Search

Recent advancements on the development of nonprecious electrocatalysts with iron (Fe) incorporated active centers have generated confidence on realizing cost-effective proton exchange membrane fuel cells (PEMFCs). However, most of these catalysts that emerged as a substitution for the platinum supported on carbon (Pt/C) catalysts in oxygen reduction reaction (ORR) are active under basic conditions, and their feasibility in PEMFCs remains as a challenge. In this scenario, this work reports the synthesis of a Pt-free oxygen reduction electrocatalyst prepared by the annealing of polydopamine grown melamine foam. The prepared catalyst has a three-dimensional (3D) interconnected bilayer network structure possessing the carbon nitride backbone wrapped by graphitic carbon layer bearing iron carbides and nitrides as the active centers (3D-FePDC). Interestingly, the 3D-FePDC catalyst displayed an ORR activity both under acidic and basic conditions. Whereas the ORR performance of 3D-FePDC closely matches that of the commercial Pt/C in the basic medium, it displays only a low overpotential value of 60 mV under acidic conditions compared to its Pt counterpart. The kinetics of ORR on 3D-FePDC is found to be similar to the four-electron (4e) reduction pathway displayed by Pt/C. Testing of a PEMFC in a single cell mode by using 3D-FePDC as the cathode catalyst and Nafion membrane delivered a maximum power density of 278 mW cm -2 , which is a promising value expected from a system based on the nonprecious metal cathode. Ultimately, as a cost-effective catalyst that can effectively perform irrespective of the pH conditions, 3D-FePDC offers significant prospects in the areas like fuel cells and metal-air batteries which work in acidic and/or basic conditions.

Ni- and Co-based materials have of late gained prominence over conventional noble metal-based ones as catalysts for energy devices. Here, a high performance catalyst which can facilitate both the oxygen evolution reaction (OER) and oxygen reduction reaction (ORR) was developed by anchoring a NiCo 2 O 4 nanowire array on a carbon nanotube sponge (NCS). The three-dimensional morphology of NCS ensured efficient transport of the reactants and products on the catalyst surface, thereby improving the activity of the material. The prepared catalyst showed remarkable OER activity, requiring an overpotential of 280 mV, which is comparable to that of noble-metal catalysts. In addition to the noteworthy OER performance, the catalyst performed well with respect to the ORR. The total oxygen electrode activity overpotential of the catalyst was found to be 0.83 V, which is lower than that of commercial electrodes such as Pt/C and RuO 2 . A rechargeable Zn-air battery constructed with NCS had an open circuit voltage of 1.42 V, a maximum power density of 160 mW cm -2 , and an energy density of 706 W h kg -1 . NCS exhibited bifunctional electrocatalytic activity and high stability for both the OER and ORR, proving to be a good replacement for noble metal electrodes in rechargeable metal-air batteries., Competing Interests: There are no conflicts to declare., (This journal is © The Royal Society of Chemistry.)

We introduce a new and naturally abundant mild reducing agent, tannic acid, to improve the seed-mediated growth method for the synthesis of elongated tetrahexahedral Au nanocrystals enclosed with high-index (730) planes, at room-temperature. The control of the dimensions, plasmonics and electro-catalysis of such high-index faceted nanocrystals is remarkable.

Layer-separated 3D nitrogen doped graphene (NG) with an accessible interstitial surface and modulated activity characteristics for oxygen reduction in acidic medium could be prepared by wrapping NG sheets on in situ generated carbon nitride (CNx) tetrapods.

An accurate fault location estimation (FLE) helps in quick power system restoration in the event of transmission lines exposed to faults. However, the accuracy of FLE gets affected in shunt FACTS-compensated system. Therefore, it is indispensable to develop an efficient FLE algorithm which serves the purpose of accurate estimation of fault location in shunt-compensated system. Consequently, this paper proposes a traveling wave-based FLE algorithm utilizing short-time matrix pencil method (STMPM) to estimate the fault location in the aforementioned system. In the proposed algorithm, STMPM is used to decompose windowed signal into time-indexed complex frequencies. From the fact that damping factors extracted from complex frequencies are near or equal to zero when the arriving traveling waves after inception of fault are at the middle of sliding window, the arrival time of waves is estimated and fault location is obtained. The efficacy of the proposed algorithm is tested on 100 MVAR STATCOM-compensated 500 kV transmission system under several fault scenarios and diverse operating conditions. The performance of STMPM-based FLE algorithm is compared with that of the existing methods and found to be more robust and reliable. Further, real-time validation of the proposed algorithm is carried out in OPAL-RT environment. [ABSTRACT FROM AUTHOR]

