Alternating Current Direct Current Research Articles

PSCAD based multi-infeed HVDC system simulation validated by a recorded fault

More and more high voltage direct current (HVDC) converters are being located in a load area in the Yangtze River Delta Region in China. It’s large transmission capacity and intensive placement are hardly seen in other countries. Accurate and reliable study tools and methods are extremely needed for power system engineers and researchers to deal with such problems which were never met before and otherwhere. A novel approach on electromagnetic modeling of alternating current / direct current (AC/DC) system is proposed and simulation is carried out to replay a real AC 3-phase to ground fault on a multi-infeed high voltage direct current (MIHVDC) system. AC system is specially simplified. Dynamic models and real parameters are adopted in main AC/DC equipments concerned and retained. Modeling and simulation are based on the power system computer aided design/electro-magnetic transient in direct current (PSCAD/EMTDC) system software package. Comparisons between simulation results and the records from the fault recorders are studied including both AC and DC quantities.

A comparison of electrofishing methods and fyke netting to produce reliable abundance and size metrics

Because different fishing gears may introduce different degrees of bias, we set out to compare two active sampling methods (alternating current (AC) and pulsed direct current (DC) boat electrofishing) and one passive method (modified fyke netting) in sampling sportfish in a midwestern US reservoir. Currently, the Illinois Department of Natural Resources uses AC electrofishing to sample reservoirs but a switch to DC is underway. Understanding how this switch will impact fisheries data is critical for future management decisions. We found catch per unit effort (CPUE) for all sportfish combined was greater (p < 0.0001) with AC electrofishing than DC electrofishing. Though not significant, largemouth bass (Micropterus salmoides) were sampled at a higher rate using DC electrofishing. Channel catfish (Ictalurus punctatus, p = 0.0494) and sunfish (Lepomis spp., p < 0.0001) were sampled at a significantly higher rate with AC electrofishing. We found a positive relationship between AC and DC electrofishing CPUE for largemouth bass (r 2 = 0.702); however, no relationship between AC electrofishing and DC electrofishing was found for sunfish CPUE. Length frequency distributions of sunfish were significantly different for each gear used. The lack of a relationship between AC and DC electrofishing CPUE for sunfish species suggests data from future DC electrofishing may not be comparable to historical data obtained from AC electrofishing.

Three-wire network: a new distribution system approach considering both distributed generation and load requirements

SUMMARY This paper proposes a new approach to distribution system named Three-wire Network (3-NET). Considering the integration of different distributed generation (DG) technologies as well as the diversity of loads, the idea of 3-NET is splitting a single power network into three qualitatively different networks: (i) a high quality direct current (DC) network; (ii) a conventional alternating current (AC) network; and (iii) a low quality DC network. By this configuration, the multi-stage conversion of energy from DG sources can be reduced, whereas loads can be supplied with different power quality and reliability levels as desired. In order to evaluate the potential benefits of 3-NET, the operational strategy is formulated in a market model; the reliability performance is investigated using Monte Carlo simulation and quantified in terms of interruption costs. In the case study, the proposed 3-NET is considered for integrating a certain amount of DG into a specific distribution system and then compared with another system approach: hybrid AC–DC microgrid. The simulation shows that although the operation costs can be slightly higher, the 3-NET shows a great improvement in reliability performance in comparison with the hybrid microgrid. Copyright © 2013 John Wiley & Sons, Ltd.

Electrical waterbath stunning: Influence of different waveform and voltage settings on the induction of unconsciousness and death in male and female broiler chickens

Stunning effectiveness of male and female broiler chickens was analyzed in response to different waveforms at 3 constant voltage levels. In total, 180 male and female broiler chickens were stunned using a sine wave alternating current (AC) of 50 Hz, rectangular AC of 70 Hz, and pulsed direct current (DC) of 70 Hz (duty-cycle 1:1) with a constant voltage of 60, 80, or 120 V, respectively. In each stunning group, 10 male and 10 female birds were stunned for 4 s. The current obtained by every bird was recorded. For stunning efficiency, the electroencephalogram (EEG) and physical reflexes were recorded and analyzed. The EEG was recorded for 120 s poststun. Simultaneously, the occurrence of spontaneous eye blinking, wing flapping, and breathing was assessed, and the corneal reflex was tested every 20 s poststun. The EEG was analyzed regarding the occurrence of a profound suppression to less than 10% of the prestun level in the 2 to 30 Hz and 13 to 30 Hz bands. Female broilers obtained a significantly lower stunning current compared with that of the males. This resulted in a lower stunning efficiency for females, when the same constant voltage was applied to males and females. The waveforms required different amounts of currents to achieve a 90% stunning efficiency. A minimum necessary stunning current of 70, 90, and 130 mA could be established for sine wave AC, rectangular AC, and pulsed DC, respectively. The low stunning efficiency of pulsed DC might be caused by the short stunning time of 4 s. This effect should be further investigated for DC stunning. Very few birds stunned with AC resumed breathing following stunning, indicating stun to kill. Pulsed DC stunning showed a lower effect on the induction of death. The level of wing flapping, indicating convulsions and possible meat quality defects, was higher for the AC treatments.

