresters of four manufacturers. Basic electrical parameters, i.e. leakage current and varistor voltage ( $\text{U}_{\mathrm {1mA}}$ ) before and after the nominal discharge current ( $\text{I}_{\mathrm {n}}$ ) of $8~\mu \text{s}$ /20 $\mu \text{s}$ , were determined for 10 randomly selected surge arresters of each manufacturer. Moreover one sample of each varistor batches was aged by fifty 8 $\mu \text{s}$ /20 $\mu \text{s}$ current impulses with $\text{I}_{\mathrm {n}}$ . The obtained results of structural analysis indicate that the crystal structure of the varistor materials changes after ageing process, affecting its electrical properties. The proposed research methodology can be employed as a basis for forecasting the stability of the arrester parameters under operating conditions.

Before the disposal of lithium–cobalt batteries and lithium–manganese batteries, they must first be discharged to a voltage no greater than 0.5 V. Above 0.5 V, the batteries will catch alight and explode on being opened. Various methods of battery discharge are considered: self-discharge using a flashlight; and battery immersion in NaCl solutions of concentration 5, 10, or 15 wt %. Discharge in salt solution is associated with electrolysis. This process may be theoretically described by means of the basic principles of chloride electrolysis. The effective concentration of the salt solution in battery discharge is found to be 10 wt %. Graphs showing the discharge of LiMn2O4 and LiCoO2 batteries over time are plotted, for a motionless medium. The discharge time is decreased in reactors where mechanical mixers ensure transient or turbulent motion of the liquid (assessed on the basis of the Reynolds number ReM). By atomic-emission spectrometry, the components formed in the residue after battery discharge are determined. On the basis of the results, mixer parameters for preliminary discharge of lithium–cobalt and lithium–manganese batteries are recommended, such that subsequent battery disposal in industrial conditions poses no environmental risks. [ABSTRACT FROM AUTHOR]

With the widespread application of permanent magnet synchronous motor (PMSM) drives, the demand for safety and reliability has increased. Inverter open-circuit fault is a frequent and severe failure that requires reliable detection and remedial measures. This paper proposes an open-circuit fault diagnosis technique based on voltage residual analysis that does not require additional voltage sensors. The proposed technique analyzes the characteristics of the reference voltage and the actual output voltage under both healthy and fault conditions. To achieve fast and reliable fault detection, it uses the DC component and second harmonic component in the residual voltage between estimated voltage and controller reference voltage. Once an open-circuit fault is detected, the polarity of the DC component is capable of identifying the fault location. The effectiveness and robustness of the proposed technique are verified through simulations and testing on a triple redundant PMSM under various load and speed conditions.

In order to study the strong electromagnetic pulse effect of critically vulnerable equipment in power systems and evaluate the survivability under high-altitude electromagnetic pulses, it is necessary to study the characteristics of the transient response of metal oxide arresters to the high-altitude electromagnetic pulse by experiment. In this paper, an experimental platform for high-altitude electromagnetic pulse conduction current injection for a typical 10 kV metal oxide arrester was set up, and the key parameters such as peak value of overshoot voltage, peak value of residual voltage, action voltage and response time were obtained by the experiment. The results show that: the action voltage of this type of metal oxide arrester is 3.53 times higher than that of its rated voltage; the peak value of overshoot voltage is 2.19 times that of the peak value of residual voltage under lightning impulse current; the peak value of residual voltage is 1.57 times that under lightning impulse; and the response time varies little with the electromagnetic pulse conduction current amplitude, averaging 46.86 nanoseconds under a high-altitude electromagnetic pulse conduction environment. [ABSTRACT FROM AUTHOR]

Inductive oil debris sensors have been widely used in the health monitoring of mechanical equipment. Such sensors are important for fault diagnosis, life prediction, and prevention of catastrophic failures. In this article, the concept that the residual voltage caused by the asymmetry of two incentive coils hinders the improvement of the sensor resolution is theoretically demonstrated for the first time. In order to achieve ultrasensitive detection, a novel two-stage autoasymmetrical compensation circuit (AACC) is introduced into the triple-coil debris sensor to automatically suppress the residual voltage in real time. The experimental results show the successful detection of 70 μm (diameter or D) ferrous particles and 165 μm (D) nonferrous particles in a sensing channel with a diameter of 43 mm. The AACC is verified effectively to maintain the residual voltage at an ultrasmall value even in the presence of environmental fluctuations, and the sensitivity of the sensor using AACC is more than 31 times that of the sensor without AACC. [ABSTRACT FROM AUTHOR]

