Sudden Voltage Changes Research Articles

Study on Effect of Activation Procedure on Anion Exchange Membrane Water Electrolyzer Using Ni-Mo Electrocatalyst for Hydrogen Evolution Reaction

Hydrogen Evolution Reaction (HER) in Anion Exchange Membrane Water Electrolyzer(AEMWE) requires fewer electrons compared to the oxygen evolution reaction, which is why research on it started later. However, when using an anion exchange membrane, the hydrogen evolution reaction occurs in multiple steps, and the dissociation of water is requisite first. The water splitting is challenging, hence catalysts that enhance water decomposition are essential. Currently, Platinum supported by carbon is used as the most stable and efficient material for HER. However, due to Platinum is rare and expensive, leading to significant research into alternative materials. Among various non-precious metal candidates, Nickel is known for its superior hydrogen evolution performance. Yet, the performance of Nickel alone is inferior to that of Platinum. Nickel exhibits enhanced performance and durability when combined with other metals due to a synergistic effect. The second metal, such as Copper, Cobalt, Iron, or Molybdenum, shows improved performance when alloyed with Nickel . Amon them Ni–Mo catalyst has shown high activity for HER in AEMWE. Among various Ni/Mo molar ratios, the catalyst showed the highest activity when it was 3. With Ni3Mo as the cathode, a single cell was fabricated using non-noble metal catalysts exclusively. Interestingly, the activation procedure significantly affected the cell performance. The single cell performed better than that with the Pt/C catalyst when the Ni3Mo catalyst was activated at 50 mA/cm2. Molybdenum tends to dissolve once the reaction begins the distribution of Mo in electrodes, membrane, and electrolytes was estimated, confirming Mo dissolution from the cathode. Once the cell was activated, the cell performance was stable without degradation in long-term chronopotentiometry operation, but the performance was degraded by sudden voltage change such as imposing open circuit voltage . The surface structure and reaction mechanism were studied with density functional theory: the Mo-dissolved Ni3Mo(101) surface could promote H2O dissociation, while MoO3 stably adsorbed on the surface weakened H* adsorption, promoting HER. This study provides important insights into the development of efficient catalysts for large-scale hydrogen production.

Ground Electric Field, Atmospheric Weather and Electric Grid Variations in Northeast Greece Influenced by the March 2012 Solar Activity and the Moderate to Intense Geomagnetic Storms

In a recent paper, we extended a previous study on the solar solar influence to the generation of the March 2012 heatwave in the northeastern USA. In the present study we check the possible relationship of solar activity with the early March 2012 bad weather in northeast Thrace, Greece. To this end, we examined data from various remote sensing instrumentation monitoring the Sun (SDO satellite), Interplanetary space (ACE satellite), the Earth’s magnetosphere (Earth-based measurements, NOAA-19 satellite), the top of the clouds (Terra and Aqua satellites), and the near ground atmosphere. Our comparative data analysis suggests that: (i) the winter-like weather (rainfall, fast winds, decreased temperature) in Thrace started on 6 March 2012, the same day as the heatwave started in USA, (ii) during the March 2012 winter-like event in Thrace (6–15 March), the ACE satellite recorded enhanced fluxes of solar energetic particles (SEPs), while SOHO and PAMELA recorded solar protons at very high energies (>500 MeV), (iii) Between 3–31 March, the temperature in Alexandoupoli and the ACE/EPAM solar high energy (1.88–4.70 MeV) proton flux were strongly anticorelated (r = −0.75, p = 0.5). (iv) Thrace experienced particularly intense cyclonic circulation, during periods of magnetic storms on 8–10 and 12–13 March, which occurred after the arrival at ACE of two interplanetary shock waves, on March 8 and March 11, respectively, (v) at the beginning of the two above mentioned periods large atmospheric electric fields were recorded, with values ranging between ~−2000 V/m and ~1800 V/m on 8 March, (vi) the winter-like weather on 8–10 March 2012 occurred after the detection of the main SEP event related with a coronal mass ejection released in interplanetary space as a result of intense solar flare activity observed by SDO on 7 March 2012, (vi) the 8–10 March weather was related with a deep drop of ~63 °C in the cloud top temperature measured by MODIS/Terra, which favors strong precipitation. Finally, we analyzed data from the electric power network in Thrace (~41°N) and we found, for the first time sudden voltage changes of ~3.5 kV in the electric grid in Greece, during the decay phase of the March 2012 storm series. We discuss the winter-like March 2012 event in Thrace regarding the influence of solar cosmic rays on the low troposphere mediated by positive North Atlantic Oscillation (NAO). Finally, we infer that the novel finding of the geomagnetic effects on the electric power grid in Thrace may open a new window into space weather applications research.

