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Litz wire has been widely utilized in power transformers and inductors as a wire with low copper loss at high-frequency operation. The Litz wire is commonly made of many thin isolated strands twisted in multiple levels. Due to its complicated structure, the copper loss prediction of the Litz wire has been difficult, hindering the design optimization of the Litz wire structure. To overcome this difficulty, preceding studies have investigated the analytical copper loss models of the constituting elements of the Litz wire, i.e., the strands and the bundles of strands. The purpose of this article is to propose an analytical copper loss model of the Litz wire by utilizing these preceding knowledge. The proposed model is formulated only with parameters that can be measured by basic testing instruments. Besides, the proposed model considers the bundle structure of the Litz wire, which affects the local ac current distribution, and the twisting pitch, which causes the inclination of the Litz wire strands. The proposed model was tested by comparing the analytical prediction and experimental measurements of the ac resistance of commercially available Litz wires. As a result, the predicted ac resistance showed good agreement with the measured ac resistance, suggesting the appropriateness of the proposed model.

Effects of elastic stress and alternating current (AC) on corrosion behavior of X80 pipeline steel were investigated in a simulated soil solution by electrochemical techniques and surface analysis. Corrosion current density was 40.5 μA/cm2 by synergistic effects of the stress and the AC current, being about five times of that without the stress and the AC current. Corrosion morphology of the steel coupon was pitting corrosion with application of AC current, and changed from pitting corrosion to moat corrosion under effects of the stress and the AC current. Corrosion of the steel coupon was enhanced by increasing anodic dissolution of iron and porosity of corrosion product film.

Compared to conventional transformers, high temperature superconducting (HTS) transformers have higher efficiency and fewer hazards, whose main loss comes from the ac loss of high temperature superconducting windings carrying ac current. Their radial leakage magnetic fields are perpendicular of HTS winding tapes, which is the main parameter affecting the ac loss. In the study of superconducting magnets, the flux diverter has been used to reduce the radial leakage magnetic field. The effect of the flux diverter installed at the top of the transformer windings on the coil ac loss was explored in this paper. The influence of different structure, slotting, and the number of slots on the transformer was also discussed, which laid a theoretical foundation for the optimization of flux diverter on the 6.6 MVA HTS transformers. Besides, in this paper, we choose the homogenization treatment method to reduce the computing time and memory when modeling.

The windings of high-frequency high-current transformers are required to reduce the proximity effect loss. Therefore, the Litz wire in parallel connection of interleaved winding layers is usually used as the winding of transformers. However, this can cause unbalanced AC current distribution, hindering effective reduction of the copper loss. This paper solves this problem by optimizing the distance between the winding layers based on the analytical principle called the extremum co-energy principle. The transformers used in the experiment to verify this method consists of three parallel-connected primary winding and two parallel-connected secondary winding, PQ core, thin polypropylene sheets for adjusting the distance between the winding layers. As a result, the copper loss can be recused by homogenizing the AC current distribution, and the effectiveness of this method has been clarified by experiments.

Widespread adoption of electric vehicles (EVs) requires additional safety countermeasures to prevent DC injection from EVs into the AC grid via Electric Vehicle Supply Equipment (EVSE). Moreover, for energy purchase, and even more so for vehicle-to-grid (V2G) services, the EVSE must conduct high precision bidirectional power and energy measurements. This paper introduces operating principles, structure, performance, and cost comparison of three current sensing technologies&mdash, current transformer, shunt and fluxgate&mdash, for metering and protection within an EVSE, concluding with recommendations among those sensors for the most beneficial applications concerning EV charging.

This paper describes the development of an active current shunt. The device is intended for measurement of current with in the nA- and $\mu \mathrm{A}$ -range and high frequency up to 1 MHz with negligible impact on the circuit. An introduction of the developed active shunt into the current path does not result in distortion of signals of the test circuit. This makes the active shunt suitable for low current in-circuit measurement.

