Anion exchange membrane (AEM)-equipped electrochemical cells can be used for removing the carbon dioxide (CO
2
) from biogas, thereby upgrading its energy content. The CO
2
absorbed in the catholyte ...can be transported across the AEM as (bi)carbonate and then recovered in the anodic chamber of the electrochemical cell. However, CO
2
regeneration in the anode chamber diminishes the oxygen (O
2
) content in the anodic gas stream. Given this electrochemically produced oxygen can have a high-industrial application value, such as for promoting more efficient biological wastewater treatment processes, we hereby proposed and validated a three-chamber electrochemical cell configuration capable of removing CO
2
and recovering it in an intermediate chamber, with a concomitant anodic generation of high-purity O
2
gas. Our prototype successfully facilitated CO
2
recovery in a separate chamber preventing CO
2
contamination of the anodic O
2
gas stream. Results also suggested that an approximately tenfold increase in CO
2
loading rate enhanced the relative CO
2
diffusion flux from 5 to 43% through the AEM, by lowering the catholyte pH as well as improving gas–liquid CO
2
transfer. A mathematical model was also developed to accurately predict the polarization performance of the electrochemical cell.
Graphical abstract
Subsynchronous resonance (SSR) damping in fixed-speed wind turbine generator systems (FSWTGS) by using two series flexible ac transmission system (FACTS) devices, the thyristor-controlled series ...capacitor (TCSC), and gate-controlled series capacitor (GCSC) are studied in this paper. The former is a commercially available series FACTS device, and the latter is the second generation of series FACTS devices using gate turnoff (GTO) or other gate-commuted switches. The GCSC is characterized by a fixed capacitor in parallel with a pair of antiparallel gate-commuted switches enabling rapid control of series impedance of a transmission line. It is shown that the SSR damping with a GCSC is limited to changing the resonance frequency, in comparison with a fixed capacitor, which may not be adequate to damp out the SSR. Therefore, a supplementary SSR damping controller (SSRDC) is designed for the GCSC. Moreover, it is proven that the GCSC equipped with a well-designed SSRDC can effectively damp the SSR in FSWTGS. In order to verify the effectiveness of the GCSC in SSR damping, its performance is compared with the TCSC, which is an existing series FACTS device. In addition, time-frequency analysis (TFA) is employed in order to evaluate and compare the SSR time-varying frequency characteristics of the GCSC and TCSC. The IEEE first benchmark model on SSR is adapted with an integrated FSWTGS to perform studies, and extensive simulations are carried out using PSCAD/EMTDC to validate the result.
This paper presents application and control of the gate-controlled series capacitor (GCSC) for series compensation and subsynchronous resonance (SSR) damping in doubly-fed induction generator ...(DFIG)-based wind farms. The GCSC is a new series FACTS device composed of a fixed capacitor in parallel with a pair of antiparallel gate-commuted switches. The study considers a DFIG-based wind farm, which is connected to a series-compensated transmission line whose parameters are derived from the IEEE first benchmark model for computer simulation of the SSR. The small-signal stability analysis of the system is presented, and the eigenvalues of the system are obtained. Using both modal analysis and time-domain simulation, it is shown that the system is potentially unstable due to the SSR mode. Therefore, the wind farm is equipped with a GCSC to solve the instability of the wind farm resulting from the SSR mode, and an SSR damping controller (SSRDC) is designed for this device using residue-based analysis and root locus diagrams. Using residue-based analysis, the optimal input control signal to the SSRDC is identified, which can damp the SSR mode without destabilizing other modes, and using root-locus analysis, the required gain for the SSRDC is determined. MATLAB/Simulink is used as a tool for modeling, design, and time-domain simulations.
This paper deals with subsynchronous resonance (SSR) phenomena in a capacitive series-compensated DFIG-based wind farm. Using both modal analysis and time-domain simulation, it is shown that the DFIG ...wind farm is potentially unstable due to the SSR mode. In order to damp the SSR, the rotor-side converter (RSC) and grid-side converter (GSC) controllers of the DFIG are utilized. The objective is to design a simple proportional SSR damping controller (SSRDC) by properly choosing an optimum input control signal (ICS) to the SSRDC block, so that the SSR mode becomes stable without decreasing or destabilizing the other system modes. Moreover, an optimum point within the RSC and GSC controllers to insert the SSRDC is identified. Three different signals are tested as potential ICSs including rotor speed, line real power, and voltage across the series capacitor, and an optimum ICS is identified using residue-based analysis and root-locus method. Moreover, two methods are discussed in order to estimate the optimum ICS, without measuring it directly. The studied power system is a 100 MW DFIG-based wind farm connected to a series-compensated line whose parameters are taken from the IEEE first benchmark model (FBM) for computer simulation of the SSR. MATLAB/Simulink is used as a tool for modeling and designing the SSRDC, and power system computer aided design/electromagnetic transients including dc (PSCAD/EMTDC) is used to perform time-domain simulation for design process validation.
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•Ultrasound-assisted oil extraction from Moringa peregrina seeds was studied.•The results show that sonication time and solvent amount are the key process variables.•Oil extraction ...increases with solvent-to-seed ratio and extraction time.•The ultrasound assisted oil extraction method enhances the oil yields by 10%.
