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Copyright of Energy Policy Journal / Polityka Energetyczna is the property of Mineral & Energy Economy Research Institute of the Polish Academy of Sciences and its content may not be copied or emailed to multiple sites or posted to a listserv without the copyright holder's express written permission. However, users may print, download, or email articles for individual use. This abstract may be abridged. No warranty is given about the accuracy of the copy. Users should refer to the original published version of the material for the full abstract. (Copyright applies to all Abstracts.)

Lightning transient response analysis is the key to determining the lightning resistance level of transmission lines and the performance of lightning protection measures. This paper proposes a distributed modelling method for a typical 110 kV transmission tower and further analyses the lightning transient response. The refined modelling of the nominal height part of the tower is carried out. Then the influence of the refined modelling on the refraction and reflection process of the lightning wave propagation is investigated. Based on the distributed tower model, the impact of the foot distance and the equivalent radius of the main body cylinder on the top overvoltage is studied. Field experiments indicate that the proposed distributed tower model can effectively reflect the transient lightning wave process. Moreover, it can provide technical support for the lightning resistance level of transmission lines and the lightning protection of narrow base towers. [ABSTRACT FROM AUTHOR]

A protection scheme is proposed using alienation method derived from coherence model which is a backup protection method for the differential overcurrent protection of synchronous generators. This scheme which is realized by the computational technique based on the alienation coefficients estimated for generator voltage and current signals is considered to be mounted beside the main differential protection system, which operates in the cases that differential protection is unable to detect the internal faults. This novel protection algorithm operates by adjusting the alienation settings of the suggested relay that sends the trip signal to the three‐phase circuit breaker of the protected generator. In the proposed method, fault occurrences can be determined regardless of variations of terminal voltage and current in different working states of synchronous generator. This is done by designing new quadratic‐tripping characteristics based on alienation limits for the electrical signals. To demonstrate the proposed method, a motor‐synchronous generator set with built instrument transformers, for measuring voltage and current data at the generator terminals, are used. Extensive experimental investigations validate the functionality of this novel protection scheme under different abnormal, unbalance and operating conditions for the generator under test. [ABSTRACT FROM AUTHOR]

Abstract The main protection equipment in radial distribution networks are non‐directional overcurrent relays (NDOCR) and fuses which are coordinated using the conventional protection coordination method. By installing distributed generations (DGs) in the network, reverse short‐circuit currents (SCC), injected from DGs, can lead to false tripping of NDOCRs and false melting of fuses. In the previous studies, some methods have been proposed to overcome these issues using directional overcurrent relays, fault current limiter, and adaptive methods that relay on communication. The present paper proposes a new coordination method to prevent these issues without the need for installing a new equipment, by proposing a new set of selectivity constraints. Here, selectivity between equipment is established, and false tripping and false melting issues are mitigated. The coordination of protection equipment according to the proposed method requires the use of optimization algorithms, and therefore, the proposed method is formulated as a mixed‐integer linear programming method to take advantage of mathematical optimization algorithms. The proposed coordination method is applied to a real distribution network and the results indicate the high efficiency of the proposed method in dealing with false relay tripping and fuse melting issues. [ABSTRACT FROM AUTHOR]

We report on the experimental investigation of the photoconductively switched gas-filled spark gap. When the laser intensity of a femtosecond laser is high enough (around 1018 W m-2), a plasma can be created that spans the complete distance between the electrodes. The gas-filled spark gap is then closed on a femtosecond time scale, similar to photoconductive switching of a semiconductor switch. Stochastic breakdown processes, such as avalanche and streamer formation that cause the breakdown in laser triggered spark gaps, are passed over, which results in faster rise time and less jitter. Measurements of the switched pulses as a function of laser energy were performed in a 1-mm gap at an applied voltage of 4.5 kV. A clear transition from triggering to switching was measured with increased laser energy. Measurements of the output pulses with the gap filled with nitrogen at 1 atm showed results very similar to measurements in air in the same gap. In the switching regime, the amplitude of the switched pulse did not depend strongly on the laser energy. Measurements at lower applied voltages but with the same gap distance showed that it was possible to switch voltages as low as 10% of the self-breakdown voltage. At low applied voltages, a significant difference between the applied voltage and the output voltage is measured. A possible explanation is given based on the dynamic behavior of the laser-created plasma. The measured rise time and jitter of the switched pulses were both below the resolution of the measurement equipment, i.e., better than 100 and 15 ps, respectively. [ABSTRACT FROM AUTHOR]

