Large Peak Currents Research Articles

State‐space analysis based pole‐to‐ground line fault isolation strategy for LCC–HVDC systems

The common way to isolate the line fault in line-commutated converter-based high-voltage direct current (LCC-HVDC) transmission grids is regulating the trigger angle of converters on both terminals of the faulted line, which usually depends entirely on the conventional controller and goes with large current peak and lengthy overcurrent duration. In this study, a trigger-angle setting approach with adaptability is, therefore, proposed to provide a theoretical basis for the generation of fault isolation strategies under different scenarios. First, equivalent circuits of solid pole-to-ground line faults at rectifier and inverter terminals are established, and time-domain expressions of the fault and converter currents are obtained. Secondly, based on the analysis of current characteristics, the non-linear programming method is utilised to obtain the optimal trigger-angle sequence after the fault, which can be applied in the following fault isolation. Finally, the proposed approach is verified via power systems computer aided design (PSCAD)/electromagnetic transients including DC (EMTDC) simulation. The results show that it can effectively reduce the current peak and the overcurrent duration of the converter, which is of positive significance for maintaining the power system security and stability.

Electrochemical sensor based on conductive polyaniline coated hollow tin oxide nanoparticles and nitrogen doped graphene quantum dots for sensitively detecting dopamine

The hollow tin(IV) oxide (SnO2) nanoparticles prepared using a simple hydrothermal synthesis were served as a core for the fabrication of SnO2/polyaniline (PANI) nanocomposites using in situ chemical oxidative polymerization. The chemical and structure of the nanocomposites were characterized using Fourier transform infrared, X-ray diffraction, and transmission electron microscopy. The nanocomposites were then coated with nitrogen doped graphene quantum dots (N-GQDs) obtained by hydrothermal synthesis through electrostatic interaction. The catalytic behavior of nanocomposites modified glass carbon electrode towards dopamine (DA) has been investigated by electrochemical impedance spectroscopy (EIS), cyclic voltammetry and differential pulse voltammetry. The EIS test for prepared SnO2/PANI/N-GQD nanocomposites shows the very low charge-transfer resistance. The electrochemical performance of SnO2/PANI/N-GQD nanocomposites present the large peak currents, indicating the nanocomposites reveal better electrochemical activity of the presence of N-GQD. The SnO2/PANI/N-GQD nanocomposites contained linear response of detecting DA in the concentration range of 5 × 10−7–2 × 10−4 M with detection limit 2.2 × 10−7 M (S/N = 3). The fabricated nanocomposites also show excellent determination of DA at the presence of a mixture of l-ascorbic acid and uric acid. Because of the excellent electrochemical performance obtained in this report, we believe that the SnO2/PANI/N-GQD nanocomposites will be a promising biosensor material for the detection of dopamine.

Temperature-induced amperometric glucose biosensor based on a poly(N-vinylcaprolactam)/graphene oxide composite film.

A temperature-induced sensing film consisting of poly(N-vinylcaprolactam) (PVCL), graphene oxide (GO) and glucose oxidase (GOD) was fabricated and used to modify a glassy carbon electrode (GCE). The PVCL/GO/GOD/GCE composite film was characterized by electrochemical impedance spectroscopy (EIS). The morphological properties of the composite were investigated by scanning electron microscopy (SEM). The direct electron transfer (DET) of GOD was achieved. GOD at PVCL/GO/GOD/GCE exhibited a couple of well-defined redox peaks with a formal potential of -0.432 V (vs. Ag/AgCl). The composite film showed temperature-induced catalytic activity towards glucose. Large peak currents were observed by amperometry at -0.39 V (vs. Ag/AgCl) when the temperature was above the lower critical solution temperature (LCST) of PVCL, and then disappeared when it was below the LCST. The modified electrode displayed an excellent electrocatalytic response to glucose. The detection of glucose with the composite film ranged from 0.1 to 1.7 mmol L-1 above 35 °C. The constructed biosensor also possesses good stability, reproducibility and anti-interference ability.