Based on the triggered lightning technology, this study carried out observational tests regarding the impulses of ground potential rise (GPR) to surge protective devices (SPD), and emphatically analyzed the impulse and damage effects of the initial long continuous current processes of triggered lightning on the SPDs. The results showed that after the triggered lightning currents were injected into grounding grids, the SPDs with rated flow rates were easily damaged under the joint actions of the initial long continuous currents of the lightning and the subsequent return strokes. It was observed that when the energy flowing through the SPDs had accumulated to a certain level, only the initial long continuous current processes had caused damages to the SPDs. The impulse effects on the SPDs were determined to be closely related to the different waveforms of the initial long continuous current processes. For example, when the long continuous current processes were superimposed by the initial continuous current pulses (ICCP), with fast rising edges and large amplitudes, then the energy passing through the SPDs tended to rapidly increase. This was believed to likely be the most critical factor related to the damages to the SPDs during the long continuous current processes. [ABSTRACT FROM AUTHOR]

This paper presents a compensation algorithm with software implementation for eliminating the residual voltage in a resolver. The algorithm provides lower-cost implementation and more significant effects than the existing adopted compensation coils. The paper studies the characteristics of the resolver output signals, which mainly consist of the ideal induced signal, the odd-order harmonic components and the residual voltage. First, the resolver output parameters—amplitude, phase and DC component—are estimated by signal fitting methods when the shaft stops at a certain position. Then, the three parameters are again obtained after the driving shaft rotates 180 degrees with respect to the initial position. Because the induced voltage varies with the shaft rotational angle but the residual voltage does not, the amplitude of the residual voltage is obtained by employing the trigonometric identity of the rotational angles to eliminate the amplitude of the induced signal. The experimental results indicate that the proposed compensation method can effectively eliminate the residual voltage in the induced signal and improve the measurement accuracy of the resolver sensors. [ABSTRACT FROM AUTHOR]

In order to study the strong electromagnetic pulse effect of critically vulnerable equipment in power systems and evaluate the survivability under high-altitude electromagnetic pulses, it is necessary to study the characteristics of the transient response of metal oxide arresters to the high-altitude electromagnetic pulse by experiment. In this paper, an experimental platform for high-altitude electromagnetic pulse conduction current injection for a typical 10 kV metal oxide arrester was set up, and the key parameters such as peak value of overshoot voltage, peak value of residual voltage, action voltage and response time were obtained by the experiment. The results show that: the action voltage of this type of metal oxide arrester is 3.53 times higher than that of its rated voltage; the peak value of overshoot voltage is 2.19 times that of the peak value of residual voltage under lightning impulse current; the peak value of residual voltage is 1.57 times that under lightning impulse; and the response time varies little with the electromagnetic pulse conduction current amplitude, averaging 46.86 nanoseconds under a high-altitude electromagnetic pulse conduction environment.

The article gives a comparative analysis of different types of electricity accumulators. A possibility of using a hybrid electrical energy storage based on accumulator batteries and supercapacitors of high power is substantiated as one of the ways to prevent short-term power failures caused by short circuits in external power supply networks. Simulation models of the high power battery, supercapacitor battery and hybrid storage was constructed to evaluate the efficiency of this method.

Multilevel inverter topologies have been widely used in applications of wide-power range and fault diagnosis of such circuits is becoming more and more important. T-type three-level inverters have advantages in efficiency compared to common neutral-point-clamped inverters. This paper proposes a new diagnosis method of an open-circuit (OC) fault for a T-type three-level inverter. The method is implemented by measuring the phase voltage of the circuit and comparing it with the reference voltage of the circuit to obtain a residual voltage. Firstly, according to the analysis of different current conduction paths of the circuit, the voltage level changes of the circuit bridge voltage and phase voltage in different device open modes are studied. Then, based on the above analysis, a device open-circuit fault diagnosis scheme is proposed based on the residual voltage. Finally, simulation and experimental results show that the proposed method can identify the faulty switch exactly and quickly. [ABSTRACT FROM AUTHOR]

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This paper addresses one of the new and most important issues arising when low-power voltage transformers (LPVTs) are used in power network substations for evaluating, among others, the residual voltage measurement. Conversely to open-triangle inductive instrument transformers, the use of phase voltage transformers for measuring the residual voltage gets challenging due to the very high accuracy required for the three LPVTs. In this paper, a general expression to estimate the residual voltage measurement uncertainty, starting from the LPVTs accuracy, is presented. The effectiveness of the proposed approach is then confirmed with both Monte Carlo simulations and actual measurements on a general three-phase system. [ABSTRACT FROM AUTHOR]