We provide “best practices” for single-event transient (SET) mitigation using electrostatic discharge (ESD) protection techniques. We investigate the correlation between SET suppression and RF performance when ESD protection circuits for SET mitigation are combined with various RF switches. The three different single-pole single-throw (SPST) switch configurations (conventional design, floating body, and floating body/n-well) were implemented to provide insight on how to best apply dc ESD protection techniques for also achieving robust SET mitigation. Based on two-photon absorption laser experiments and RF measurements, a conventional SPST switch configuration shows relatively poor RF performance but is effective for SET mitigation due to the SET discharge current path provided by ESD protection circuit. On the other hand, the combination of the SPST switch and the ESD circuit, which exhibits the best RF performance among the three configurations, is relatively vulnerable to SETs. Based on these results, strategies and methodologies for ESD protection techniques to effectively mitigate SET are proposed. [ABSTRACT FROM AUTHOR]

Silicon solar cells with graphene have commonly some drawbacks in assuming Schottky junction configurations, small active areas, carrier’s recombination at interface of graphene/silicon junction, high cost, and complex manufacture processes. We report a new silicon thin-film solar cell structure with graphene, gold (Au) nanograting, and back silver (Ag) contact, which has advantages of simple fabrication method, no graphene/silicon Schottky junction complexity, high absorption, and high short circuit current density. We simulate the proposed specific graphene–silicon solar cell layer assembly by using the 2-D FEM under the standard global AM1.5 spectrum conditions. The generation of strong magnetic resonance field arises due to graphene sheet covered on top of gold nanograting and specific dielectric spacer thickness and slit period and leads to increase absorption and transport of charge carriers in p-i-n silicon layer sandwiched between dielectric spacer and back contact. We report that absorption improvement can be simply tuned by adjusting few geometric parameters of proposed device and maximum absorption is achieved up to 80% in near-infrared wavelength ranges. As an outcome, maximum short circuit current density ($J_{\mathrm {sc}}$) of 32 mA/cm2, open-circuit voltage ($V_{\mathrm {oc}}$) of 0.45 V, and calculated power conversion efficiency of 10.5% are achieved without chemical doping of graphene. The proposed simple structure configuration of silicon thin-film solar cell with graphene on top offers flexible tuneability, high short circuit current values, and increased optical absorption that are beneficial for practical fabrication and industrial applications. [ABSTRACT FROM AUTHOR]

This study presents an analytical and experimental method for detecting internal turn-to-turn short circuits both in the rotor or in the stator in salient pole synchronous generator machines (SSGM) connected to local power grid. Two main measurements are proposed to confirm or discard these electric faults: external magnetic field and external housing vibrations (EHV). In the event of a short-circuit winding fault, a correlation between external magnetic field and EHV is done to reinforce the diagnosis. Furthermore, the electric power injection dependence is analyzed and a noninvasive technique is proposed to determine the state of the SSGM whatever its load. Thus, it is shown that only noninvasive and online equipment can be used to diagnose SSGM. A diagnostic tool has been developed to show the viability of an operative wireless monitoring system on a 76-MW SSGM in an industrial environment. [ABSTRACT FROM AUTHOR]

