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A single-unit thermal converter for precision ac current measurement is desirable because of its relatively small package and low power dissipation. In this article, high-current multijunction thermal converters (HC-MJTCs) on silicon (Si) substrates fabricated by wet chemical etching have been investigated at input rms currents of up to 2 A. The use of wet chemical etching aids the fabrication of a freestanding nitride–oxide membrane, maintaining the Si heat reservoir under the heater of the HC-MJTC intact. Below 10 mPa, the output voltage from the HC-MJTC and the thermal time-constant increase by approximately six times, implying improved efficiency of the thermal current converter. The absolute value of the ac–dc differences of the device was less than $17~\mu \text{A}$ /A over input current levels of up to 2 A at frequencies above 100 Hz. However, input current level-dependent ac–dc differences were observed at frequencies below 400 Hz even under vacuum. This behavior originated primarily from a change in the electrical resistance of the heater in this Si-based device. Therefore, these low-frequency ac–dc differences can be substantially compensated using the measured ac and dc electrical resistances of the heater. [ABSTRACT FROM AUTHOR]

Cu–Al composite plate corrosion tests, under a 0–100 A AC current, were conducted for 48 hr in a neutral salt spray. The morphology and corrosion products were studied by scanning electron microscope and X‐ray powder diffraction, through which the effect of the current was analyzed. Meanwhile, the rate and degree of corrosion were evaluated by weight loss, electrochemical and electrolytic conductivity detection methods. The results showed that when the current increased, the corrosion rate initially increased and then decreased. When the current value was 50 A, the corrosion rate was the highest. The corrosion of the Cu–Al composite plate mainly included galvanic corrosion at the interface and pitting on the aluminum matrix, with no corrosion on the copper matrix. The state of the passivation film changed to loose, peeling, rupture, accumulation, compact, and so on when the current value increased. The type of corrosion product was not affected by the current value. The current affects the electromobility of the chloride ions by influencing the conductivity of the corrosion medium. The higher the electromobility of the chloride ions, the less the destruction of the passivation film and as a result, there is a decreased rate and degree of corrosion. [ABSTRACT FROM AUTHOR]

This letter presents an approach to develop an exact, unified model of zero voltage switching (ZVS) regions and ac-port currents (peak and RMS) in dual active bridge type dc–dc converters for all its operating modes and modulation strategies. It is executed for a single-phase system, where the method is used to compute closed-form expressions of ac current at switching instants. Then, exact formulae of ZVS regions for all devices, system peak, and RMS currents are derived. Simulation and hardware results for forward and reverse power transfer are reported to validate the proposed approach. [ABSTRACT FROM AUTHOR]

This paper describes the influence of magnetization of an instrument current transformer (ICT) core on ICT errors, and presents a procedure for demagnetizing an ICT. The dependence of ICT errors on the magnetization of the ICT core for different magnetic materials is given in the paper, together with a detailed procedure for ICT demagnetization. The results of experiments are summarized, and conclusions are drawn on when ICT demagnetization is necessary, and on how to prevent the destruction of an ICT due to its winding being punctured. [ABSTRACT FROM AUTHOR]

The frequency and temperature dependences of the ac electrical conductivity of the MnGaInSe4 single crystals have been investigated. It has been established that, in the temperature range of 295.5–360 K at frequencies of 2 × 104–106 Hz, the electrical conductivity obeys the regularity σ ~ fS(0.1 ≤ S ≤ 1.0). It is shown that the frequency dependence of the electrical conductivity for the MnGaInSe4 single crystal can be explained using a multiplet model and the conductivity in these single crystals is implemented via the band-hopping mechanism. The activation energies have been determined on the basis of dependences logσ ~ 103/T. [ABSTRACT FROM AUTHOR]