Voltage sag frequency estimation is necessary for understanding the voltage sag severity in power system and offering full information for the interested parties to mitigate voltage sag. The high penetration of wind power in the power system and the uncertainty of the fault distribution raise new challenges to accurate voltage sag frequency estimation. This study presents a systematic voltage sag frequency estimation method, considering the fault distribution density, fault ride‐through (FRT) process of wind turbines during voltage sag and the interval characteristic of voltage sag frequency. First, this study proposes a fault distribution estimation model based on adaptive kernel density. Second, this study proposes a method for calculating the residual voltage and duration of voltage sag during FRT and combines the common distance protection action to analyse the effect on voltage sag by FRT process of wind turbines. Lastly, this study proposes an interval‐valued voltage sag estimation method considering the interval characteristics of fault rate in the power system. IEEE 30‐bus test system is used to verify the proposed method, the estimation results show better performance of the proposed method compared with the typical estimation methods. [ABSTRACT FROM AUTHOR]

• The fuzziness of residual voltage, the correlation of duration and the chaos of occurrence time are proposed. • Three prediction models to predict voltage sag characteristics is proposed. • Fuzzy membership function is used to describe the voltage sag fluctuation of nodes under time-varying conditions. • A evidence theory synthesis formula is proposed to enhance the predictability of duration. • The phase space reconstruction is used to describe the multi-dimensional factors affecting the occurrence of voltage sag. An effective method of assisting utilities and users to avoid the risk of voltage sags is the accurate prediction of voltage sags. This study analyzes the predictability and proposes the prediction models for three characteristics of voltage sags based on measured data. First, this study defines the time series of voltage sag and analyzes the predictability of the residual voltage, duration, and time of occurrence. Second, this study proposes a fuzzy logic prediction model of the residual voltage to address the fuzziness of the residual voltage. Third, this study proposes an evidence theory prediction model of the duration according to the correlation between the residual voltage and duration. Further, this study proposes a chaotic signal prediction model of the occurrence time by reconstructing the phase space of the occurrence time. Finally, the measured voltage sag data from 10 sites are used to analyze and validate the proposed prediction models. [ABSTRACT FROM AUTHOR]

The article considers the influence of opportunities forcing synchronous generator (SG) and a synchronous motor (SM) to provide the required level of the residual voltage at the consumer at short circuits in networks of high voltage. It determines the ability of the equipment to remain in the work during such perturbation by mathematical modeling.

Under the influence of series compensation (SC) capacitance and rated voltage rise, when ultra high voltage (UHV) high SC line occurs inner fault, the short-circuit current through the SC line is greater and the residual voltage across the SC is higher, which cause the electromagnetic transient process excited by high amplitude current and voltage to be more serious in the event of fault occurrence and removal. The security of circuit breaker (CB) equipment is threatened, which make it need further research on the characteristics and put forward some effective solutions. In this study, the characteristics of macroscopic statistical distribution of peak value via short-circuit current of transient recovery voltage (TRV) across CB fracture during switching after short-circuit current zero crossing for UHV high SC line are put forward, and also of the microscopic characterization parameter of waveform rise rate and peak value time. It shows that the TRV switching capability of existing UHV CBs can not cover all the fault scenarios of high SC line. Solutions including comprehensive comparison of TRV optimal suppression measures and increase of the UHV CB switching expected TRV test requirements are put forward, which provide feasible technical scheme for CBs reliable switching of UHV high SC line.

Under the influence of series compensation (SC) capacitance and rated voltage rise, when ultra high voltage (UHV) high SC line occurs inner fault, the short-circuit current through the SC line is greater and the residual voltage across the SC is higher, which cause the electromagnetic transient process excited by high amplitude current and voltage to be more serious in the event of fault occurrence and removal. The security of circuit breaker (CB) equipment is threatened, which make it need further research on the characteristics and put forward some effective solutions. In this study, the characteristics of macroscopic statistical distribution of peak value via short-circuit current of transient recovery voltage (TRV) across CB fracture during switching after short-circuit current zero crossing for UHV high SC line are put forward, and also of the microscopic characterization parameter of waveform rise rate and peak value time. It shows that the TRV switching capability of existing UHV CBs can not cover all the fault scenarios of high SC line. Solutions including comprehensive comparison of TRV optimal suppression measures and increase of the UHV CB switching expected TRV test requirements are put forward, which provide feasible technical scheme for CBs reliable switching of UHV high SC line. [ABSTRACT FROM AUTHOR]