An anti-passivation ink for the preparation of electrodes for use in electrochemical immunoassays.

p-Nitrophenylphosphate (PNPP) is usually employed as the substrate for enzyme-linked immunosorbent assays. p-Nitrophenol (PNP), the product of PNPP, with the catalyst alkaline phosphatase (ALP), will passivate an electrode, which limits applications in electrochemical analysis. A novel anti-passivation ink used in the preparation of a graphene/ionic liquid/chitosan composited (rGO/IL/Chi) electrode is proposed to solve the problem. The anti-passivation electrode was fabricated by directly writing the graphene-ionic liquid-chitosan composite on a single-side conductive gold strip. A glassy carbon electrode, a screen-printed electrode, and a graphene-chitosan composite-modified screen-printed electrode were investigated for comparison. Scanning electron microscopy was used to characterize the surface structure of the four different electrodes and cyclic voltammetry was carried out to compare their performance. The results showed that the rGO/IL/Chi electrode had the best performance according to its low peak potential and large peak current. Amperometric responses of the different electrodes to PNP proved that only the rGO/IL/Chi electrode was capable of anti-passivation. The detection of cardiac troponin I was used as a test example for electrochemical immunoassay. Differential pulse voltammetry was performed to detect cardiac troponin I and obtain a calibration curve. The limit of detection was 0.05 ng/ml.

Predicting lightning sourced electromagnetic fields

Sferics used in audio-frequency magnetotellurics (AMT) for shallow conductivity-depth soundings (up to 400 m in a 1000 Ωm half-space at 1.5 kHz) are detected by global lightning networks, which catalogue the time and location of up to four million lightning strikes per day. Passive AMT surveys do not use source information, but rather assume that global lightning activity provides sufficient signal if data are acquired for long enough. This assumption not only limits survey productivity, but can also result in poor signal-to-noise ratios (S/N), particularly at dead-band frequencies (1.5–5 kHz). To increase S/N and survey productivity, we used lightning network data as a proxy for direct measurement of sferic source information. We carried out a Global Positioning System (GPS) synchronised AMT survey, and for each lightning strike in the catalogue we modelled earth-ionosphere waveguide propagation to accurately predict arrival time for every predicted sferic in our time series data. We extracted a window of data around each predicted sferic and stored these time series into a structured database with associated lightning network data, such as lightning peak current, polarity and geographical coordinates. Two examples from our sferic database show that lightning network data are accurate enough to predict amplitude and polarisation of sferics at our survey site. For large lightning peak current, we observed a strong correlation between source proximity and increased S/N, particularly at dead-band frequencies, which often correlate to induction scales pertinent to mineral exploration. Our findings establish an interconnected relationship between lightning network data and lightning sourced fields, introducing known source AMT.

Capacitor performance limitations in high power converter applications

High voltage low inductance capacitors are used in converters as HVDC-links, snubber circuits and sub model (MMC) capacitances. They facilitate the possibility of large peak currents under high frequent or transient voltage applications. On the other hand, using capacitors with larger equivalent series inductances include the risk of transient overvoltages, with a negative effect on life time and reliability of the capacitors. These allowable limits of such current and voltage peaks are decided by the ability of the converter components, including the capacitors, to withstand them over the expected life time. In this paper results are described from investigations on the electrical environment of these capacitors, including all the conditions they would be exposed to, thereby trying to find the tradeoffs needed to find a suitable capacitor. Different types of capacitors with the same voltage ratings and capacitances where investigated and compared a) on a component scale, characterizing the capacitors transient performance and b) as part of different converter applications, where the series inductance plays a role. In that way, better insight is achieved on how the capacitor construction can affect the total performance of the converter.