A novel high-precision wattmeter is developed based on a standard watt converter design using time-division multiplication. A commercial 22-b delta–sigma A/D converter is used for the measurement of the watt converter output dc voltage. The measurement results are presented on a local display. In addition to power, the instrument measures ac voltage and ac current and displays their measured values on separate displays. Two prototypes were tested and compared with an existing standard watt converter connected to a high-precision digital voltmeter. The measurement results are presented and analyzed. Achieved measurement uncertainties (k = 2) of the power measurement are better than 50 μW/VA. [ABSTRACT FROM AUTHOR]

Multijunction thermal converters (MJTCs) are in routine use at the National Institute of Standards and Technology for ac voltage measurements at levels from 250 mV to 60 V, over the frequency range from 10 Hz to 100 MHz. The use of these devices has resulted in reductions in uncertainty of as much as 60% at some points in the voltage parameter space. A new generation of MJTCs, optimized for ac current metrology, promises to accomplish much the same results over the parameter space for ac current transfer difference. This paper describes the motivation for this project, the new designs under consideration, and the results of the work. [ABSTRACT FROM AUTHOR]

A single pancake coil without turn-to-turn insulation was tested in this paper to investigate the transient responses under different situations. We performed charging and discharging test, AC current test, and regional quench emulation test on the non-insulated (NI) coil. The experimental test results show a significant time delay for charging and discharging characteristics of NI coil and can be validated by a simple proposed equivalent electrical circuit. Under the AC operating current, the NI coil can bypass nearly all the AC current from the coil spiral path to the radial path such that it is not possible for NI coil to store or be affected by the AC magnet field. Additionally, while carrying AC current, the AC loss dissipation of NI coil is inversely proportional to the frequency of the AC operating current. When a regional quench occurs, the NI coil can bypass the current in the regional quench zone to avoid further temperature accumulated and protect the NI coil itself. [ABSTRACT FROM AUTHOR]

• Mobilization of metals was deeply assessed by exhaustive sampling of soil and water. • AC current was more effective in mobilizing metals despite not causing electroosmosis. • Accumulation of metals in ryegrass tissues was significantly increased between 17 and 41%. • BCR extraction showed that electric current increased Pb and Cu availability in tailings. Electrokinetic-assisted phytoextraction (EKPH) involves the use of electric current to improve the mobilization of metals in soils and, therefore, their removal efficiency. It emerges as an interesting sustainable technology for the rehabilitation of abandoned mining areas. The goal of this research was to conduct a comprehensive study of this technique applied to real mine tailings from an abandoned Pb/Zn mine by using ryegrass as plant species and two types of electric current: direct with polarity reversal (DC-PR) and alternate (AC). The EKPH tests were conducted in specially designed plastic containers that allowed recording the main parameters of the electrokinetic process and sampling the different matrices studied, i.e. water, soil and plants. This intensive sampling program allowed detailed monitoring of the metal mobilization processes for the different treatments applied. The changes caused in metal mobility and physicochemical parameters of the tailings due to the application of electric current were reflected to a greater extent in the water samples than in solid ones. Accumulation of Pb, Zn, Cd and Cu in ryegrass tissues increased significantly by 41%, 17%, 34% and 32% when applying 1 V cm−1 of AC current, with respect to the results of phytoextraction without electric current. The application of DC-PR current did not lead, in general, to statistically significant increases in the plant metal uptake. These findings were adequately correlated with the changes found in the metal concentrations of soil pore water and, to a lesser extent, with those observed from the BCR sequential extraction applied to tailings samples. [Display omitted] [ABSTRACT FROM AUTHOR]

The morphological, structural and optical characterizations of Al/Al 2 O 3 /Ni-Fe cermet solar absorbers have been investigated. The X-ray diffraction patterns indicated the presence of Ni-Fe alloys with variable composition. However, the formation of Ni-Fe amorphous phases was detected for compositions as high as 73% of Fe. X-ray photoelectron spectroscopy measurements revealed the presence of superficial binary and ternary oxides such as NiO, Fe 2 O 3 , and NiFe 2 O 4 . Furthermore, the properties of solar absorptance and thermal emittance were calculated for the cermets. It was found that the presence of Fe decreased the solar absorptance of the cermets up to 5% and decreased the emittance up to 10%. However, an excessive content of Fe increases the emittance ∼5%. Finally, it was demonstrated that cermets containing Ni-Fe alloys can be useful to enhance the optical and spectral selectivity properties of solar absorbers. [ABSTRACT FROM AUTHOR]