Highlights • A novel method to monitor the neutral grounding resistor of unit-connected generators is proposed. • The proposed method uses the third harmonic of neutral and residual voltages to detect the resistor failure. • The proposed technique has been restrained against load variation, step-up transformer saturation and ground faults. • Maloperation of generator stator ground protection due to neutral grounding resistor failure has been resolved. Abstract Neutral grounding resistors are used to control transient overvoltages and overcurrents in power systems. Failure of these critical assets revives many disadvantages of ungrounded and solidly grounded traditional systems. Therefore, monitoring the neutral grounding resistors is necessary. A new continuous monitoring technique is proposed for such a resistor located at the neutral of unit-connected generators. It detects resistor failure by comparing the third harmonic of neutral and residual voltages. This proposed scheme demonstrates reliable operation under various conditions of the system and resistor as observed by PSCAD in conjunction with MATLAB. Further performance validation has been carried out using an industrial generator protection relay as well. In contrast to existing methods, this scheme does not require any additional measurement instruments. Thereby, it is easily retrofitted to installed unit-connected generator protection infrastructures. Moreover, this continuous monitoring technique prevents maloperation of the generator stator ground protection due to the neutral grounding resistor failure. [ABSTRACT FROM AUTHOR]

• Electromagnetic transient model for varistor-based surge protective devices. • Resistive, inductive, and capacitive behavior of varistor-based SPDs. • Residual voltage of SPDs depends significantly on their base configuration. • Excellent simulation results for a wide range of very fast-front impulse currents. • The model can be used for insulation coordination studies and dimensioning of SPDs. This work provides a simplified transient model for low-voltage DIN rail surge protective devices (SPDs), accounting for their resistive, inductive, and capacitive behavior. The time-domain modeling approach is based on impulse current and sinusoidal voltage experiments. The lumped-circuit model is implemented in the ATP-EMTP environment and yields results in satisfactory agreement with the experimentally derived residual voltage and energy absorption of commercially available DIN rail SPDs for single- and three-phase installations. The proposed model can be used for evaluating the protection level and maximum residual voltage of SPDs under standard and non-standard surge currents and can be an effective tool employed in insulation coordination studies of power systems. [ABSTRACT FROM AUTHOR]

Metal oxide surge arrester accurate modeling and its parameter identification are very important for insulation coordination studies, arrester allocation and system reliability. Since quality and reliability of lightning performance studies can be improved with the more efficient representation of the arresters´ dynamic behavior. In this paper, Big Bang – Big Crunch and Hybrid Big Bang – Big Crunch optimization algorithms are used to selects optimum surge arrester model equivalent circuit parameters values, minimizing the error between the simulated peak residual voltage value and this given by the manufacturer.The proposed algorithms are applied to a 63 kV and 230 kV metal oxide surge arrester. The obtained results show that using this method the maximum percentage error is below 1.5 percent.

This article proposes a method for the parameters adjustment of the Matlab Simscape library Surge Arrester block. It is based on building of nonlinear V-I characteristic by approximation of residual voltage and impulse current obtained from manufacturer catalogs. Given parameters of the exponential function are checked by transient simulations under impact of standard current impulses on surge arresters. References 14, figure 1, tables 3.

Lightning overvoltage may affect the signal transmission and damage terminal equipment. In order to solve this problem, the signal system Surge Protection Devices (SPDs) is designed by analyzing the signal transmission characteristic and the design theory of SPDs. The impulse tests are performed on the SPDs using a combined wave generator. Residual voltages and sharing currents are measured and discussed by considering impulse voltages, DC breakdown voltages of downstream SPDs and decoupling resistances. The blind zone of the signal system SPDs is also discussed in detail. In addition, the SPDs are equivalent to a two-port network, and the influence of distributed capacitance of the SPDs on signal transmission is analyzed for the first time through experiments. Cut-off frequency is measured and discussed by considering DC breakdown voltages of downstream SPDs and decoupling resistances. From the two experiments, the results indicate that increasing the decoupling resistance can decrease residual voltage and sharing current, but will reduce the cut-off frequency. Decreasing the DC voltage of downstream SPDs will have a similar effect. So the decoupling resistance and the DC breakdown voltage of downstream SPDs resistance need to be considered carefully in designing signal system SPDs. The sufficient research of signal system SPDs in this paper has a certain reference value in lightning protection. [ABSTRACT FROM AUTHOR]