This paper presents a low-jitter, low-trigger-threshold, high-dielectric-constant ceramic, plasma-triggered gas switch developed for pulsed power generators. We also discuss the principles behind the switch and the experiments and numerical calculations used. The electron emission and surface flashover in the trigger structure are used to create the initial plasma for switch breakdown. The experimental results show that the switch is triggered stably with a negative pulse of −50 kV peak and has a breakdown delay time jitter of 2–3 ns. In this jitter performance, the switch has a switch coefficient below 20%, and a peak current-carrying ability of at least ±5 kA in dry air at atmospheric pressure. The switch can also be reliably triggered with a switch coefficient of 49.7% and an over-voltage ratio of only 0.16 in dry air. [ABSTRACT FROM AUTHOR]

The installation of photovoltaic (PV) systems is gaining great attention due to the matured PV technology and the lowered price of PV modules. With an increasing penetration of PV systems, the selectivity of distribution network protection may be affected which results in undesirable de-energisation of loads, damage of network equipment, and reduction of reliability. This study presents a method to preserve the protection coordination considering future PV systems installation with any penetration level and different locations along the distribution feeder. Depending on the accessibility of protection device settings or PV control parameters, the proposed method modifies the existing characteristic curve of overcurrent devices or limits the output current of PV sources, respectively. The proposed strategy does not change the structure of existing distribution network protection system and can also be implemented in the old and non-programmable relays. Meanwhile, it does not need the communication links. The merits of the proposed method are demonstrated through several case studies using the Isfahan distribution network. [ABSTRACT FROM AUTHOR]

In oil transmission station, the operating condition (OC) of an oil pump unit sometimes switches accordingly, which will lead to changes in operating parameters. If not taking the switching of OCs into consideration while performing a state evaluation on the pump unit, the accuracy of evaluation would be largely influenced. Hence, in this paper, a self-organization Comprehensive Real-Time State Evaluation Model (self-organization CRTSEM) is proposed based on OC classification and recognition. However, the underlying model CRTSEM is built through incorporating the advantages of Gaussian Mixture Model (GMM) and Fuzzy Comprehensive Evaluation Model (FCEM) first. That is to say, independent state models are established for every state characteristic parameter according to their distribution types (i.e. the Gaussian distribution and logistic regression distribution). Meanwhile, Analytic Hierarchy Process (AHP) is utilized to calculate the weights of state characteristic parameters. Then, the OC classification is determined by the types of oil delivery tasks, and CRTSEMs of different standard OCs are built to constitute the CRTSEM matrix. On the other side, the OC recognition is realized by a self-organization model that is established on the basis of Back Propagation (BP) model. After the self-organization CRTSEM is derived through integration, real-time monitoring data can be inputted for OC recognition. At the end, the current state of the pump unit can be evaluated by using the right CRTSEM. The case study manifests that the proposed self-organization CRTSEM can provide reasonable and accurate state evaluation results for the pump unit. Besides, the assumption that the switching of OCs will influence the results of state evaluation is also verified. [ABSTRACT FROM AUTHOR]

A novel active controlled primary current cutting-off zero-voltage and zero-current switching (ZVZCS) PWM three-level dc-dc converter (TLC) is proposed in this paper. The proposed converter has some attractive advantages. The OFF voltage on the primary switches is only Vin/2 due to the series connected structure. The leading-leg switches can obtain zero-voltage switching (ZVS), and the lagging-leg switches can achieve zero-current switching (ZCS) in a wide load range. Two MOSFETs, referred to as cutting-off MOSFETs, with an ultra-low on-state resistance are used as active controlled primary current cutting-off components, and the added conduction loss can be neglected. The added MOSFETs are switched ON and OFF with ZCS that is irrelevant to the load current. Thus, the auxiliary switching loss can be significantly minimized. In addition, these MOSFETs are not series connected in the circuit loop of the dc input bus bar and the primary switches, which results in a low parasitic inductance. The operation principle and some relevant analyses are provided, and a 6-kW laboratory prototype is built to verify the proposed converter. [ABSTRACT FROM AUTHOR]