Battery impedance measuring techniques provide accurate estimation of electrochemical parameters. This paper presents an AC current injection circuit, which is connected to the Li-ion battery in parallel with an LC filter-based dc/ac inverter configuration. The proposed approach injects AC perturbation current into the battery in order to measure internal battery impedance without a battery charger. It performs an AC sweep, and the measured voltage, current, and time data are processed to estimate battery impedance. This data will be utilized for further analysis for preventive maintenance and safety precautions in the battery management system. The performance of the proposed current injection and measurement technique is validated using simulations through PSIM and MATLAB Simulink and was tested with a 40Ah 13.6V Li-Ion battery.

This talk is related to chemical application of carbon nanotubes (CNT). The talk describes DC influence on a few CNT coatings, therefore research also involves investigation of electric field influence on different CNT solutions, in particular, solutions based on functionalized CNT. As a side effect of AC current influence on CNT solution nanostructurized composite was obtained. These results can be used in chemical industry, for example, in chemistry of polymers.

The modular multilevel converter-based unified power flow controller (MMC-UPFC) is able to operate under unbalanced grid conditions with symmetric component decoupling. However, the constraint of the voltage limit of UPFC is not considered and no protection schemes are investigated to protect the UPFC from overmodulation under unbalanced grid conditions. To solve this problem, this paper proposes the cascaded control scheme for MMC-UPFC based on voltage limit control and symmetric component decoupling to balance the ac current of the transmission line. With appropriate transformer connections for MMC-UPFC, the negative- and zero-sequence currents are suppressed by the corresponding inner current loops. Considering the voltage limit of MMC, the operating ranges of UPFC-MMC under balanced and unbalanced grid conditions are investigated in both mathematical derivation and point scanning methods. The results are depicted and analyzed in 3-D vision. Based on the analysis of operating regions, the voltage limit control is proposed to protect the MMC from overmodulation and to maximize the controllable region under unbalanced grid conditions. Finally, the final cascaded control structure is constructed. The simulation results obtained in PSCAD/EMTDC are provided to validate the effectiveness and robust performance of the proposed control strategies.

This study presents a modified proportional-resonant (M-PR) control topology for single-stage photovoltaic (PV) system, operating both in grid-connected and stand-alone modes. Dual two-level voltage source inverter fed three-phase open-end winding transformer is used to supply the load in this scheme. The M-PR controller is developed for the inner current control loop of the system. The M-PR controller has the ability to track ac current with zero steady-state error. The outer dc-link voltage control loop is developed through the indirect vector control method at synchronously rotating reference frame. The control scheme ensures improved performance of the system at variable solar irradiance and load disturbances. The performance analysis of the dual two-level PV inverter is carried out for different operating conditions. The control scheme is implemented in MATLAB-SIMULINK environment. The theoretical results are verified through experiments in a laboratory prototype. The experimental results show close match with their theoretical counterparts.

DC-link current is an important parameter for selection and design of DC-link capacitor or battery. Considering the AC current ripple, this study introduced a general DC-link current real-time prediction method for three-phase two-level voltage inverters (three-phase 2L-VSI) using the pulse width modulation. Compared with the traditional analysis which just takes AC average current into consideration, the time-domain comparison and spectral analysis of DC-link current have been studied. Meanwhile, accurate calculation of RMS current on the DC-link capacitor has been provided. Simulation results and experimental results are provided to support the analysis and proposed method.