The object of research is an analytical expression for representing the switching current impulse of a surge arrester. Any current impulse (both lightning and switching) is characterized by such parameters as the virtual front time and the virtual time to halfvalue on the tail. According to the standard IEC 60099-4:2014, switching current impulse has a virtual time to half-value on the tail of roughly twice the virtual front time. This requirement is one of the most problematic places in this task. The existing approaches used to represent lightning current impulses are not suitable in this case, since these impulses have virtual time to half-value on the tail of two and a half times the virtual front time. This problem can be solved with a help of analytical piecewise continuous functions. It is shown how to describe switching current impulses of the surge arresters with a help of analytical piecewise continuous functions. In contrast to other expressions, the resulting expressions for the switching impulse have only one parameter (angular frequency). Instead of approximate calculation, the front time of the resulting impulse is calculated by an analytically exact formula. Hence, the tolerance of virtual front time is equal to zero. The time to half-value on the tail of the resulting impulses is determined with some error that can be reduced by some complication of the original expression. The proposed functions satisfy the requirements of the IEC 60099-4:2014 standard regarding switching current impulses of surge arresters. These functions allow representing current impulses having virtual time to half-value on the tail of roughly twice the virtual front time (30/60 or 45/90 microseconds). In such cases, minimal tolerance of time to half-value on the tail is +3.78 %. Additional study shows that one of proposed functions allows representing current impulses having virtual time to half-value on the tail of two and a half times the virtual front time (8/20 or 4/10 microseconds). Tolerance of time to half-value on the tail for such impulses is 0.55 %. The obtained functions are intended for study of various models of metal-oxide surge arresters on personal computers. [ABSTRACT FROM AUTHOR]

Gas insulated substation generates very fast transient overvoltages (VFTOs) in power systems because of disconnector switching operations. The present design of metal–oxide arrester may not be effective against these VFTs and so the arrester fails to operate under VFTO. At this point, it becomes essential to improve the electrical behaviour of arrester. Some of the possible measures for improving the electrical behaviour of arrester blocks are the procurement of higher‐voltage gradient, reduction of arrester capacitive effect and reduction in the time lag between residual voltage and current surge. With this background, the microstructural and electrical parameters of arrester block are modified by doping scandium trioxide with basic composition and the samples are prepared using different sintering processes. Subsequently, the voltage gradient, capacitance and the time lag are found for the prepared samples. The performance of new arrester blocks are investigated against VFTO and the results are compared with conventional arrester blocks. From that, it is perceived that the new arrester samples have improved parameters and might be used for protection of power system against VFTO. [ABSTRACT FROM AUTHOR]

Operating experience shows that residual DC voltage remains in GIS bus bar for a long time after opening of disconnectors. This DC voltage will not only cause accumulation of charges and contaminants on the insulator surface, but will also easily lead to motion of free metallic particles in SF6 gas gap, weakening the insulation ability of GIS. At the time of disconnectors reclosing, impulse voltage could be generated in the bus bar and superimpose on the pre-existing DC voltage. As a result, GIS will be under combined voltage of DC and impulse. This paper experimentally studies the insulation characteristics of GIS under combined voltage of DC and lightning impulse. It is found that, for non-contaminated insulators, when DC and LI voltage are of the same polarity, flashover voltage under combined voltage is nearly the same as the flashover voltage under LI alone. However, when they are of the opposite polarity, flashover voltage decreases with increasing DC voltage. In cases there are metallic particle or powder around insulator, pre-stressed DC voltage will cause adhesion of contaminants on the insulator surface and lead to decrease of flashover voltage. Specially, for the particle-contaminated insulator, it is found that the surface charge accumulation caused by DC voltage will have big influence on the flashover voltage, and the most critical condition is when DC and LI voltage are of the opposite polarity. In addition, the breakdown characteristics of SF6 gas gap with free metallic particle are investigated. It is found that under pre-stressed DC voltage, particle will do standing motion or bouncing motion. And breakdown voltage becomes lowest when particle is doing standing motion. The results of the experiments show that residual DC voltage in GIS could deteriorate its insulation ability and the combined voltage of DC and impulse is found to be a critical condition for GIS insulation. Moreover, the combined voltage is shown to be more sensitive to detect some insulation defects in GIS than applying impulse voltage alone, especially for free metallic particles, which are commonly found in GIS but up to now no effective detection method is proposed. Therefore combined voltage of DC and impulse could be considered to serve as a supplement of field test for GIS. [ABSTRACT FROM PUBLISHER]