Analysis of an accident of abnormal increase in pole bus differential current caused by DC line faults

This paper analyzes an accident of abnormal increase of pole bus differential current and pole differential current of a converter station caused by line fault of a ±800 kV extra high-voltage direct current transmission project. After a lightning strike caused a short circuit and grounding of the DC line, the sudden voltage change protection of the DC line was triggered and the DC full voltage restart was successful. The pole bus differential current and pole differential current of the converter station have reached the protection set but have not reached the protection delay set; therefore, the differential protection has not acted. This paper first introduces the configuration principles of pole differential protection, pole bus differential protection, and line voltage sudden change protection for extra-high voltage converter stations. Second, the operation of the DC protection under this fault was analyzed in detail, and the reasons for the occurrence of pole bus differential current and pole differential current were also analyzed in this paper. Then, the range of equipment that caused the abnormal increase in differential current was identified. Finally, the lightning strike model was built on the real-time digital system, and the fault was simulated and replicated. It was determined that the abnormal increase in differential current was caused by the discharge of the pole bus surge arrester caused by the second lightning strike on the DC line.

Impact of Virtual Inertia on DC Grid Stability With Constant Power Loads

Virtual inertia is an effective control approach to attenuate sudden voltage changes during transient events in low-inertia DC grids. While methods have been proposed to implement virtual inertia, its impact on DC grid stability in the presence of constant power loads (CPLs) remains unclear. In this paper, we perform a rigorous stability analysis for DC grids with CPLs powered by virtual-inertia-enhanced converters. We derive a closed-form stability criterion that can be used to evaluate the impact of virtual inertia on the system stability, and demonstrate that, given a set of system parameters, the stability of a DC grid powering CPLs can be improved for a range of virtual inertia designs. We provide analytical expressions for the optimal virtual inertia that improves stability and for the maximum virtual inertia that does not deteriorate stability. In addition, we present a step-by-step guideline to design a stable DC grid with virtual inertia. Test results are presented to validate the analysis.

An adaptive time–frequency approach based secured back-up distance protection scheme for system stress conditions

Critical operating conditions of power system may lead to distance relay security issues. Distance relay back-up protection is offered with long reach setting and due to this under sudden change in voltage and current parameters during non-fault situations also considered as a fault by the protection function in an integrated network. The conventional technique fails to discriminate system stress conditions such as power swing, voltage instability and load encroachment from an actual symmetrical fault in the back-up zone (third zone (Z3)) of the distance relay. To mitigate this, a Modified Complete Ensemble Empirical Mode Decomposition with Adaptive Noise (MCEEMDAN) technique is used to decompose the instantaneous power and to develop a reliable index. The most significant intrinsic mode function (IMFs) is extracted to estimate the energy as used as detection index. An adaptive statistical threshold selection process is developed to detect and discriminate all system stress conditions from symmetrical fault in the back-up zone of the distance relay. The proposed algorithm is a supervisory scheme for the back-up zone setting (Z3) of the distance relay. Simulation results for different stress conditions, presence of noise, sudden switching of load and symmetrical fault are presented to highlight the strength of the method.

Radio-Absorbing Materials Based on Polymer Composites and Their Application to Solving the Problems of Electromagnetic Compatibility.