This article presents a scalable power-gating scheme approach to reduce leakage power using intermediate poweroff modes. An important limitation in power-gating scheme is its variations with wakeup time during activation mode changes, as is often the case. The authors have proposed a novel power-gating scheme that are accomplished by hierarchical mode activation to reduce worst case delay bound. The system combines the advantages of leakage power reduction and wake up time optimization. The influence of power-gating scheme on circuit performance is studied and concluded that finite power-off modes, scalable modes are important for good performance. Key selection of power-off modes over entire circuit is complex and it is computationally more expensive. To get more accurate modes with finite trade off in wake up time, this new approach gives near-perfect ways of isolating modes from other changes. The complete power-gating scheme system was evaluated on a multiplier logic core as a test sample and also compared against well known power-gating schemes. [ABSTRACT FROM AUTHOR]

This paper presented issues concerning the operation process of electronic safety systems. The particular attention was paid to the issues related to periodic inspections and rationalisation of the readiness index value. The analysis of current reliability and operation models allowed to conclude that a thesis, which also takes into account information obtained from diagnostic subsystems, is right. This approach made it possible to develop a graph of relationships in the system including diagnostic information. [ABSTRACT FROM AUTHOR]

A high-speed earthing switch (HSES) of a gas-insulated switchgear (GIS) performs a secondary role in protecting the power system in the event of an accident. After being interrupted by a circuit breaker (CB), the short-circuit current remaining in the network should be earthed by the HSES. However, as the contacts of the HSES may have been damaged by a pre-arc during the closing operation, the HSES may fail to ground the short-circuit current. To successfully ground the short-circuit current, the contacts of the HSES must be protected from damage by the pre-arc. Thus, minimizing the pre-arcing time is required to step up the making performance. This paper analyzes the making performance of the HSES by predicting the pre-arcing time within the short-circuit current making test. To estimate the pre-arcing time, we compared the results of analytical calculations based on streamer discharge theory and the numerical simulations of the electric field strength. By conducting a short-circuit current making test for a 420 kV 63 kA HSES in a high-power laboratory, the pre-arcing time calculation results were verified. A comparison of the results showed that the proposed prediction method was useful for verifying the performance of the HSES. [ABSTRACT FROM AUTHOR]

This paper investigates the feasibility of a cost effective method to prevent internal resonance in power transformers connected to gas insulated substation (GIS) due to very fast transient overvoltage (VFTO) within the GIS. Power transformer internal resonance takes place if one of the VFTO frequencies matches with the transformer natural frequency. If the system is not equipped with adequate damping scheme for such transients, transformer catastrophic failure may take place causing harmful impacts on the environment including fire and oil spillage. In this paper, the feasibility of utilizing RC surge suppressor to avoid power transformer internal resonance is investigated through the simulation of a real 400kV gas insulated substation located in the north of Iran and connected to a 250MVA, three phase power transformer. Several RC design topologies are analysed and the most effective topology to suppress high risk frequencies of VFTO is highlighted. In contrary to the existing resonance suppressing approaches that call for modifications in the GIS infrastructure, the proposed method in this paper is a cost effective technique that can be implemented within existing gas insulated substations without any change in its structure. [ABSTRACT FROM PUBLISHER]

Overcurrent relays are the most economical protective relays that are used as main/backup protection in distribution networks and as backup protection in transmission and subtransmission networks. The most effective overcurrent relays have inverse time-current characteristics such as standard (normal) inverse (SI) characteristic, very inverse (VI) characteristic, and extremely inverse (EI) characteristic. Lately, the use of numerical protective relays is considered due to their programmable functionality, greater flexibility, higher speed, and accuracy. Numerical overcurrent relays usually allow the users to define and setup arbitrary time-current characteristics. This paper aims to develop a new time-current characteristic to be used in numerical overcurrent relays to overcome some drawbacks of the conventional characteristics. This characteristic curve is constructed by connecting successive straight lines and can easily be tabulated to write to the numerical relays. [ABSTRACT FROM AUTHOR]