In view of sensitivity, selectivity, and operating speed of the relay, the current differential technique is an alternative against overcurrent and distance-based techniques for long transmission line protection. Moreover, this technique has limited performance due to Line Charging Capacitive Current (LCCC), Current Transformer (CT) saturation further, by using synchronized data, the effect of LCCC can be nullified. However, in case of synchronition is lost, the performance of the current differential is not reliable. Hence, in this paper, the Inverse of Difference of both end Current phasors (IDC) is applied to prevent maloperation due to channel delay and synchronization loss. The simulation experiments are conducted under various operating conditions on a 345 kV, 50 Hz, IEEE 39-bus network using PSCAD 4.5 and MATLAB (R2020a). Results reveal the enhanced security under CT saturation, LCCC and sensitivity under high resistance line to ground faults. [ABSTRACT FROM AUTHOR]

Summary: Catalyst layer (CL) is the most important component in the high‐temperature proton exchange membrane fuel cell (HT‐PEMFC), as it offers reaction sites for hydrogen oxidation reaction (HOR) and oxygen reduction reactions (ORR). As the electrochemical reactions take place at gas/electron/proton interface, the length of this triple‐phase boundary (TPB) in the CL governs the rate of electrochemical reactions. As the TPB in the HT‐PEMFC has not been studied yet, a numerical non‐isothermal 3D model and a percolation micro model were developed in this work to investigate the effect of CLs' properties on both the TPB length and cell performance. The volume fractions, particle size, and particle size ratio of ionomer and Pt/C were selected for optimization. The results show that peak current density could be achieved at an ionomer volume fraction of 52%. Further improvement of cell performance requires smaller particle size and smaller particle size ratio of ionomer. Novelty statement: A three‐dimensional non‐isothermal model of HT‐PEMFC was developed. By adopting the percolation model, length of triple phase boundary of HT‐PEMFC was successfully quantified. The particle parameters including the particle size and ionomer volume fraction can be optimized to increase the length of triple phase boundary, thus achieving higher cell performance. [ABSTRACT FROM AUTHOR]

This paper proposes an adaptive characteristic for eliminating the adverse effects of fault resistance and static synchronous compensator (STATCOM) on the performance of distance relays in transmission line and collector lines of doubly‐fed induction generator (DFIG)‐based wind farms in the case of single‐phase‐to‐ground resistive faults. The proposed method improves the performance in distance relaying and maintains the coordination between relay pairs in the transmission line and wind farm collector lines. In this method, an adaptive coefficient that can modify the zone settings of conventional distance relays is added to their characteristic to improve the accuracy and coordination under the mentioned conditions. Using analytical relationships and numerical results from simulations in Matlab/Simulink environment, the efficiency of the proposed method is confirmed. [ABSTRACT FROM AUTHOR]

In this paper, the localization issue associated with distance relay protecting a transmission line with static synchronous compensator (STATCOM) is discussed. Generally, distance relay is mal-operated due to the dynamic behaviour of STATCOM during its inductive and capacitive modes of operation. Because, STATCOM operation creates the problem of correct measurement of fault distance and is responsible of under-reach and over-reach of distance relay. Furthermore, high fault resistance is also the reason of under-reach along with STATCOM operation. To overcome aforementioned challenges, an adaptive wide-area backup protection scheme (WABPS) is addressed which compares the calculated impedance and referenced impedance. Calculated impedance is the difference between impedance measured by relay and impedance contributed by fault resistance. Referenced impedance is the sum of fault impedance and impedance contributed by STATCOM. If calculated impedance is less than referenced impedance, then the relay will generate a trip signal. Proposed WABPS is inherent directional and provides information about fault detection, fault distance, and fault resistance during dynamic operation of STATCOM. The performance of the proposed WABPS is evaluated using technology of synchronize phasor measurement and communication channel. A 230 kV, 50 Hz system with a 24-pulse STATCOM is simulated and validated using PSCAD/EMTDC software package. [ABSTRACT FROM AUTHOR]