The model of surge arrester, which consists of two nonlinear resistors, connected with each other via two inductive and a resistive element is studied. To determine the model parameters are only required by the data given in the catalogs of surge arresters manufacturers. Until now, in the simulation of surge arresters insufficiently investigated the effect of currents typical for lightning surges. It is shown that the model of surge arrester can be investigated by comparing the results of computer simulation with the data given in the catalogs of surge arresters. The study will use the following data, specific both switching and lightning surges: the residual voltage at switching impulse current, the residual voltage at lightning impulse current, as well as the residual voltage at steep current pulse. Residual voltages corresponding to the 250-2000 A standard switching current pulses, 1.5-20.0 kA standard lightning current pulses and 10.0 kA steep current pulses were defined using Micro-Cap model of surge arrester. Residual voltages obtained in the simulation were compared with the corresponding values given in catalogs of surge arresters. It is shown that the smallest error takes place under the influence of lightning current pulses on the model of surge arrester. The model of surge arrester in Micro-Cap program allows high accuracy determination of the residual voltage on the surge arrester during the flow of discharge pulses, which are typical for lightning surges. The model also allows to calculate the transients during the flow of the lightning currents, which are composed with several successive pulses, which can pose a significant danger to the surge arresters. The results of the research can specify the parameters of substation protection against different overvoltages and, thus, reduce economic losses due to possible faults. [ABSTRACT FROM AUTHOR]

• The single-phase reclosing technique should not be used in half-wavelength transmission systems. • The residual voltage of half wavelength transmission system can be used to determine the existence of faults. • The frequency difference of residual voltage can be used to determine the existence of faults. • We propose a complete and feasible three-phase adaptive reclosure scheme for half wavelength transmission system. UHV AC transmission lines use adaptive reclosure technology not only to avoid reclosing in the permanent faults, but also effectively prevent the emergence of reclosing overvoltage, adaptive reclosure is of great significance, and its technical principle is based on the study and judgment of the existence of the fault. The reactive power of half-wavelength transmission lines along the line was self-balanced, no shunt reactor equipment, there is no "beat frequency" phenomenon, and very little information is available after the three-phase trip. In this paper, we analyze the fault traveling wave's frequency characteristics and identify the fault's characteristics based on the residual voltage frequency difference of the line after the three-phase trip. After the disappearance of the line fault, the stable frequency difference obtained by CVT reflects the entire length of the line, which is not affected by the system boundary conditions and can complete the reliable identification of the disappearance of the line fault. The two-terminal criterion is given for the short-line dead zone problem, and then a three-phase adaptive reclosure scheme for half-wavelength transmission lines based on the frequency difference to identify fault disappearance is proposed. Extensive RTDS digital-analog hybrid tests show that the method is correct and robust. [ABSTRACT FROM AUTHOR]

• Complete VFTO(s) generation and measurement system based on (MPC) and (TLT) technologies. • Five commercial ZnO varistors of the same reference were used in the characterization. • The influence of the applied overvoltage front time on the capacitive effect of the varistor is confirmed. To study the behavior of low voltage ZnO varistors against Very Fast Transient Overvoltage (VFTO), the authors have developed a complete VFTO(s) generation and measurement system based on magnetic pulse compression (MPC) and Transmission Line Transformer (TLT). This system has an output voltage of 24 kV, rise time of 32 ns, and a bandwidth of 10 MHz. The measurement system comprises a damped resistive voltage divider with an impedance of 1000 MΩ and a maximum bandwidth of 10 MHz. The experiment was performed with five commercial zinc oxide varistors with a nominal voltage of 150 V, each one was subjected to VFTO-type voltage pulses and, by Analysis of Variance (ANOVA), a single varistor was selected to perform the case study. This work presents an experimental methodology to observe the response of low voltage ZnO varistors against VFTO. This response is the delay of the residual voltage to the applied discharge current and indicates the poor performance of these devices against VFTOs. Our methodological proposal consists of a series of laboratory tests that will allow manufacturers and consumers to take corrective measures in case of malfunction, damage of the varistor material, or permanent degradation of the device. [ABSTRACT FROM AUTHOR]