Modified alternating current defibrillation: a new defibrillation technique

Defibrillation is the only clinically effective treatment for ventricular fibrillation (VF). Early defibrillation improves the outcome and increases the chance of survival with full recovery. Immediate availability of a home-based defibrillator using mains-derived alternating current (AC) current will drastically improve the outcome. The aim was to develop a defibrillator based on the modulated AC, resembling biphasic configuration, and compare its efficacy, in a pig model, with a standard direct current (DC) defibrillator. A computer controlled, modulated AC defibrillation system was developed using a high-voltage switch and a high-voltage transformer. The efficacy and safety was evaluated in five pigs (30-40 kg), under general anaesthesia with ketamine and isoflouran. A single quadripolar-pacing catheter was inserted percutaneously. Ventricular fibrillation was induced with rapid ventricular burst pacing, and stable VF was defibrillated after 15 s. Defibrillation threshold (DFT) was determined in each animal with AC and standard DC shock using the step-down protocol. A biphasic-like shock was used with a short isoelectric stage between the phases. The DFT with AC was 70.83 +/- 24.81 J and with DC was 65.83 +/- 12.41 J (P = 0.49). No macroscopic damage was observed after AC or DC defibrillation. Modulated AC defibrillation is safe and effective as the commercially available DC defibrillation. The defibrillator is built from an inexpensive high-voltage transformer, without the need for capacitor, batteries, or routine maintenance, delivers repeated shock without any delay, and provides pacing as well. It may be an ideal platform for automatic home defibrillator.

Electroremediation of Naphthalene in Aqueous Solution Using Alternating and Direct Currents

The key objectives of this study were to evaluate the use of an alternating current (AC) for the degradation of naphthalene in spiked aqueous solutions and to investigate the effect of current density on the degradation rates of naphthalene. Direct current (DC) was also used to compare the rates of degradation. Sodium chloride (NaCl) and anhydrous sodium sulfate (Na2SO4) were used as the supporting electrolytes. Degradation rates and byproducts formed were investigated when DC and AC were separately passed through naphthalene solutions. A square wave AC, having a frequency equal to 0.1Hz was used. Naphthalene solutions having an initial concentration of about 20mg∕L(∼0.15mM) were subjected to an AC peak current density and DC density of 6mA∕cm2, using NaCl as the supporting electrolyte. An approximate 65% reduction in the concentration of naphthalene was observed after a period of 48 h when DC was applied. Degradation was almost 100% when the AC was applied during the 48-h period. The effect of current density on the electrochemical degradation rate of naphthalene in aqueous solution was also investigated at alternating and direct current densities of 1, 3, and 6mA∕cm2 using Na2SO4 as the supporting electrolyte. AC peak current densities of 1, 3, and 6mA∕cm2 resulted in overall conversions of 77, 87, and 95%, respectively, of naphthalene in solution. The corresponding values for DC application were 95% for all current densities while the initial degradation rates were greater at higher DC densities. Based on the degradation products formed, hydroxylation is believed to be the key mechanism for the degradation of naphthalene.

Electroless nickel–phosphorus coatings to protect steel reinforcement bars from chloride induced corrosion

Electroless nickel–phosphorus (ENP) alloy coatings deposited on steel surfaces provide a high degree of protection against corrosion in comparison to the bare steel exposed in chloride-contaminated simulated concrete pore solution (SPS). Electrochemical AC (alternating current) impedance spectroscopy (EIS) and DC (direct current) polarization techniques, scanning electron microscopy (SEM) and X-ray diffraction (XRD) studies have been used to study the kinetics and mechanism of corrosion protection and to characterize corrosion products. The pH of the deposition solution of coating plays very significant role on corrosion resistance of the deposited coatings. It is observed that ENP deposited at pH of 4.00 attains a very slow rate of corrosion from very beginning of their exposure in the test electrolyte, indicating that surface of the coating attains passivity in the solution. The coatings deposited at higher pH, however, show an increasing rate of corrosion with time. Medium phosphorus content (about 8%) coating is more impervious and protective in comparison to high phosphorus coating (16%). The heat treatment of deposited coatings has deleterious effect on their corrosion resistance. X-ray diffraction studies show that the medium phosphorus electroless nickel (MEPEN) is microcrystalline in nature and forms Ni 2O 3 and Ni 5P 2 passive films on its surface.

An airborne intensive care facility (fixed wing).

A fixed-wing aircraft (Beechcraft KingAir B200 C) fitted as an airborne intensive care facility is described. It completed 2000 missions from 1987-1992 for distances up to 1300 km. Features include: 1. Space for carriage of two stretchers, medical cabin crew of up to five persons and equipment and two-pilot operation if necessary. A third stretcher may be carried in emergencies. 2. Two CARDIOCAP (TM) fixed monitors for ECG, invasive and noninvasive pressures pulse oximetry and end-tidal C02 plus SIEMENS 630(TM)/PROPAQ(TM) compact monitors for the ground transport phase of missions, or the total duration. 3. A medical oxygen reservoir of 4650 litres sufficient for two patients on IPPV with FiO2 = 1.0 for a four-hour trip. The medical suction system is powered from the engine or a vacuum pump. 4. Other medical equipment and drugs in portable packs, for ground transport and resuscitation needs and for replenishment by nursing staff at the parent hospitals. 5. Stretchers compatible with helicopter and road ambulance vehicles used. 6. A stretcher loading device energized from the aircraft, operating through a wide (cargo) door. 7. Provision of 24Ov AC (alternating current) and 28v DC (direct current) electrical energy. 8. Pressurization and climate control. 9. Satisfactory aviation performance for conditions encountered, with single-pilot operation.

Mass transfer in AC electrolysis part II: Experimental study on sinusoidal current

AbstractAn experimental study has been made for laminar mass transfer to a rotating disk and a rotating hemispherical electrode when sinusoidal alternating current (AC) together with direct current (DC) are flowing across the electrode/electrolyte interface. A resistor‐capacitor circuit was used to measure the phase shift between the applied AC and the resulting periodical concentration overpotential. The limiting AC current density corresponding to a zero instantaneous surface concentration was determined as a function of AC frequency and DC current density. The experimental data agreed with the theoretical calculations in a regime of a dimensionless AC frequency K = (ω/Ω)Sc1/3 greater than 1 and less than 200.