We report here a simple microwave irradiation method (850 W, 3 min) for the synthesis of palladium nanoparticles (Pd NPs) using ascorbic acid (as reducing agent) and sodium alginate (as stabilizer agent). The synthesized nanoparticles were characterized using transmission electron microscopy (TEM), energy dispersive X-ray (EDX), X-ray diffraction spectroscopy (XRD), UV-Visible spectroscopy, and Fourier transform infrared spectroscopy (FTIR) techniques. Antioxidant properties and cytotoxic effects of as-synthesized Pd NPs and Pd (II) acetate were also assessed. UV-Vis study showed the formation of Pd NPs with maximum absorption at 345 nm. From TEM analysis, it was observed that the Pd NPs had spherical shape with particle size distribution of 13–33 nm. Based on DPPH radical scavenging activity and reducing power assay, the antioxidant activities of Pd NPs were significantly higher than the Pd (II) acetate (p < 0.05). At the same concentration of 640 μg/mL, the scavenging activities were 32.9 ± 3.2% (Pd (II) acetate) and 27.2 ± 2.1% (Pd NPs). For A549 cells treated 48 h with Pd NPs, Pd (II) acetate, and cisplatin, the measured concentration necessary causing 50% cell death (IC50) was 7.2 ± 1.7 μg/mL, 32.1 ± 2.1 μg/mL, and 206.2 ± 3.5 μg/mL, respectively. On HSkMC cells, the IC50 of the Pd NPs (320 μg/mL) was higher compared to Pd (II) acetate (228.7 ± 3.6 μg/mL), which confirmed lower cytotoxicity of the Pd NPs. [ABSTRACT FROM AUTHOR]

Synthesis of highly efficient photocatalysts for energy and environment catalysis is still a big challenge in the materials field. Cadmium sulfide (CdS) is a promising visible light-driven photocatalyst, which can be composited with co-catalysts to increase its photo-activity and stability. In this study, a kind of graphene material with abundant structure defects (D-rGO) is synthesized by a two-step annealing process with nitrogen-doped rGO (N-rGO) as an intermediate. The high-temperature annealing could remove the doped heteroatoms to form structure defects with five or seven carbon atoms. The D-rGO is then used as co-catalyst for the modification of CdS nanoparticles, and enhanced photocatalytic activities could be obtained. A large hydrogen evolution rate of 102.7 μmol h−1 g−1 is achieved, which is also effective for 4-nitrophenol reduction with a rate constant of 0.168 min−1. The novel CdS/D-rGO composite contains no noble metals and could be used as multi-functional photocatalysts, thus should has great potential in the photocatalysis field. [ABSTRACT FROM AUTHOR]

In this paper, a rapid, easy and very efficient method for the synthesis of bis(pyrazolyl)methanes has been reported in the presence of nickel–guanidine complex immobilized on MCM-41 (MCM-41@Gu@Ni) as a recyclable nanocatalyst. This mesoporous silica catalyst was effective for the one-pot multi-component reaction of arylaldehydes, phenylhydrazine and ethyl acetoacetate in ethanol solvent. The current synthesis shows attractive features, for example the use of recoverable and reusable nanocatalyst (5 times), easy workup, suitable one-pot procedure, short reaction times, good to excellent yields and moderate reaction conditions. [ABSTRACT FROM AUTHOR]

Current transformers (CTs) with air gaps in their iron cores are mainly applied in power systems to prevent saturation‐caused malfunctions of current‐based relays. However, performing reliable power system studies necessitates accurate modeling of air‐gapped CTs. This paper presents a new model for air‐gapped CTs based on the Preisach Theory, which has the ability to represent the role of air gaps of different lengths in the performance of a CT. The salient feature of this study in comparison with other published works is that it does not require measuring the magnetization curves of the air‐gapped core, which is often difficult. In order to validate the effectiveness of the proposed method, several simulations have been performed using PSCAD/EMTDC and MATLAB software packages. Simulation results indicate that the proposed model can accurately represent the characteristics of saturation as well as remanence of air‐gapped CTs. © 2018 Institute of Electrical Engineers of Japan. Published by John Wiley & Sons, Inc. [ABSTRACT FROM AUTHOR]