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

Although a wide variety of different types of electrically protective devices is used nowadays, industrial facilities witness constant growth in the number of failures of power station and substation switchgear components due to various reasons. Many specialists working in the power-engineering sphere express opinions that the facilities should be equipped with protection that operates in case of busbar faults. The given article investigates peculiarities in the design of the busbar differential current protection instrument that employs Rogowski coils as primary current transducers. A design of a noise-immune sectionalized Rogowski coil with double-layer winding is suggested, which makes it possible to significantly improve operational performance of busbar differential protection. Main attention is paid to methods of mathematical modeling of transient processes in busbar differential protection, based on designs of such coils developed in the Far Eastern Federal University. The article dwells upon theoretical research and technical features to be taken into account while developing modeling schemes of longitudinal differential protection of a three-phase busbar system based on Rogowski coils. Results of protection modeling in Micro-Cap software are described. Based on the analysis of data acquired during modeling; a valid conclusion is made about advantages of using Rogowski coils in busbar differential protection, which provides improvement of sensitivity and speed of response of such protective devices. [ABSTRACT FROM AUTHOR]

Power system blackouts are very infrequent, but they have a Brobdingnagian effect on the system performance and devices. The present research work offers remarkable techniques for the assessment of temporary overvoltages all through the re-energization of network lines. The main goal of this research work is to first-rate and reenergize the network lines for the purpose of restoration. In the later stage, the magnitudes and durations of the Temporary Overvoltages (TOVs) that occurred during the energization of unloaded transformer are estimated. The assortment and re-energization of network lines is done on the basis of Data Envelopment Analysis (DEA) and conceptual method respectively. The assessment of TOVs is done on the basis of MATLAB/Simulink and Feed Forward Neural Networks (FFNNs). The proposed models are verified on IEEE 30 bus test system for the analysis purpose. The Mean Absolute Percentage Error (%MAPE) obtained through various forecasting methods is examined to check the robustness of the proposed approaches. The simulation and FFNN results presented in this research work helps in designing the exact withstand voltage rating for various network components employed at the moment of re-energization. [ABSTRACT FROM AUTHOR]

Transient overvoltages due to circuit-breaker switching may occur if certain conditions regarding system layout and type of switching operations are fulfilled. In such applications, overvoltage protection should be used. Different types of protective devices exist, such as surge arresters and RC snubbers, and they can be installed in different configurations. The purpose of the presently published results is to show the effect of the different protective devices. Laboratory testing has been performed, focusing on the disconnection of an inductively loaded transformer at a phase angle causing multiple reignitions. It was found that surge arresters limit the voltages to well-defined amplitudes, but a number of reignitions occur up to this level. RC snubbers, on the other hand, reduce the risk of having reignitions and the number of reignitions in case they do occur, but the voltages are not limited at well-defined amplitudes. All of the tested configurations of protective devices limited the voltages below the basic insulation level of the transformer. [ABSTRACT FROM PUBLISHER]

High-impedance fault location has always been a challenge for protection engineering. On the other hand, if this task is successfully realized, maintenance action could be performed in order to avoid potential injuries. For an effective protection scheme, high-impedance fault location should be performed, but a lack of research on this area is noted. This paper proposes a new analytical formulation for high-impedance fault location in power systems. The approach is developed in the time domain, considering a high-impedance fault model consisting of two antiparallel diodes. Using this model, the fault distance and parameters are estimated as a minimization problem. First, a linear least square-based estimator is applied without consideration of line capacitance. Second, a steepest descent-based estimator is proposed in order to consider the line capacitance. Studies were carried out with the IEEE 13 bus modeled in the Alternate Transients Program. Encouraging test results are found indicating the method's potential for real-life applications. [ABSTRACT FROM PUBLISHER]

In this paper, an overview of the main motor features influencing the protection devices settings is presented, pointing out key differences between three-phase direct-on-line (DOL) motors of different efficiency classes. The results of experimental tests and simulations are presented and discussed in the scope of the motor protection against overload, short-circuit, current unbalance, and locked-rotor conditions, for 7.5-kW, four-pole, IE2- and IE3-class squirrel-cage induction motors (SCIMs) and for IE4-class line-start permanent-magnet motors (LSPMs), offering important data related to their electrical and thermal behaviors. Two commercial digital thermal-magnetic motor protection devices, whose thermal models were designed for IE1- and IE2-class motors, are evaluated in terms of operation effectiveness in the tested motors. This paper is important for industry due to the significant penetration of IE3-class induction motors, as well as to the recent introduction into the market of IE4-class induction motors and LSPMs. [ABSTRACT FROM PUBLISHER]