Recently, designers of electronic equipment have paid special attention to the issue of electromagnetic compatibility (EMC) of devices with their own components and assemblies. This is due to the high sensitivity of semiconductor microcircuits to electromagnetic interference. This interference can be caused either by natural phenomena, such as lightning strikes, or by technical processes, such as transients in circuits during fast periodic or random switching. Either way, interference implies a sudden change in voltage or current in a circuit, which is undesirable, whether it propagates along a cable or is transmitted as an electromagnetic wave. The purpose of this article is to review the works devoted to the development, creation, and investigation of modern polymeric nanocomposite materials used for shielding electromagnetic radiation and their effective application for solving problems of electromagnetic compatibility. Additionally, the approach to design EMI shielding complex media with predetermined parameters based on investigation of various properties of possible components is shown. In the review, all polymer composites are classified according to the type of filler. The issues of the interaction of a polymer with conductive fillers, the influence of the concentration of fillers and their location inside the matrix, and the structure of the nanocomposite on the mechanisms of electromagnetic interaction are considered. Particular attention is paid to a new generation of nanocomposite materials with widely adjustable electrical and magnetic properties. A wide class of modern filled polymeric materials with dielectric and magneto-dielectric losses is considered. These materials make it possible to create effective absorbers of electromagnetic waves that provide a low level of reflection coefficient in the microwave range. The model mechanisms for shielding electromagnetic radiation are considered in the paper. A detailed review of the electro-physical properties of polymer nanocomposites is provided. Multilayer electrodynamic media containing combinations of layers of filled polymer composite materials with nanoparticles of different compositions and manufactured using a single technology will make it possible to create electrodynamic media and coatings with the required electro-physical characteristics of absorption, transmission, and reflection. Within the framework of the two-layer coating model, the difference in the effects of the interaction of electromagnetic radiation with conductive layers located on a dielectric and metal substrate is demonstrated. It is shown that in order to achieve optimal (maximum) values of reflection and absorption of electromagnetic radiation in the appropriate frequency range, it is necessary to fit the appropriate layer thicknesses, specific conductivity, and permittivity. Such approach allows designers to create new shielding materials that can effectively vary the shielding, absorbing, and matching characteristics of coatings over a wide frequency band. In general, it can be said that the development of innovative polymer composite materials for shielding electronic devices from electromagnetic interference and excessive electromagnetic background is still an important task. Its solution will ensure the safe and uninterrupted operation of modern digital electronics and can be used for other applications.

Static Analysis and Optimization of Voltage and Reactive Power Regulation Systems in the HV/MV Substation with Electronic Transformer Tap-Changers

The quality of electricity is a very important indicator. The durability and reliable operation of all connected devices depend on the quality of the network voltage. Rapid changes in loads, changes in network connections and the presence of uncontrolled energy sources require the development of new voltage regulation systems. This requires voltage regulation systems capable of responding quickly to sudden voltage changes. In substations with control transformers, it is possible thanks to the use of semiconductor tap changers. Moreover, voltage regulation and reactive power compensation systems should be built as one system. This is due to the close dependence of voltage and reactive power in the network node. Therefore, it was proposed to use artificial intelligence methods to build a new voltage regulation and reactive power compensation system using all measurement voltages of network nodes. In the first stage of the research, active and reactive powers, as well as the voltage of the reference node, were selected for 6420 periods of the mains voltage. The simulation results were compared for the classic voltage regulation system with semiconductor tap changers and the evolution algorithm based on voltage measurements from the entire MV network. A significant improvement in the quality of voltage regulation with the use of an evolutionary algorithm was demonstrated. Then, a second set of input data with increased values of reactive power was generated. The results of the evolutionary algorithm after the application of the classic, independent reactive power compensation system and two-criteria optimization were compared. It has been shown that only the two-criteria optimization algorithm keeps both |tgφ| within the acceptable range and the quality of voltage regulation is the best. The article compares different working algorithms for semiconductor tap changers.

Outgassing during large area field emitter operation in the diode system

We report peculiar emission behavior of large-area cathode based on a multiwalled carbon nanotube/polymer nanocomposite. Mass spectra and kinetics of the partial pressure of the main volatile products released from the surface of the electrodes were obtained when a constant voltage of different levels was applied to the cathode. The main volatile products during field emission diode operation are H2, H2O, CO/C2H4, and CO2. The behavior of H2O peak intensity is characterized by increased inertia relative to sudden voltage changes.