Application of Low-Cost Cu–Sn Bimetal Alloy as Oxygen Reduction Reaction Catalyst for Improving Performance of the Microbial Fuel Cell

ABSTRACTIn this experiment, a new bimetal low–cost Cu–Sn alloy was synthesized and it was tested as catalyst for oxygen reduction reaction (ORR) in MFC and the results were compared with the commercially available Pt-C catalyst. Cyclic voltammetry for evaluating ORR of the test cathode containing Cu-Sn catalysts under oxygen saturated environment displayed large ORR current peak, showing less overpotential demand for ORR. Maximum power density of 457 mW/m2 obtained from MFC using Cu–Sn catalyst, was found to be slightly higher than the power density of 446 mW/m2 demonstrated by MFC using Pt based cathode. Biochemical conversion of organic matter to direct electric current in Cu–Sn based MFC occurred at a coulombic efficiency of 55.8%, while demonstrating 92% of chemical oxygen demand removal. This study demonstrated application of low cost Cu–Sn bimetal alloy as excellent ORR catalyst in MFC and would be very helpful to commission larger MFCs for field applications to harvest energy in the form of direct electricity from wastewaters while offering wastewater treatment.

Switched voltammetric determination of ractopamine by using a temperature-responsive sensing film.

This study describes an electrochemical sensor for the animal growth promoter ractopamine. The method is based on the use of a glassy carbon electrode (GCE) modified with a temperature-responsive sensing film composed of reduced graphene oxide, C60 fullerene, and the temperature-sensitive polymer poly(2-(2-methoxyethoxy)ethyl methacrylate) (PMEO2MA). The modified GCE was characterized by scanning electron microscopy and electrochemical impedance spectroscopy. A large oxidation peak current can be observed (maximum typically at 0.57V vs. Ag/AgCl) when the temperature is raised to above the lower critical solution temperature of PMEO2MA. This peak disappears at lower temperature. Under optimum conditions, the sensor has a detection range for ractopamine from 0.1 to 3.1μM, with an 82nM detection limit. The method was successfully applied to the determination of ractopamine in spiked pork samples. Graphical abstract Schematic presentation of the reversible, temperature-controlled "on/off" electrochemical behavior of ractopamine at a glassy carbon electrode modified with a film composed of reduced graphene oxide (rGO), C60 fullerene and the poly(2-(2-methoxyethoxy)ethyl methacrylate) (PMEO2MA).

Temperature-responsive multifunctional switchable nanoreactors of poly (N-isopropylacrylamide)/SiO2/lanthanide-polyoxometalates/Au: Controlled on/off catalytic and luminescent system

A method was developed for the preparation of temperature-responsive multifunctional nanoreactor by coating the poly (N-isopropylacrylamide) (PNIPAM) on the external surface of silica/lanthanide-POMs/Au spheres. The nanoreactor showed the repeated on/off catalytic activity and switchable luminescence by temperature stimuli. For example, the nanocomplexes showed strong red luminescence in solution and excellent catalytic activity in the reduction of 4-nitrophenol at 25°C. However, when the temperature was 40°C, the red luminescence almost disappeared in solution and catalytic activity was sharply decreased. Moreover, in solutions of K4Fe(CN)6 containing Na2SO4 at 25°C, it demonstrated the well-defined cyclic voltammograms (CV) peaks with large peak currents, showing the “on” state; at 40°C, the CV response was significantly suppressed, showing the “off” state. The smart nanoreactors have great potential for applications in many fields, such as bio-materials, controlled labeling catalysis, switches and so on.

Control of current distribution between parallel‐connected NTC thermistors

At power turn-on in electronic equipments, a large current peak is observed due to large capacitance in the circuit. This current peak can be avoided by inserting negative temperature coefficient (NTC) thermistors. A new design of high-reliability, lowcost NTC thermistors is tried. Parallel connection of the thermistors is investigated, where the thermistors were thermally connected by ceramic package. It is shown that the thermal connection between the thermistors plays an important role in current distribution.