Surge Protective Devices (SPDs) are widely applied to protect the low-voltage equipment against the surges from direct lightning strikes or the lightning-induced effect. To ensure the protection effect, the users should not only consider the performance and quality of the SPDs themselves, but also the coordination between SPDs and between SPD and the protected equipment. In practice, there may be SPDs with different characteristics from many manufacturers on the same line. One SPD is installed by the contractor in charge of electrical installation and then various panel boards are used in the installation made by various panel builders. All of them may use different brands of SPDs. So it is difficult to evaluate the coordination effect between those SPDs and between SPD and the protected equipment by theoretical analysis. A solution would be to perform the coordination test. This paper provided an investigation on the proposed coordination test method for different configurations with various loads, various cable lengths, various cable enclosures and various surge waveforms through experiments in the laboratory. The sharing current and residual voltage of two cascaded SPDs were measured and discussed. The proposed coordination test method was verified to be informative for achieving successful coordination between SPDs and between SPD and the protected equipment. [ABSTRACT FROM AUTHOR]

Impulse voltage testing is generally carried out for assessing the insulation strength of power equipment using standard impulse voltage waveforms in high-voltage laboratory. However, in actual field, the power equipment experiences standard and non-standard lightning impulse voltages. The main objective of this work is to analyse the voltage stress on surge arresters under standard and non-standard lightning impulse waveforms. Surge arrester models are developed in matlab (The MathWorks, Inc., Natick, Massachusetts, United States), and residual voltage test results are compared with manufacturer data for validation. Impulse voltage test is performed on the Institute of Electrical and Electronics Engineers surge arrester model using standard and non-standard lightning impulse voltage waveforms. The obtained test results showed that non-standard impulses have the potential to develop higher voltage stress and hence pose a high risk to surge arresters. However, results of this study provide the basis for further laboratory-based investigation considering a wide variety of impulse voltage waveforms representing the real lightning overvoltages. The test results will contribute to identify the need for modifying existing test standards or introducing new standards for impulse testing of surge arrester. Copyright © 2015 John Wiley & Sons, Ltd. [ABSTRACT FROM AUTHOR]

The characteristics of the residual voltage of a surge protective device (SPD) connected to an overhead distribution line due to nearby natural cloud-to-ground lightning and to rocket-triggered lightning are analyzed in this paper. The residual voltage of the SPD is found to be closely related to the ground potential rise at the grounding terminal of the SPD. For natural lightning occurring 1.8 km to 10.5 km away from the SPD, the ground potential rise (GPR) is too small to influence the residual voltage of SPD. For rocket-triggered lightning with a 40-m distance between the lightning channel and the SPD, the residual voltage of SPD is primarily determined by the voltage induced in the distribution line for return stroke and large M-components process, whereas the influence of the GPR becomes strong in the minor M-components stage. For a 5-m distance between the lightning channel and the SPD, the residual voltage of SPD originates primarily from the GPR during the entire flash, exhibiting the characteristics of reversed polarity. The duration of SPD's residual voltage may be up to the order of milliseconds due to the GPR in the case of the large M-components and a long continuing current process, which may cause damage to the SPD. [ABSTRACT FROM AUTHOR]

Reacceleration is a method of automatically restarting motors after an unexpected deacceleration caused by system voltage events such as dips, outages, or bus transfers. Reacceleration schemes are designed to minimize process disruptions by rapid detection of supply loss, recovery/ monitoring of acceptable transient torque limits, and then automatic reclosure of the motor contactors. Depending on the connected load and minimum available fault current, the reacceleration may be “instantaneous” or a staged event designed to assure that the bus voltage is maintained at an acceptable level during the process restart. Poor coordination of the reacceleration process may cause further system outages if the nominal bus voltage drops below tolerable levels. Special consideration is required to prioritize loads, to maintain production, to prevent lifting of safety valves, and to avert equipment damage. Various processes differ in their ability to withstand temporary outages, from milliseconds (ms) to several seconds. Today's protection and control intelligent electronic devices (IEDs) provide settings, dedicated measurement, and timing circuits to allow these variances to be preprogrammed and activated based on outage duration and magnitude. Short-time outages within millisecond range combined with electrically held contactors provide the least complex situations for enabling a reacceleration system. More complex situations arise when motors are still decelerating and when the supply is restored, especially if the contactors were maintained closed during the outage. Certain more advanced IEDs also provide multiple reacceleration schemes that are automatically deployed based on longer outages—typically up to 30 min. [ABSTRACT FROM AUTHOR]