Dynamic characteristics of proton exchange membrane fuel cell on a multiple time scale

The current research on the dynamic performance of the proton exchange fuel cell is mostly aimed at the influence of operating parameters on the system, but does not involve with the dynamic characteristics of the cell on a multiple time scale nor the study of the corresponding multiple time scale model. In order to detect the dynamic changes of the proton exchange membrane fuel cell, the effects of various factors in the system on the output performance on different time scales are investigated. The effective partial pressure of oxygen and hydrogen are obtained by the mass diffusion equation and the ideal gas state equation, and the dynamic model is established according to the law of conservation of energy, the law of thermodynamics, and the electrochemical reaction equation. By setting the load mutations with a large/medium/small time scale dynamic duration of 0.6 s, 165 s, and16 min, respectively, the mechanism with which voltage suddenly changes when the load current changes abruptly is studied. Starting from the long time constant during which the dynamic performance takes effect, the control variable is used to analyze the double-layer charge. The influences of layer effect capacitance <i>C</i>, fuel oxidant delay time constant <i>τ</i><sub>e</sub>, and thermodynamic characteristics (temperature <i>T</i>) on the dynamic performance ( initial values of variables: <i>C</i> = 4 F, <i>τ</i><sub>e</sub> = 80 s, and <i>T</i> = 307.7 K) clarify the action intensities on different time scales. With the help of Matlab/Sumlink platform the simulation results are obtained and the correctness and effectiveness of the built model are verified. The simulation results show that the sudden change in voltage is due to the open circuit voltage and Ohmic polarization resistance, and the Ohmic resistance is dominant (the Ohmic overvoltage change value is 2 V, and the open circuit voltage change is 0.05 V), and the <i>C</i> pair dynamics on a small time scale (ms). The performance plays a leading role. Specifically, <i>τ</i><sub>e</sub> has a greater effect on the dynamic characteristics on a medium time scale (s), and <i>T</i> has a stronger effect on a large time scale (10<sup>2</sup>–10<sup>3</sup> s). Based on the above deduction, a multi-time scale model of the battery is derived. The research provides the reference and theoretical support for subsequent battery energy management, evaluation of dynamic performance, and precise control.

Single-Ended Fast Protection for Transient Power of Multi-Terminal Flexible and Direct Power Grids Containing Renewable Energy

With the proposal of the carbon peak goal, a multi-terminal flexible DC grid containing various renewable energy becomes the one of main ways of renewable energy power transmission. Thus, it is increasingly important to improve its transmission reliability and stability. This paper proposes a single-ended protection principle based on the analysis method of transient power change for the “mesh structure” ring-shaped flexible direct current (DC) grid. Based on the propagation characteristics of voltage, current, and anti-traveling waves during fault periods, the transient power variation coefficient based on SOD transformation is introduced to distinguish the internal and external faults. Besides, simulation based on the PSCAD/EMTDC platform within the Zhangbei four-port network verifies the effectiveness of the proposed protection principle under various fault conditions. Meanwhile, the protection criterion is designed according to the difference in the change coefficient of the transient power SOD within and outside the fault time zone. Moreover, the setting value of the start of protection is obtained by analyzing the simulation results, thus a set of fast and reliable single-ended protections for the same-side short-time transient power window of an enhanced flexible straight power grid is developed via combining it with the starting criterion of a sudden voltage change.

Non-Dissipative Snubber Circuit Based SEPIC Converter for High Static Gain Applications

In this paper different non-dissipative snubber circuits in which RCD snubber circuit, CD snubber circuit, LCD snubber circuit and proposed LCD snubber circuit are implemented in SEPIC converter to obtain high static gain. The snubber circuit is used for the protection of the power semiconductor devices. The requirement of high static gain is necessary in different applications of dc-dc converters, so that efficient operation of the system can be obtained. The basic idea of the snubber circuit used in this paper is to reduce the turn-on and turn-off losses at the time of switching processes. For this purpose, inductor and capacitor combination is required so that during turn-on process, sudden change in current through semiconductor device which is used as a switch, can be reduced. Similarly, during turn-off process, sudden change in voltage across switch can be minimized. Here, different snubber circuit based SEPIC converters are analyzed with the help of MATLAB simulink and results of output voltages and currents are obtained. The results are summarized which clearly shows that the proposed SEPIC converter has high static gain in comparison of the others topologies. Hence non-dissipative snubber circuit based SEPIC converter provides high efficiency than the other modifications in SEPIC converter.