The shunt flexible AC transmission system devices affect the protection schemes because of reactive power injection. Therefore, robust protection schemes are required. This study presents a fault detection scheme, which is based on estimated reactive power factor (ERF) and differential current with modified setting. The ERF is defined as sine of phase difference between the static synchronous compensator tap voltage and differential current. The static synchronous compensator tap voltage can be estimated using local end voltage and current. The ERF is measured at both the relay ends. In capacitive mode, if both ERFs are more than upper threshold, the fault is external, and if any ERF is less than upper threshold, the fault is internal. In inductive mode, if ERF is between upper and lower threshold, fault is internal else, if differential current is more than modified differential current setting, the fault is internal, or else, the fault is external. The performance of presented scheme is investigated for various system configurations with PSCAD/EMTDC simulations. Further, the scheme is successfully validated in real-time digital simulator. It is found that the scheme is robust and selective for various faulty conditions, compensation level variations, and location variations. [ABSTRACT FROM AUTHOR]

The increasing penetration of flexible AC transmission system devices and renewable generation resources within existing conventional power system networks has necessitated the relook into protective relaying schemes for ensuring grid security and integrity. This paper investigates the impact of a unified power flow controller (UPFC) on Zones 1 and 2 (with infeed current) of the conventional distance relay and pilot protection schemes. Using both analytical and detailed simulation techniques, these schemes have been very thoroughly assessed. The protection impacts for four functions of UPFC are compared with each other comprehensively. The infeed current effect for existing distance relay, as represented by standard MHO characteristics, has been adapted to factor the effect of source and line impedances. In addition, a proposed modification procedure highlights the main reasons for the impedance trajectory changes during faults at Zones 1 and 2 resulting due to the presence of the UPFC. A detailed model of UPFC and six measuring units of distance protection have been developed in the MATLAB/Simulink environment. The accuracy of compensated network and impedance measuring units are verified using Opal-RT's RT-LAB real-time engineering emulator. Copyright © 2016 John Wiley & Sons, Ltd. [ABSTRACT FROM AUTHOR]

Dimensioning a current transformer (CT) is one of the most important tasks during the substation planning process. The installation of a correctly specified CT will ensure the integrity of the protection scheme. However, some parameters required for dimensioning a CT can be obtained only after the CT is installed in the substation. Because of the conflicting requirements, utility companies commonly adopt a simplified approach in compensating for the missing parameters. Two other methods for dimensioning CT under the given constraint during the planning stage have also been proposed by several authors. In view of the availability of the three methods of approximating CT specifications, this paper will conduct a comparative study to evaluate their accuracies. The approximated specifications of the CT during the planning stage are compared against those measured from a practical substation. Based on the findings from the comparative studies, the most reliable approach for CT dimensioning during the planning stage is proposed. © 2016 Institute of Electrical Engineers of Japan. Published by John Wiley & Sons, Inc. [ABSTRACT FROM AUTHOR]

Current differential protection is widely used in transmission line due to its inherent simplicity and good performance. In order to strive to increase sensitivity of protection without compromising stability on external faults, phase correlation current differential protection is presented in this paper. Current phase difference is introduced to the differential current principle so as to improve the sensitivity and reliability of differential protection simultaneously. Comprehensive analysis and comparisons of performance characteristics in Alpha Plane demonstrate that phase correlation current differential protection has preferable performance than that of conventional current differential protection. As far as CT saturation is concerned, the proposed protection scheme has flexible adaptability to ensure significant improvement in sensitivity and dependability for internal faults while still improving stability for external faults. The performance of the proposed protection is investigated for various faults of transmission line simulated by Electro-Magnetic Transients Program including DC and record fault data from real power system. The test results show that the proposed protection has satisfactory operation performance. Copyright © 2013 John Wiley & Sons, Ltd. [ABSTRACT FROM AUTHOR]

This paper demonstrates a systematic and objective approach for dimensioning of current transformers (CT) for biased differential relay. The paper proposes some mathematical formulae which allow protection engineers to dimension CT for meeting requirements imposed by sensitivity, and yet maintain stability for through fault. The formulae can be extended to CT with antiremanence magnetic paths. The suitability for the method is demonstrated for various sensitivity objectives and system conditions. The paper also discusses the implementation for different measurement algorithms. [ABSTRACT FROM AUTHOR]