Purpose With the rapid development of rail transportation and energy-delivery systems, such as buried oil and gas pipelines and high-voltage transmission lines, the alternating current (AC) corrosion of buried steel pipelines is becoming more serious. This paper aims to study the corrosion behaviours of Q235 buried steel pipelines induced by the alternating stray current, with a set of indoor simulated experiment apparatuses. Design/methodology/approach The corrosion of the coating holidays of the buried steel pipelines at various AC current densities from 0 to 200 A/m2 in the soil-simulating environment was revealed by the electrochemical and weight-loss methods. Findings The results showed that the corrosion potential of the steel shifted negatively obviously and the corrosion rate of the steel increased with the increasing of AC current density. At a low AC current density, the negative deviation of the corrosion potential of the steel was small and the increase of corrosion rate was slight. However, the negative deviation of the corrosion potential was remarkable and the corrosion rate was greatly increased at a relative higher AC current density. The geometrical shape of the corrosion images indicated the corrosion forms changed from uniform corrosion to local corrosion due to the increase of AC interference. Originality/value Investigation results are of benefit to provide a new strategy to forecast and evaluate the AC-induced corrosion of the buried pipelines which could improve the safety of pipeline transportation.

Many buried oil and gas pipelines are parallel to the high-voltage transmission lines and electrified railways in a long distance. Alternating current (AC) corrosion of these pipelines are very significant in such cases, and might lead to leakage even serious accidents. Laboratory experiment was carried out through weight-loss method in a simulated soil solution at various AC densities from 0 to 200 A/m2 and frequencies from 10 to 200 Hz. The results indicated that the corrosion rate increased with the increasing of AC current density. Furthermore, with the increase of AC interference frequency, the AC current involved in the electrode reaction process is decrescent, which caused a lower corrosion rate of pipeline steel. Morphology and corrosion product investigations explained that a better anti-corrosion behavior of X80 than that for X60 and X70 under AC interference. The investigation results are benefit to provide a new strategy to forecast and evaluate of the AC-induced corrosion, and design of the buried X series oil/gas pipelines.

This paper introduces the design and some experimental results of a high power-density integrated inverter prototype based on full-SiC devices. The inverter prototype is a 2-level voltage source inverter, and the whole system is cooled by force air. In this inverter prototype, we integrated a DC voltage sensor and three AC current sensors with the main circuit. We applied thin-film capacitors paralleled to decrease stray inductance of main circuit to nearly 10nH. The volume of the prototype system is about 9.3dm3 and the weight is about 36.25kg. Experimental performance shows that the rated output power of the prototype inverter can up to 132kW, which is larger than the conventional IGBT inverter by 18.2%. In this case, the power density of the proposed inverter is 14.19kW/dm3 or 3.64kW/kg and the efficiency of which can up to 98%.

AC corrosion has been considere d as a threat to the corrosion of buried pipelines. Effects of sulfate-reducing bacteria (SRB) and alternating current (AC) on corrosion of X80 pipeline steel in soil-extract solution were investigated by electrochemical and surface analysis techniques. AC current can inhibit the growth of planktonic and sessile SRB. The corrosion current density of steel with 10 mA/cm2 AC current is about nine times bigger than that without AC current. Corrosion morphology changes from small pitting to large pitting holes with increasing AC current density. Corrosion of steel with SRB and AC current is controlled by both active dissolution of iron and film degradation.

Although high-voltage alternating-current (HVac) and direct-current (HVdc) are the technology of choice for long distance bulk power transmission, low-frequency HVac (LF-HVac) has been recently proposed to combine the strengths of HVac and HVdc approaches. The proposed transmission scheme operates at a low frequency thus requiring power converters to convert ac current to and from the standard HVac power frequency. The objective of this paper is to lay out fundamental requirements of power converters for LF-HVac applications. Suitability of common inverter topologies such as cycloconverters, matrix converters, and back-to-back converters are analyzed and compared. Further, initial simulations of LF-HVac involving back-to-back converters are presented.

This paper proposes a new system for detection of underground tunnels. The proposed system is based on underground installed coil, which is supplied by AC current source. The coil radiates magnetic field in the underground space. This magnetic field is deformed when iron or metal objects are present in the underground space. These distortions are measured by pick up coil and filtered by electronic unit. By identification of distortions the presence of underground metal and iron object are identified. The system was validated by extensive experiments that show that the proposed system successfully identifies underground objects.