The visible (VIS) and near-infrared (NIR) lasers are now widely used in therapeutic and other medical applications. Some of these applications require to deliver the laser energy deep toward the desired tissue target or organ. The aim of this in vitro study is to investigate practically whether the modulation of laser energy by employing the therapeutic ultrasound or electrical energies can increase the penetration depth of the laser light inside the tissue. Such modulation was implemented in this study by coupling the (c.w.) diode and Nd:YAG laser energies with the ultrasound or AC current simultaneously as they pass through preprepared ex vivo bovine muscular tissue strips. Two wavelengths of diode lasers were used, 637 and 808 nm beside the 1064-nm Nd:YAG laser. The results showed a noticeable decrease of these laser attenuation factors as they pass through the tissue strips in the presence of the ultrasound or AC energies. By using this coupling modulation, the capability of increasing the laser penetration depths inside the tissue was confirmed without having to increase their applied power. [ABSTRACT FROM AUTHOR]

A paralleled multilevel inverter topology consists of n three-phase three-level current-fed inverters (CFIs) connected in parallel on ac side. AC currents with (2n+1) levels can be generated utilizing redundant switching states when all three-level inverters have equal dc-link currents. However, the multilevel space vector diagram gets modified, redundancy in the switching states is lost and the multilevel current pattern changes when the dc-link current of all inverters is not the same. This introduces low-frequency harmonics in output current, thereby deteriorating total harmonic distortion (THD). The presence of low-frequency components in the output current could be avoided by selecting suitable switching state vectors and ensuring proper time sharing among these vectors. Two methods to select such switching state vectors are proposed in this paper. In the first method, a reference current space vector is realized using the nearest switching state vectors. However, this method results in low-frequency pulsation in dc-link voltage of each inverter. In the second method, the switching state vectors are chosen to eliminate this low-frequency pulsation. Effectiveness of these methods is experimentally validated for a five-level CFI. Further, performance of these methods is compared based on efficiency, THD, and dc-link voltage ripple for various inequality ratios in dc-link currents. [ABSTRACT FROM AUTHOR]

A highly precise and accurate system comprising several ac shunts and an inductive voltage divider (IVD) is proposed for characterizing high-accuracy, wideband transconductance amplifiers (TCAs). Frequency characterization of the shunts and the IVD confirms the wideband (up to 100 kHz) performance of the proposed system. Evaluation of two TCAs up to 100 kHz with the proposed system reveals frequency-, current-, and load-dependent properties as well as phase shifts between the input voltage and the output current. The results for the load dependence show that the load differences have a limited impact on the phase shifts up to 10 kHz. [ABSTRACT FROM PUBLISHER]

Current carrying capabilities of HTS tapes and coils can be defined by critical current when carrying DC current. While there is no standard criterion to judge their AC current carrying capability. In actual industrial applications, HTS tapes and coils often need to work in AC conditions. Accurately calculating the current carrying ability of tapes and coils is a precondition of designing a HTS machine. DC and AC V-I properties are measured using four-probe method under different background magnetic field. The method of measuring and obtaining the AC maximum working current is given. The applicability of the method and phenomenon of experiment is discussed based on the Anderson-Kim flux creep model. The content of this paper moderately contributes to the completion of superconducting technology. And the paper can be referenced when designing HTS machine with HTS tapes or coils carrying AC current. [ABSTRACT FROM PUBLISHER]