With respect to sensitivity, selectivity and speed of operation, the current differential scheme is a better way to protect transmission lines than overcurrent and distance-based schemes. However, the protection scheme can be severely influenced by the Line Charging Capacitive Current (LCCC) with increased voltage level and Current Transformer (CT) saturation under external close-in faults. This paper presents a new UHV/EHV current-based protection scheme using the ratio of phasor summation of the two-end currents to the local end current, instead of summation of the two-end currents, to discriminate the internal faults. The accuracy and effectiveness of the proposed protection technique are tested on the 110 kV Western System Coordinating Council (WSCC) 9-bus system using PSCAD/MATLAB. The simulation results confirm the reliable operation of the proposed scheme during internal/external faults and its independence from fault location, fault resistance, type of fault, and variations in source impedance. Finally, the effectiveness of the proposed scheme is also verified with faults during power swing and in series compensated lines. [ABSTRACT FROM AUTHOR]

Summary: The existence of midpoint series flexible alternating current transmission system (FACTS) devices leads to degrade the performance of mho relay, leading in erroneous estimation of fault location, ie, overreach or underreach for wide variation in network parameters. This research article proposes a novel mho relay algorithm to improve the performance of distance relay in presence of FACTS device using phasor measurement unit (PMU). First, the complete model of transmission system employing static synchronous series compensator (SSSC) and its control strategy is described analytically, where the error introduced in measurement of impedance due to SSSC on the performance of distance relay. Second, a novel mho relay procedure is developed based on PMU to protect the first zone of double‐circuit transmission line for single line‐to‐ground (SLG) fault. The proposed work is analysed and simulated with 48‐pulse SSSC carried out with Bergeron model of transmission line using power system computer‐aided design (PSCAD) computer simulation. Finally, the simulation results represent that the suggested adaptive scheme is truthful, reliable, and secure with change in compensation level of SSSC. [ABSTRACT FROM AUTHOR]

Summary: Saturation of the current transformer (CT) results in maloperation of current‐dependent protective relays. While enhancing in the core area may prevent the saturation, it simultaneously increases the size, the weight, and, subsequently, the price of the CT, which is desirable for neither the CT manufactures nor the operators. This paper conducts a probabilistic analysis to investigate the impact of influential factors on CT saturation for CT dimensioning. The main aim of the probabilistic analysis is to identify the busses of the power network in which they may be highly exposed to the CT saturation phenomena. The proposed probabilistic framework is performed based on the time‐domain fault analysis. In the probabilistic time‐domain fault analysis, the effects of fault location, fault type, and fault resistance are investigated. Also, the effects of load and generation are considered probabilistically. On the basis of the selected random variables (RVs), the probability density function (PDF) of the voltage of the knee point (VKP) is obtained. Also, a new criterion so‐called depth of saturation (DofS) is introduced that shows the level of exposure to saturation phenomena for each bus. The results show that the proposed probabilistic framework helps to find a general observation to VKP of each CT from the CT‐dimensioning aspect. Also, the proposed probabilistic framework provides some useful information about the probability of saturation area in the power system. [ABSTRACT FROM AUTHOR]

Summary: The use of series compensation in a transmission line with capacitors may result in new problems like torsional oscillations in shaft sections of turbine‐generator due to subsynchronous resonance (SSR) when system frequency matches with any one of torsional mode frequency of shaft system during fault or disturbances occur in the transmission line. The subsynchronous current due to SSR during fault also affects the reach of a distance protection system. The diminution of SSR is enhanced by series voltage injection into the power transmission line with static synchronous series compensator (SSSC) from the knowledge of subsynchronous components, extracted from the system. The use of SSSC in transmission line reduces the subsynchronous oscillations, but it adversely affects the distance protection system which leads to an imprecise assessment of fault location, ie, over or under‐reach. This paper investigates the SSR mitigation in the presence of SSSC and its effect on distance protection scheme. A new approach is proposed for mitigating the problems associated with distance protection by using the synchrophasor measurement. The entire study of simulation is investigated by using a 48‐pulse SSSC carried out with Bergeron model of transmission line in PSCAD. The simulation results represent that the suggested adaptive scheme is truthful, reliable, and secure with a change in compensation level of SSSC. [ABSTRACT FROM AUTHOR]