DC microgrid systems with hybrid energy resources are of significant interest in shipboard and spacecraft applications. In such a system, coordinated operation of circuit breakers (CBs) and disconnecting switches (DSs) can rapidly isolate short-circuit faults and restore the system very fast. In this paper, we investigate a new protection scheme for a Multi-Bus dc systems based on an event classification approach. The proposed protection scheme transfers less data when compared with commonly used data-based protection methods and does not require high-speed communication and synchronization. The results show that the developed protection scheme is able to identify the type of fault accurately, isolate the faulted area, and restore the system very quickly while maintaining continuous power to the loads. [ABSTRACT FROM PUBLISHER]

This paper presents the development of a short-circuit protection mechanism on a high voltage switch (HVS) board which is built by a series connection of semiconductor switches. The HVS board is able to quickly detect and limit the peak fault current before the signal board triggers off a gate signal. Voltage clamping techniques are used to safely turn off the short-circuit current and to prevent overvoltage of the series-connected switches. The selection method of the main devices and the development of the HVS board are described in detail. Experimental results have demonstrated that the HVS board is capable of withstanding a short-circuit current at a rated voltage of lOkV without a di/dt slowing down inductor. The corresponding short-circuit current is restricted to 125 A within 100 ns and can safely turn off within 120 ns. [ABSTRACT FROM AUTHOR]

The electromagnetic shielding behavior of fabrics woven with carbon/stainless steel/polypropylene (C/SS/PP) hybrid yarns were investigated in the frequency range of 300 kHz to 1.5 GHz. This study mainly emphasizes the electromagnetic shielding behavior of C/SS/PP hybrid yarn fabric and the effect of different fabric parameters such as pick density, fabric architecture and number of fabric layers on shielding effectiveness (SE) of fabrics with C/SS/PP hybrid yarns. The SE of fabric samples were tested by a vector network analyzer using a coaxial transmission line tester. In addition, surface images of different fabric structures were examined to appreciate the effect of yarn floats on the shielding behavior of fabrics. From the SE test, it was observed that an increase in pick density increases the SE of C/SS/PP hybrid yarn fabric due to addition of carbon and SS content in the fabric. Besides, the fabric cover and pore area distribution are also changed for varying pick densities. Essentially, a fabric's architecture plays an important role in the fabric cover and pore area distribution. The one-end float (1/1 plain) fabric of 6.3 ppcm provides higher shielding of 88.44 dB than a 4-end (4/1 twill) or 7-end float (8-end satin) fabrics of 6.3 ppcm. Moreover, an increase in the number of fabric layers also improves the SE of fabrics. The developed C/SS/PP hybrid yarn fabric can be used for shielding wireless transmissions, radar transmissions and for shielding panels. [ABSTRACT FROM AUTHOR]

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

A novel sort of cellular titanium foam with the porosity of 86–90% and the main-pore size of 0.5–3.0 mm was successfully prepared. Such foam exhibited a compressive curve showing three regimes: the initial elasticity, the middle zigzag plateau, and the final “densification.” This “densification” presented a course that the broken pieces continually accumulated in those pores which were unbroken or not entirely broken. The fracture morphology suggested that the compressive failure was typically brittle for this titanium foam. The electromagnetic shielding performance was investigated in the radio wave frequency range (0.3–3000 MHz) for this foam, which showed an evident effectiveness with a good performance at low frequencies. On the whole, the effectiveness would be superior while the porosity of the sample was relatively small. It could be inferred that the present foam samples would perform their electromagnetic shielding mainly by the reflection loss mechanism in the low-frequency range, and give priority to the absorption loss mechanism at the upper-frequencies. [ABSTRACT FROM PUBLISHER]