Transferring motor loads from one bus to another bus, due to a source disconnection from a main–tie–main arrangement, is not a trivial action. The transfer is dependent on detection of breakers' status, switch positions, and accurate measurements of line and bus voltages. The mechanism of transferring loads from one bus to the other imposes a number of requirements for the relay controlling the closing of the tie-breaker. The main requirement in this process is to accurately measure both the bus voltage from the “healthy” source and the decaying voltage from the bus disconnected from its supplying source. This is done to assure accurate and smooth transition of the motors to the healthy source. To perform accurate ac measurements, many protective devices are built to track the power system frequency from one voltage source. However, when the source for the frequency tracking is lost, the accuracy of the measurements associated with the voltages and currents from the healthy source is jeopardized. In such conditions, the relay may declare an absence of healthy bus voltage and could prematurely issue a close command to the tie-breaker, while the magnitudes of both bus voltages are still high and out of phase. Closing of the tie-breaker under such conditions can stress the motors and damage them due to a high torque. This paper reveals a method for accurate voltage measurement and shows a number of tests proving that inaccurate voltage measurement, due to decaying frequency in existing relay designs, could cause incorrect tie-breaker closure during transfer operations. Both scenarios of decaying voltage used for frequency tracking and decaying voltage from the other bus are explored. This paper discusses alternative methods for accurate bus voltage measurements during frequency decay of the reference voltage and makes recommendations for optimal relay performance. [ABSTRACT FROM AUTHOR]

In the past few years, grid‐code requirements for grid‐connected photovoltaic power plants have experienced a continuous evolution in different countries to ensure a reliable power system operation as the level of renewable energy penetration increases to high levels. According to several European grid‐codes, PV power plants must be able to ride through specific and severe disturbances without disconnections. Under this new framework, the present study analyses intensive power quality surveys carried out from 2008 to 2011 in three different Spanish PV power plants: a fixed array installation with 4 MW PV power capacity, a PV power plant including dual axis–trackers with 1 MW PV power capacity, and one more fixed array PV power plant with 5 MW PV power capacity. Voltage dips and supply interruptions have been collected, discussing several methods to characterise the monitored disturbances and to compare these events to current Grid‐Code requirements. Furthermore, the time interval around the residual voltage is proposed and defined by the authors as an additional parameter to provide a complete characterisation of the severity of the disturbances. Results from both characterisations of collected data and comparison with current requirements are also included in the study. [ABSTRACT FROM AUTHOR]

Structure, texture, chemical purity, and other characteristics of superconductive niobium coatings prepared via electrochemical deposition onto nickel and copper substrates in (LiF + NaF + KF) + 5 wt % KNbF molten salt are studied. It is shown that, when depositing the coatings onto nickel, the intermediate layer of NiNb and NiNb intermetallides is formed at the substrate-coating interface, which inhibits the diffusion of nickel in niobium. The nickel concentration in niobium coatings above this layer is (2-7) × 10 wt %. In coatings deposited onto the copper substrate the copper content does not exceed 1.5 × 10 wt %, and from the viewpoint of the amount of impurities, niobium is considered as a high purity metal. The dynamics of structure modifications in niobium coatings and changes in microdeformations and dislocation density in the deposited metal are explored depending on the current density at the cathode. [ABSTRACT FROM AUTHOR]

It is well known that metal–oxide arresters (MOAs) do not have the capability of protecting the equipment in extra-high voltage networks, when they face the threats from very fast transients (VFTs). This “inaction” on the part of MOA is mainly brought by stray capacitance, which not only delays the conduction of MOA under VFTs but also brings a nonuniform voltage distribution across its structure and thereby impacts its life, especially, that of its top unit. This phenomenon prompts an urgent take on the factors that threaten the functioning of MOA under VFTs. After performing a thorough review of the studies made earlier, this study focuses on the further improvements required. This paper mainly deals with the accurate calculation of stray capacitance, its adverse impacts on MOA during its conduction phase, voltage distribution across the arrester with the aid of a finite-element method (FEM) and the Electromagnetic Transient Program (EMTP), and, finally, it explores the modifications required to get adequate protection for the equipment exposed to VFTs. [ABSTRACT FROM AUTHOR]

Voltages induced on a 1300-m overhead power line by 51 return strokes in a thunderstorm process in Guangzhou Field Experiment Site during the summer of 2008 have been measured. As to a group of surge protective devices (SPDs) were installed at the end of the overhead power line, the peak values of induced voltages were all below 1 kV, and most of induced voltage waveforms show typical residual voltages. The interval time of adjacent return strokes ranged from 14.0 to 185.6 ms. The peak values of induced voltages at the SPD site were obviously under attenuation compared to that at the household site. The lightning location data indicate that the induced voltage might be of either positive or of negative polarity depending on the location of the lightning strike points. The peak value of induced voltage tends to saturate when the ratio of peak value of return stroke current to distance from the stroke location to the measuring point exceeds 4 kA/km. [ABSTRACT FROM PUBLISHER]