Modelling a Disconnect Switch

Abstract This article presents a model to simulate disconnecting switches in transient studies. The distance between contacts of a disconnecting switch does not change instantaneously; it takes several seconds to complete the full movement from closed to open, or vice-versa. The disconnecting switches are able to operate with lower current amplitudes, so a disconnecting switch is operated only when the circuit breaker is in open position. However, even with the circuit breaker open, there is a current flowing through the grading capacitors. The grading capacitors in conjunction with the busbar capacitance form a capacitive divider, and there is a floating voltage in the busbar. When the contacts of the disconnecting switch move, the withstand voltage varies and an electric arc appears. This arc is unstable and is interrupted and reignited several times. Each arc reignition causes a sudden voltage change that propagates through the busbar and impacts any connected equipment. The developed model, with the withstand voltage variation and the electric arc behaviour taken into account, calculates the fast transient overvoltages originated during a disconnecting switch operation. The amplitude and waveform of these overvoltages may then be used to evaluate the impact on insulation ageing.

Decentralized Synergetic Power System Stabilizer

This paper presents a decentralized synergetic power system stabilizer (DSPSS). The nonlinear control law was synthesized by introduction of invariant manifolds into the state space of studied system, synchronous machine connected to infinite bus. The invariant manifold was defined as a linear combination of the generator terminal voltage, rotor speed and active power deviation to achieve coordination of the synchronous generator electromechanical oscillation damping and terminal voltage control. Compared to other synergetic power system stabilizers, this one uses real time Park’s transformation to calculate dq-components of generator currents and voltages. Also, a novel approach for calculation of a generator voltage derivative is presented, and the proposed stabilizer is less sensitive to sudden voltage changes and measurement noise. DSPSS control law was implemented on real-time hardware platform and experimentally tested on an 83kVA synchronous hydrogenerator. Experimental results for the power and voltage reference step change, loss of the transmission line and three phase short circuit were conducted using DSPSS and PSS2A stabilizers. Furthermore, the results showed that the proposed DSPSS stabilizer was robust to system parameter changes and has better dynamic response than the classic PSS2A in case of small and large disturbances.

Assessment of Sudden Voltage Changes and Flickering for a Grid-Connected Photovoltaic Plant

In this paper, sudden voltage changes studies are carried out for a 20 MW grid-connected photovoltaic plant to assess the impact of energization of the step-up transformers, which may cause a voltage dip that could be a nuisance to the point of common coupling (PCC) of the transmission system. In addition, the flicking performance of the plant is checked. At the design stage, these studies are necessary to verify compliance of the photovoltaic plant and to design its connection with regulatory grid codes and international standards. The photovoltaic plant is compliant with the FICHTNER standard for long-term flicker severity and with the short-term flicker severity requirements of Engineering Standard P28. Based on the study results, the main breaker which is connected to the PCC should be ordered with 150 Ohm Pre-Insertion Resistor to make the Photovoltaic plant comply with grid code requirements of sudden voltage changes.

A time-domain statistical approach for harmonics separation and analysis

Summary The paper proposes a novel time-domain statistical method to separate and analyze harmonics based on single channel analysis and principal component analysis. The proposed method separates the fundamental wave and harmonics to provide specific time-domain information. Two identification methods are proposed to estimate the number of harmonics within the power system signal, even with high noise. This paper validates the effectiveness of the proposed method through mathematical deduction and studies the selection of Euclidean embedding dimension. The robustness of the proposed method is tested on several simulated synthetic signals and a real-world signal. Simulation results show that the proposed method can detect harmonics with small amplitude in the presence of noise and has better separated waveform and less execution time than wavelet-packet transform and empirical mode decomposition. It is also shown that the proposed method can detect sudden voltage changes and separate disturbances.