A different version of an ac current comparator with voltage sources operated at low frequency (below 13 Hz) and at room temperature has been designed. Two ratio windings of 1600/16 and 2065/16 are built. Preliminary experiments at 2.03 Hz and 13 Hz using given resistance ratios indicate that the comparator ratio errors (extrapolated to 0 Hz) are at the level of $\pmb{10^{-8}}$ . The further improvements of the low frequency current comparator will be implemented, which are expected to extend the frequencv range below 1 Hz.

This paper presents a technique to compare two current transformers, or a current transformer and ac current shunts, with an uncertainty better than 1 uA/A and 1 urad at audio frequencies. Examples of such a comparison at frequencies from 10Hz to 10kHz are given. Due to its low uncertainty, the described technique made it possible to accurately measure critical parameters such as common-mode dependence of a current transformer and impedance variation of current shunts with ac current applied.

Traceability of the current ratio is crucial for the measurement of electrical energy in revenue metering. A comparison of the AC current ratio was therefore performed within EURAMET in the time period 2012 - 2016, using a precision CT as the traveling device. The Czech Metrology Institute (CMI) as coordinator processed the measurement results of the 15 European participating laboratories. The comparison of the results for transformer ratios of (4, 5, 6, 8, 10) kA/5 A at 15 VA burden and (4 and 10) kA/5 A ratios at 5 VA burden indicates good agreement between the participating laboratories. The main differences are found for phase displacement, at least in part due to instability of the traveling standard.

The experimental investigation on the coated pipeline steel was performed with respect to induced stray current including the alternating current (AC), direct current (DC), and the superimposed AC + DC sources in the soil-simulating conditions. The results showed that the corrosion potential and rate increased with the increases of stray current density. The extent of corrosion was found to be less in AC when compared to the DC sources. When an alternating current was superimposed on a direct current, the corrosion rate was larger than their respective corrosion. AC corrosion on the X70 pipeline steel represented three classic patterns, including the uniform corrosion, ring-like corrosion and pitting corrosion according to the geometrical shape of the corrosion images. The corrosion pattern would transfer to the local corrosion from the uniform corrosion, when the AC density increased. The quantity, area and depth of the corrosion pits arose with the increase of the AC current density. The relationship between the pit number or pit area and AC current density followed the power function, y = ai b .

In this paper, we present a MOSFET-based (metal oxide semiconductor field-effect transistor) microfluidic gate to characterize the translocation of red blood cells (RBCs) through a gate. In the microfluidic system, the bias voltage modulated by the particles or biological cells is connected to the gate of MOSFET. The particles or cells can be detected by monitoring the MOSFET drain current instead of DC/AC-gating method across the electronic gate. Polystyrene particles with various standard sizes are utilized to calibrate the proposed device. Furthermore, RBCs from both adults and newborn blood sample are used to characterize the performance of the device in distinguishing the two types of RBCs. As compared to conventional DC/AC current modulation method, the proposed device demonstrates a higher sensitivity and is capable of being a promising platform for bioassay analysis.

Current transformers (CTs) show large errors when they are magnetized by dc current. This error can be reduced after proper demagnetization. One of the methods to demagnetize the CT is to increase the core flux by increasing its burden. The burden should be adjusted according to the measured ac current. In this paper, we show that pulsewidth modulation switchable resistor can be used as variable burden for this application. This method enables to restore the nominal precision of the heavily magnetized CT from 2.5% back to 0.2% without interruption of the CT operation.

In this paper, a generalized switching technique for cascaded H -bridge (CHB) converters is proposed. To take advantage of both low- and high-frequency modulation techniques, a hybrid modulation method is utilized. The proposed technique employs the low-frequency switching for voltage balancing of the dc-link capacitors, and the high-frequency sinusoidal pulse-width modulation switching for shaping the input ac current. Using the proposed technique, the stable operating region of CHB converters is extended. The proposed technique is capable of maintaining the dc voltages balanced even under critical operating conditions in which the load of one H-bridge cell is removed. The validity and effectiveness of the proposed method is confirmed by several simulation and experimental tests on a seven-level CHB rectifier.