Design & Simulation of PV Grid system with Dispatchable Supercapacitor

This paper presents a reliable, extended range power storage for grid connected PV systems. The power supply consists of solar PV source, a battery and Super capacitor (SC). Main source of power is battery, and is connected with super capacitor. These are connected at the starting and transient phase like overloading. Photovoltaic cell works for the steady condition. The total effect of such arrangement is to improve travel range, reduced size of battery , enhanced excellent response during overloading condition and improved battery life .Better performance which gives optimal use of energy, smooth ride and minimum size of sources of energy. Many stand-alone photovoltaic systems need storage device for providing steady state energy to the load when photovoltaicirradiation is not sufficient. Generally, Batteries are used for such application. Thus, providing a large peak current, like starting of motor, degrades plates of battery, results in devastation of battery. An alternate solution of providing heavy current is to connect battery with super capacitors forming an hybrid energy storage system, for which battery could provide steady state energy also the super capacitor can provide the peak power to connected load. A secondary source, solar panel module is available to charge battery and super capacitor.

Temperature-responsive amperometric H2O2 biosensor using a composite film consisting of poly(N-isopropylacrylamide)-b-poly (2-acrylamidoethyl benzoate), graphene oxide and hemoglobin

A temperature-responsive biosensing film consisting of the temperature-responsive block co-polymer poly (N-isopropylacrylamide)-b-poly(2-acrylamidoethyl benzoate) (referred to as PNIPAM-b-PAAE), graphene oxide (GO), and hemoglobin (Hb) was fabricated and used to modify a glassy carbon electrode (GCE). The film provides a favorable micro-environment for Hb to facilitate the electron transfer to the GCE. Hb at PNIPAM-b-PAAE/GO/Hb (PGH) film exhibits a couple of well-defined redox peaks with a formal potential of −0.371 V (vs. SCE) and displays intrinsic electro-catalytic activity toward H2O2. The sensing film also shows temperature-tunable catalytic activity toward H2O2 that can be stimulated by temperature. Large peak currents can be seen in amperometry at 0.4 V (vs. SCE) in pH 7.0 phosphate buffer only if the temperature is above the lower critical solution temperature (LCST) of 32 °C. The response of the modified GCE is linear in the 0.1 to 3.7 μmol L−1 concentration range if operated at above 32 °C, but in the 0.2 to 3.7 μmol L−1 concentration range at below 30 °C. This behavior is attributed to the temperature-dependent phase transition of PNIPAM-b-PAAE and cooperative effect of GO. The strategy presented here in our perception meets the requirements of switchable sensors for use in bioscience and biotechnology.

Scaling magnetized liner inertial fusion on Z and future pulsed-power accelerators

The MagLIF (Magnetized Liner Inertial Fusion) concept [S. A. Slutz et al., Phys. Plasmas 17, 056303 (2010)] has demonstrated fusion–relevant plasma conditions [M. R. Gomez et al., Phys. Rev. Lett. 113, 155003 (2014)] on the Z accelerator with a peak drive current of about 18 MA. We present 2D numerical simulations of the scaling of MagLIF on Z as a function of drive current, preheat energy, and applied magnetic field. The results indicate that deuterium-tritium (DT) fusion yields greater than 100 kJ could be possible on Z when all of these parameters are at the optimum values: i.e., peak current = 25 MA, deposited preheat energy = 5 kJ, and Bz = 30 T. Much higher yields have been predicted [S. A. Slutz and R. A. Vesey, Phys. Rev. Lett. 108, 025003 (2012)] for MagLIF driven with larger peak currents. Two high performance pulsed-power accelerators (Z300 and Z800) based on linear-transformer-driver technology have been designed [W. A. Stygar et al., Phys. Rev. ST Accel. Beams 18, 110401 (2015)]. The Z300 design would provide 48 MA to a MagLIF load, while Z800 would provide 65 MA. Parameterized Thevenin-equivalent circuits were used to drive a series of 1D and 2D numerical MagLIF simulations with currents ranging from what Z can deliver now to what could be achieved by these conceptual future pulsed-power accelerators. 2D simulations of simple MagLIF targets containing just gaseous DT have yields of 18 MJ for Z300 and 440 MJ for Z800. The 2D simulated yield for Z800 is increased to 7 GJ by adding a layer of frozen DT ice to the inside of the liner.