A Transformer Inrush Reduction Technique for Low-Voltage Ride-Through Operation of Renewable Converters

The low-voltage ride-through (LVRT) capability is a critical requirement of grid-connected converters of renewable energy resources to uphold the stability of the power system. The step-up transformer that connects the power converter to the grid is exposed to sudden voltage changes throughout the LVRT, and the resulting magnetic flux deviation often leads to severe inrush current when the grid fault clears. The inrush current exerts significant mechanical forces in the transformer and damages its insulation. This paper proposes a control method of the power converter to reduce the risk of inrush current by mitigating the magnetic flux deviation during the LVRT operation. The proposed method also manages the output current of the power converter within the capacity of semiconductor devices to reduce their stress while performing the proposed flux compensation and other LVRT operations. The reliability of the power converter and the transformer can be improved by the proposed control method.

Assessment of Sudden Voltage Changes and Flickering for a Grid-Connected Photovoltaic Plant

Assessment of Sudden Voltage Changes and Flickering for a Grid-Connected Photovoltaic Plant

Competitive behavior of photons contributing to junction voltage jump in narrow band-gap semiconductor multi-quantum-well laser diodes at lasing threshold

The junction behavior of different narrow band-gap multi-quantum-well (MQW) laser diodes (LDs) confirmed that the jump in the junction voltage in the threshold region is a general characteristic of narrow band-gap LDs. The relative change in the 1310 nm LD is the most obvious. To analyze this sudden voltage change, the threshold region is divided into three stages by Ithl and Ithu, as shown in Fig. 2; Ithl is the conventional threshold, and as long as the current is higher than this threshold, lasing exists and the IdV/dI-I plot drops suddenly; Ithu is the steady lasing point, at which the separation of the quasi-Fermi levels of electron and holes across the active region (Vj) is suddenly pinned. Based on the evolutionary model of dissipative structure theory, the rate equations of the photons in a single-mode LD were deduced in detail at Ithl and Ithu. The results proved that the observed behavior of stimulated emission suddenly substituting for spontaneous emission, in a manner similar to biological evolution, must lead to a sudden increase in the injection carriers in the threshold region, which then causes the sudden increase in the junction voltage in this region.

Fault-induced delayed voltage recovery in a long inhomogeneous power-distribution feeder.

We analyze the dynamics of a distribution circuit loaded with many induction motors and subjected to sudden changes in voltage at the beginning of the circuit. As opposed to earlier work by Duclut et al. [Phys. Rev. E 87, 062802 (2013)], the motors are disordered, i.e., the mechanical torque applied to the motors varies in a random manner along the circuit. In spite of the disorder, many of the qualitative features of a homogeneous circuit persist, e.g., long-range motor-motor interactions mediated by circuit voltage and electrical power flows result in coexistence of the spatially extended and propagating normal and stalled phases. We also observed a new phenomenon absent in the case without inhomogeneity or disorder. Specifically, the transition front between the normal and stalled phases becomes somewhat random, even when the front is moving very slowly or is even stationary. Motors within the blurred domain appear in a normal or stalled state depending on the local configuration of the disorder. We quantify the effects of the disorder and discuss the statistics of distribution dynamics, e.g., the front position and width, total active and reactive consumption of the feeder, and maximum clearing time.

Interfacial evaluation and hydrophobicity of multi-functional Ni-nanopowder/epoxycomposites for self-sensing and actuation

Electrical and interfacial properties of Ni-nanopowder/epoxy composites were investigatedfor self-sensing and actuation. Contact resistance and electrical resistivity were measuredusing a micro-specimen with a gradient grid of electrical contact on its length. Thespecimens’ self-sensing characteristics were monitored reasonably well under applied cyclicloading. Actuation in an electromagnetic field was evaluated by measurement of inducedstrain for three wavefunction voltages, i.e. sine, triangular and square. Due to the presenceof hydrophobic domains on the heterogeneous surface, the static contact angleof Ni-nanopowder/epoxy composites exhibited hydrophobicity. The specimensresponded well in both self-sensing and actuation tests, in electromagnetic fields,due to the intrinsic metallic property of Ni-nanopowder. Displacement of theactuator was evaluated to attain optimum performance as functions of wave type,frequency and voltage. The strain response followed the shape of the applied voltagesbetter, and was much smoother and less erratic for applied voltages with sine andtriangular waveforms than it was for voltages with a rectangular waveform. This isattributed to the sudden changes in voltage in the latter case. Such self-sensing andactuation, in conductive Ni-nanopowder/epoxy composites, might find uses inmulti-functional composite devices such as biomimetic and micro-size generators.