In this paper, ultrasound-assisted extraction (UAE) of oil from Moringa peregrina seeds was studied and compared with the Soxhlet method. Based on the response surface methodology (RSM), the extraction process variables such as liquid-to solid ratio, ultrasound power, extraction time and temperature were investigated to achieve the highest yield. By screening these parameters, it was concluded that liquid-to-solid ratio (mL/g) and extraction time were the significant parameters for oil extraction from Moringa peregrina using ultrasound treatment. The best possible range for liquid-to-solid ratio (5–20 mL/g), extraction time (5–30 min), and optimum ultrasound power (348 W) as well as extraction temperature (30 °C) was obtained according to the single factor experiments. Afterward, the optimum process conditions which were determined by central composition design (CCD) to reach the maximum oil extraction yield (53.101%) were found to be 26.3 min for extraction time and 17.8 mL/g for liquid-to-solid ratio. In addition, the gas chromatography analysis and the physiochemical characteristics of oil extracts obtained through UAE and Soxhlet techniques including peroxide value (PV), antioxidant activity (DPPH%), total phenolic content (TPC), iodine value (IV), thermal stability, crystallization and melting behavior were determined and compared.
This paper first presents a step-by-step tutorial on modal analysis of a doubly-fed induction generator (DFIG)-based series compensated wind farm. The model of the system includes a wind turbine ...aerodynamics, a sixth-order order induction generator, a second-order two-mass shaft system, a fourth-order order series compensated transmission line, an eighth-order rotor-side converter (RSC) and grid-side converter (GSC) controllers, and a first-order DC-link model. Then, using modal analysis and time-domain simulations, it is shown that a fixed-series compensated DFIG is highly unstable due to the sub-synchronous resonance (SSR) mode. In order to damp the SSR mode, the wind farm is interfaced with the gate-controlled series capacitor (GCSC) - which is a new series flexible AC transmission system (FACTS) device. A SSR damping controller (SSRDC) is designed for the GCSC using residue-based analysis and root locus diagrams, and an effective input control signal (ICS) to the SSRDC is identified in order to simultaneously increase damping of both the SSR and super-synchronous (SupSR) modes. The IEEE first benchmark model on SSR is adapted with an integrated DFIG-based wind farm to perform studies. Matlab/Simulink is used as a tool for designing process, and PSCAD/EMTDC is used for time-domain simulations.
•Modelling of oxygen mass transfer from single bubbles to the water.•By 20% increase in mass transfer coefficient by replacing air bubbles with oxygen.•Using oxygen in activated sludge offsets energy ...usage of water electrolysis by 30%•Replacing air with oxygen in aquaculture provides 14 times higher energy efficiency.
One strategy to cut down the cost of hydrogen production by electrolysis is effective utilization of the byproduct oxygen. The oxygen can be used to replace the air in the aeration of wastewater in the activated sludge process, or in the aquaculture industry. To determine the benefit of replacing air with oxygen in the aeration process, an analytical simulation of a single bubble rising in stagnant water and a comparison with literature is established. Our results show up to 30 % energy return can be obtained by using oxygen in wastewater treatment by the activated process. The greater benefit of replacing air with pure oxygen in industries requiring higher dissolved oxygen such as the aquaculture industry is also presented.
High impedance fault detection: A review Ghaderi, Amin; Ginn, Herbert L.; Mohammadpour, Hossein Ali
Electric power systems research,
02/2017, Volume:
143
Journal Article
Peer reviewed
•A comprehensive and systematic survey of the literature of the high impedance fault (HIF) is presented.•HIF phenomenon is discussed and its physical and electrical aspects are studied.•The existing ...HIF detection techniques are evaluated and compared.•Other aspects of HIF such as its modelling and location are discussed.•Possible road to the future of the HIF is discussed.
Protection from the high impedance fault (HIF) has been one of the biggest challenges in the power distribution network. HIF typically occurs when the conductors in distribution network break and touch the ground surface; or lean and touch a tree branch. This fault, with current magnitude close to the load current level, is not detectable by over-current relays. This paper aims to review the literature related to the HIF phenomenon. In this work, the HIF detection techniques are categorized, evaluated, and compared with one another. Furthermore, the existing HIF models and HIF location techniques are reviewed. Finally, the shortcoming of the existing perspective toward the HIF phenomenon and the possible road to the future for HIF detection is discussed.
Using both modal analysis and time domain simulations, it is shown that sub-synchronous resonance (SSR) phenomena in a series-compensated DFIG wind farms may cause system instability. In order to ...damp the SSR, both the rotor-side converter (RSC) and grid-side converter (GSC) controllers of the doubly-fed induction generator (DFIG) are utilised. The objectives are to design an SSR damping controller (SSRDC) with an optimum input control signal (ICS), and to identify the optimum point within the RSC and GSC controllers where to introduce the SSRDC. The optimum ICS is identified using residue-based analysis and root-locus method. The criterion for choice of optimal ICS is that it should make the SSR mode stable without decreasing or destabilising the other system modes. Moreover, since the dynamics of the DFIG-based series compensated wind farm change with varying operating point conditions, the operation of the SSRDC is optimised using the adaptive gain-scheduling method.
A new high-impedance fault (HIF) detection method using time-frequency analysis for feature extraction is proposed. A pattern classifier is trained whose feature set consists of current waveform ...energy and normalized joint time-frequency moments. The proposed method shows high efficacy in all of the detection criteria defined in this paper. The method is verified using real-world data, acquired from HIF tests on three different materials (concrete, grass, and tree branch) and under two different conditions (wet and dry). Several nonfault events, which often confuse HIF detection systems, were simulated, such as capacitor switching, transformer inrush current, nonlinear loads, and power-electronics sources. A new set of criteria for fault detection is proposed. Using these criteria, the proposed method is evaluated and its performance is compared with the existing methods. These criteria are accuracy, dependability, security, safety, sensibility, cost, objectivity, completeness, and speed. The proposed method is compared with the existing methods, and it is shown to be more reliable and efficient than its existing counterparts. The effect of choice of the pattern classifier on method efficacy is also investigated.
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