Reversible Switched Detection of Dihydroxybenzenes Using a Temperature-sensitive Electrochemical Sensing Film

A composite sensing film (PGS), consisting of poly(N-isopropylacrylamide)101-b-poly(2-acrylamidoethyl benzoate)37 (PNIPAM101-b-PAAEB37), graphene oxides (GO) and short multi-walled carbon nanotubes (SMWCNs), was fabricated and modified onto a working electrode. The sensing film served as a reversible switch for electrochemical detection, with the switching behaviour responding to thermal stimuli. Cyclic voltammetry of hydroquinone (HQ) and catechol (CC) at the PGS film-modified electrode displayed large peak currents when the temperature was above the lower critical solution temperature (LCST) of PNIPAM101-b-PAAEB37. These large currents disappeared at low temperature. Interestingly, the composite film showed reversed electrochemical “on/off” behaviour as compared to previously reported switchable electrodes, which were modified only with temperature-responsive polymers. This behaviour can be attributed to the temperature-dependent phase transition of PNIPAM101-b-PAAEB37 and cooperative effects of the other two functional components (SMWCNs and GO). The repeatable “on/off” switching of the voltammetric responses of HQ/CC on the PGS-modified electrode were achieved via regulating the solution temperature. This research provides a new type of temperature-controlled switchable electrode with potential applications in the design of novel sensors, fuel cells and electronics.

Enhanced oscillatory rectification and negative differential resistance in pentamantane diamondoid-cumulene systems.

We propose a new functionality for diamondoids in nanoelectronics. Based on the nonequilibrium Green's function formalism and density functional theory, we reveal that when attached to gold electrodes, the pentamantane-cumulene molecular junction exhibits large and oscillatory rectification and negative differential resistance (NDR) - depending on the number of carbon atoms in cumulene (Cn). When n is odd rectification is greatly enhanced where the rectification ratio can reach ∼180 and a large negative differential resistance peak current of ∼3 μA. This oscillatory behavior is well rationalised in terms of the occupancy of the carbon 2p states in Cn. Interestingly, different layers of C atoms in the pentamantane molecule have different contributions to transmission. The first and third layers of C atoms in pentamantane have a slight contribution to rectification, and the fifth and sixth layers have a stronger contribution to both rectification and NDR. Thus, our results suggest potential avenues for controlling their functions by chemically manipulating various parts of the diamondoid molecule, thus extending the applications of diamondoids in nanoscale integrated circuits.

Simultaneous determination of hydroquinone and catechol based on three-dimensionally ordered macroporous polycysteine film modified electrode

A three-dimensionally ordered macroporous (3DOM) polycysteine (PCE) film was electropolymerized on the glassy carbon electrode (GCE) using polystyrene spheres as template. The electrochemical behaviors of hydroquinone (HQ) and catechol (CC) were studied, and two independent oxidation peaks were observed. Compared with the bare GCE and GCE modified with PCE without using template, this electrode displays larger peak currents which may be attributed to the structure of PCE and the large surface area of the nanopore array structure. As a result, a novel electrochemical method was developed for the simultaneous determination of HQ and CC. Under the optimized conditions, the peak currents were linear to concentrations in the wider ranges of 9 to 700 μM for HQ and from 3 to 700 μM for CC. The method was successfully applied to the simultaneous determination of HQ and CC in spiked water samples, and the results are satisfactory.