In this paper the short-circuit current of overhead transmission lines is analyzed at a short circuit in an HVDC transmission network. The analysis focuses solely on the current contribution of the transmission line at a line-to-earth or a line-to-line short circuit. In this context it is shown which impedance is effective at the corresponding fault case. Special attention is given to the frequency dependence of the line parameters and how they affect the short-circuit current. The frequency of the current is derived with a simplified method. Finally, it is presented how the resulting time course of the short-circuit current can be determined based on travelling wave theory. The analysis covers different HVDC grid topologies. [ABSTRACT FROM AUTHOR]

This paper presents a new methodology to obtain the line impedance of current railway tracks by using only short-circuit measurements. Open-circuit measurements required by conventional methodologies are discarded, since they cannot be carried out for railway tracks in service (electrically continuous and indefinite length). The mathematical basis of the proposed methodology is based on the transmission line theory but focused on the changes in track length. The proposal has been successfully applied to characterize the impedance of the high-speed railway line at the Spanish AVE Madrid-Valencia (Cuenca) and in the AVE Atocha-Chamartin tunnel (Madrid). Copyright © 2014 John Wiley & Sons, Ltd. [ABSTRACT FROM AUTHOR]

Surge protective device is widely used in the lightning protection of electric appliances. In order to meet the withstand voltage level of those protected devices, multi-level surge protective devices are applied in the practical situation. Therefore, the optimal choice of decoupling elements is vital to realize the energy coordination between multi-level surge protective devices. This paper intends to expatiate on the process of coordination between these low-voltage multi-level surge protective devices, which is based on the transmission line theory. Through a series of experiments, we found the transmission line theory could be applied to describe the transmission process of lightning wave in the low-voltage system; When a 5-meter-long wire whose inductance is 5.6 micro-henry was used as the decoupling element, the average shunt ratio between multi-level surge protective device in the first level and multi-level surge protective devices in second was about 0.9: 0.1; upon the experimental results, it was proposed that two voltage limiting type multi-level surge protective devices had a better performance to clamp the overvoltage, which has a certain reference value in the practical application. [ABSTRACT FROM AUTHOR]

In order to study electrical properties, especially the electromagnetic interference (EMI) shielding property of ternary Ni-P-Cu plated polyether ether ketone/carbon fiber composites (CFs/PEEK) and their dependence on Cu content of the coating, electroless Ni-P coating was first deposited on CFs/PEEK to obtain the optimum conditions for deposition rate, then a small quantity of CuSO4•5H2O (0.1∼0.4 g/L) was added in the electroless nickel-based alloy plating (ENP) bath to investigate the influence of Cu content on the deposition rate and coating characterizations. The EMI shielding effectiveness (SE) was evaluated and corrosion resistance was characterized by electrochemical polarization measurement. It was found that coating phase change from amorphous to a mixture of amorphous and microcrystalline phases with the increase of Cu2+ concentration. Due to the neat morphology and uniform amorphous structure, the optimum coating Ni-P-2.2 wt% Cu obtained at the 0.2 g/L Cu2+ in the bath owns the best corrosion resistance, EMI SE and the lowest surface resistance. POLYM. COMPOS., 36:923-930, 2015. © 2014 Society of Plastics Engineers [ABSTRACT FROM AUTHOR]