The bonding of electrical equipment plays a crucial role in maintaining the same potential between conductive parts likely to be energized and conductive parts liable to introduce a “zero” potential into the premises. Voltage rises between such parts are unsafe, as they may induce harmful currents through the human body, the magnitude of which may vary depending on a number of factors. This paper seeks to clarify the bonding requirements in low-voltage electrical systems, by using the concepts of exposed conductive parts and extraneous conductive parts, present in the International Electrotechnical Commission standards, applied to a proposed electric shock model of the human being. With the purpose of reducing the consequences of electric contacts, the authors propose objective criteria to decide whether conductive “dead” objects and enclosures of electrical equipment must be bonded or not. [ABSTRACT FROM PUBLISHER]

An accurate direct measurement of ac current that avoids complex and time-consuming ac-dc current transfer measurements by directly measuring the ac voltage drop of coaxial current shunts is described. Evaluation of custom-developed coaxial current shunts for long-term drift, self-heating effects, and loading using a commercial ac voltmeter is presented. By correcting only the shunts' long-term drift, direct ac current measurement uncertainties below 55 μA/A are attained in the frequency range of 20 Hz-30 kHz and for currents ranging from 100 mA up to 10 A. [ABSTRACT FROM AUTHOR]

The article focuses on the heat transfer mechanisms involved in the electric arc furnaces (EAF) with different gas atmospheres. It states that electric arc furnace steelmaking started from a melting and refining unit to become a highly intensive melting unit. The heat amount supplied to the EAF affects the melting rate and power delivery in EAF is influenced also by thermal properties on the gases. Moreover, the role of applying the Channel Arc Model (CAM) on the power delivery is presented.

The computer numerical control (CNC) machine has recently taken a fundamental role in the manufacturing industry, which is essential for the economic development of many countries. Current high quality production standards, along with the requirement for maximum economic benefits, demand the use of tool condition monitoring (TCM) systems able to monitor and diagnose cutting tool wear. Current TCM methodologies mainly rely on vibration signals, cutting force signals, and acoustic emission (AE) signals, which have the common drawback of requiring the installation of sensors near the working area, a factor that limits their application in practical terms. Moreover, as machining processes require the optimal tuning of cutting parameters, novel methodologies must be able to perform the diagnosis under a variety of cutting parameters. This paper proposes a novel non-invasive method capable of automatically diagnosing cutting tool wear in CNC machines under the variation of cutting speed and feed rate cutting parameters. The proposal relies on the sensor information fusion of spindle-motor stray flux and current signals by means of statistical and non-statistical time-domain parameters, which are then reduced by means of a linear discriminant analysis (LDA); a feed-forward neural network is then used to automatically classify the level of wear on the cutting tool. The proposal is validated with a Fanuc Oi mate Computer Numeric Control (CNC) turning machine for three different cutting tool wear levels and different cutting speed and feed rate values. [ABSTRACT FROM AUTHOR]

A new type of AC current shunt for AC-DC current transfer is presented for which the AC-DC current differences at frequencies from 10 to 100 kHz are calculated with uncertainties smaller than plusmn 9 muA/A in the current range of 30 mA-10 A. This is an independent realization of the AC-DC current-transfer standards in addition to the step-up method used at most National Metrology Institutes. The construction, modeling, and experimental verification of the shunts are described. [ABSTRACT FROM PUBLISHER]

In this study, a prototype HTS cable conductor with 1 layer of 10 Bi-2223/Ag tapes was fabricated and the quench development due to the influence of external magnetic fields was investigated. Firstly, AC current whose peak value amounts around two times critical current was applied to the HTS cable conductor. From the experiments, the influence of self field was considered to be small enough not to affect the transporting characteristics. Secondly, external magnetic fields of 50 and 100 mT were applied to the HTS cable conductor transporting AC current. In this case, due to the directional dependence of Bi-2223/Ag tapes on magnetic field, various magnitudes of voltages were detected in each strand. Finally, the quench development with the magnitude of the applied external magnetic field was analyzed. [ABSTRACT FROM AUTHOR]

A case of inappropriate detection of an ungrounded external AC current by an implantable cardioverter defibrillator (ICD) is reported. The resultant ICD shock dislodged the patient from the electrical source, thus preventing injury or electrocution. [ABSTRACT FROM AUTHOR]