A Novel Flux Weakening Control Strategy for Permanent Magnet Actuator of Vacuum Circuit Breaker

Traditional vacuum circuit breaker (CB) equipped with a bistable permanent-magnet (PM) actuator suffers from the disadvantages of having long start-up time and large current peak, and these shortcomings are limiting its applications on synchronization operation and high-voltage switchgear. In this paper, a new drive circuit which can significantly weaken the flux of the holding force with the usage of an auxiliary capacitor is proposed. In the proposed circuit, a negative current is circulated in the respective coil when the PM actuator is ready to switch on or off . Cosimulation which integrates the PM actuator and the circuit is carried out with the Maxwell and Simplorer software. The prototype is tested on the platform in conjunction with a 10-kV PM vacuum CB (VCB) to showcase the success of the proposed flux-weakening control strategy.

Evaluation of Hydrophilized Graphite Felt for Electrochemical Heavy Metals Detection (Pb2+, Hg2+)

Hydrophilized graphite felt has been used,for the first time, for the electrochemical detection of Hg2+ions both as single metal species and via its simultaneous detection with Pb2+. To do so, square wave voltammetry (SWV) method was developed with alginate modified graphite felt as working electrode. The structure of the graphite felt such as its high porosity and specific surface area coupled with its good electrical conductivity allows achieving large peak currents via the SWV method, suggesting that the alginate coating helps to preconcentrate metals at the carbon surface. The as-described electrode has low cost, it is easy to manipulate, and the electrochemical analysis can be performed by simple immersion of the felt in the metal solution.

A facile one-step in situ synthesis of copper nanostructures/graphene oxide as an efficient electrocatalyst for 2-naphthol sensing application

A copper nanostructures-graphene oxide (Cu/GO) hybrid as a new electrocatalyst for highly sensitive detection of 2-naphthol (2-NAP) was successfully synthesized by a one-pot and in situ chemical reduction approach. The characterization results reveal that the cubic Cu nanostructures are tightly attached onto the GO sheets in the resulting hybrid. A lower oxidation potential and a larger peak current were observed for the 2-NAP oxidation at the Cu/GO modified electrode, demonstrating the synergistic electrocatalysis from Cu nanostructures and GO sheets. Consequently, the Cu/GO hybrid exhibits a low detection limit (5.0nM) and wide linear ranges (0.1–4.0μM and 4.0–130.0μM) when used as a sensing material for the sensitive detection of 2-NAP. Finally, the fabricated sensor was successfully applied in the detection of 2-NAP in real samples and satisfactory recoveries in the range of 99.3%–104.0% were achieved.

Thermo- and Sulfate-Controllable Bioelectrocatalysis of Glucose Based on Horseradish Peroxidase and Glucose Oxidase Embedded in Poly(N,N-diethylacrylamide) Hydrogel Films

Dual-responsive poly(N,N-diethylacrylamide) (PDEA) hydrogel films with entrapped horseradish peroxidase (HRP) and glucose oxidase (GOD) were successfully prepared on electrode surface with a simple one-step polymerization procedure under mild conditions, designated as PDEA-HRP-GOD. Cyclic voltammetric (CV) response of electroactive probe K3Fe(CN)6 at the film electrodes displayed reversible thermo- and sulfate-responsive switching behavior. For example, at 25°C, the K3Fe(CN)6 demonstrated a well-defined CV peak pair with large peak currents for the films, showing the on state, while at 40°C, the CV response was greatly suppressed and the system was at the off state. The influence of temperature and Na2SO4 concentration on the switching behavior of the film system was not independent or separated, but was synergetic. The responsive mechanism of the system was ascribed to the structure change of PDEA component in the films with temperature and sulfate concentration. This switching property of the PDEA-HRP-GOD films could be further used to realize dual-responsive catalytic oxidation of glucose sequentially by HRP and GOD entrapped in the films with Fe(CN)6 (3-) as the mediator through changing the surrounding temperature and Na2SO4 concentration. This system may establish a foundation for fabricating a new type of multi-switchable electrochemical biosensors based on bienzyme electrocatalysis.