Purpose. Theoretical justification and engineering of induction motors heat protection method from overload currents taking into account nonlinear distortion of the phase current and implementation as a microprocessor device functioning algorithm. Methodology. To solve the problem used the theory of the representing complex harmonic oscillations analog signals expansion into the oscillation spectrum forming elementary harmonic components in order to compare their properties by applying the theory of discrete signals and systems, as well as methods of spectral analysis and discrete signals filtering. The harmonic analysis versatility is that any periodic signal may be synthesized from harmonic oscillation of certain amplitude, frequency and initial phase. A mathematical model for determining the phase current harmonic content of power supply networks with isolated neutral and non-linear loads types and, as a consequence, the distortion of sinusoidal phase current change is developed by multiplying the analog current in time dependency on the grate delta-function with different sampling intervals, in which the use of simple and widely used in relay protection units, in particular electronic overcurrent relays, mathematical operations of integration squares instantaneous current allows the most in harmony with the mathematical tools to build other network protection types. Findings. The necessity to increase the sensitivity of the induction motors heat protection from overload currents taking into account nonlinear distortion of the phase currents is proved. By nonlinear distortion harmonic analysis of the phase currents the motor protection reliability increasing provided by taking into account the higher harmonic components of the phase currents, which causes to additional losses and heating of the stator winding. It uses the simplest and widely used in protective relaying mathematical apparatus determining of most significant higher harmonics currents RMS. Originality. A possibility of extending the implemented protection list of electronic overcurrent relays based on the digital processing of signals from the current sensors is theoretical research by the harmonious analysis of phase current spectrum with the nonlinear distortions presence. A new technical solution is proposed that allows in online sliding monitoring mode to form response time of electronic overcurrent relays for reliable protection of induction motors from overload currents taking into account nonlinear distortion of the phase current. Practical value. A microprocessor protection functioning algorithm of induction motors is designed against impermissible heating coils with overload currents taking into account nonlinear distortion of the phase current. [ABSTRACT FROM AUTHOR]

To validate the performance of a small-volume neon-filled tube in overvoltage protection, the characterization of the neon-filled tube at p = 6.6 mbar and with 1-cm ^{3} volume was performed. The characterization was performed using the mean value of electrical breakdown time delay \overline t_{d} data as a function of relaxation period \tau , applied voltage U_{w} , and discharge current I_{g} . On the basis of \overline td data as a function of \tau , it was shown that after discharge, the gas full recovery appears for \tau \approx 7~\textrm ms . The increase in the applied voltage in the case of full gas recovery leads to the decrease in \overline td and for Uw \ge 130~\textrm {V} , \overline td \approx \textrm {constant.} This proves the tubes efficient usage in overvoltage protection for applied voltages higher than 130 V. The increase in discharge current leads to the decrease in \overline td in a considered \tau interval. Other important processes that occur in discharge and afterglow, which are responsible for the initiation of electrical breakdown in neon-filled tube, were also analyzed. [ABSTRACT FROM PUBLISHER]

A laterally-driven inertial micro-switch was designed and fabricated using surface micromachining technology. The dynamic response process was simulated by ANSYS software, which revealed the vibration process of movable electrode when the proof mass is shocked by acceleration in sensitive direction. The test results of fabricated inertial micro-switches with and without anti-shock beams indicated that the contact process of micro-switch with anti-shock beams is more reliable than the one without anti-shock beams. The test results indicated that three contact signals had been observed in the contact process of the inertial switch without anti-shock beams, and only one contact signal in the inertial switch with anti-shock beams, which demonstrated that the anti-shock beams can effectively constrain the vibration in non-sensitive direction. [ABSTRACT FROM AUTHOR]

Microgrids work in two modes, grid connected and islanded. Short circuit levels in islanded mode tend to be small compared to those in grid-connected mode. Moreover, power flows in microgrids are not always unidirectional. For these reasons, it is difficult to protect microgrids using relaying strategies traditionally used in distribution systems. In this paper, a new technique is presented which uses a state observer to detect and identify faults that occur within the zone of protection, regardless of whether the microgrid is islanded or grid connected. The proposed system can be centralized or decentralized. In addition, based on system observability, the required number of measurements can be reduced, thereby reducing the cost of the proposed protection system. It is possible to devise a low-cost protection system using the proposed approach. The performance of the proposed method in protecting IEEE 34 node test feeder is demonstrated on an Alternative Transient Program (ATP). The proposed approach is shown to be effective in grid-connected and islanded modes. Copyright © 2014 John Wiley & Sons, Ltd. [ABSTRACT FROM AUTHOR]