Recent experiments on synchronized radiation from intrinsic Josephson junctions in high-temperature superconductors showed that the difference of temperatures of the junctions can influence synchronization. We investigated numerically the mechainsm of this influence on the example of two overdamped Josephson junctions loaded by a shunt consisting of the resistance and the inductance. We showed that strong synchronization of radiation was obtained by means of external separate heating/cooling of junctions. Due to the change of critical currents in the process of heating or cooling, the current–voltage (I–V) characteristics of the junctions cross each other and junctions are synchronized by the ac current in the load in the vicinity of this crossing. The maximal tolerant spread of critical currents for this mechanism of synchronization is 15–20% that is twice larger than the maximal tolerant spread for this system without the separate heating. I–V characteristics of two separately heated junctions. Phase locking in this system is impossible without heating for such large spreads of critical currents.

The real resistor in AC current can be described as an impedance Z of components changed with frequency. The real part R s of this impedance is not equal to the resistance R in the DC current, and there is the imaginary component X s, both frequency dependent. A three-element equivalent circuit including the resistance R as the main parameter and the residual parameters: serial inductance L and a parallel capacitance C is the basic AC model of a real resistor. Frequency characteristics of impedance Z components of this model in relative to R values r s, x s are given. Patterns of these components in generalized form, i.e. as functions of the relative values of characteristic resistance \( \rho = R\sqrt {{C \mathord{\left/ {\vphantom {C L}} \right. \kern-0pt} L}} \) and characteristic frequency \( \eta = \omega \sqrt {C\,L} \) of this equivalent circuit are determined and their frequency curves for a few values of ρ are shown. Variants of this model with four models of connections are analyzed. Relative errors δR, δX and \( \delta Z\mathop = \limits^{{\text{def}}} \sqrt {\delta R^{2} + \delta X^{2} } \) are also find. Few numerical examples are given and considerations are of changes of errors in the frequency band. Some conclusions are included.

A self-designed experiment circuit was adopted to investigate the effect of alternating current (AC) on corrosion rate and cathodic protection (CP) potential of cathodically protected Q235 steel in the simulated soil solution of 4 g/L sodium sulfate. It is found that the corrosion induced by AC current can be controlled by increasing CP current when AC current density is below 300 A/m2. However, in case that CP current is too large the corrosion of Q235 steel will be accelerated. Moreover, CP potential of Q235 steel shifts considerably due to AC current and the shift direction depends on the applied CP current. Based on the experimental results, a combination role of CP current and AC current considering micro-electrons transfer is introduced to explore the mechanism of AC corrosion.

Due to heavy proliferation of power electronic and non-linear loads on a present day utility system, the DC current accumulated at the distribution transformer is significant. DC current shifts the operating point of the magnetization characteristic and hence causes the magnetizing current to exhibit severe asymmetry between positive and negative half cycles in magnitude and shape, owing to magnetic saturation. It affects the shape of input current and recreates a DC current at the input with magnitude even greater. This paper describes the work on influence of DC current on input current in a loaded transformer, and a system to divert DC current completely away from the transformer. Implementation was done with a specially designed current sensor and a fast responsive controlled current source. The later was implemented in power electronic with closed loop control. The work was challenging because measuring of small DC current superimposed with a large AC current was not straightforward, and also injecting a small DC current accurately against a large AC voltage was not straightforward. Both these challenges were successfully overcome and an extremely good DC current diversion system was developed. Details of the design and results of investigations are presented.

A measurement setup is developed for the accurate ratio measurement of ac current transformers (CTs) for primary currents up to 5 kA. A unique property of the system is the use of high-quality digitizers for sampling of the secondary current signals and step-down transformers with different current ratios. This allows for accurate comparison of CTs even when their nominal ratios are not equal. The calibration results of the key components in the setup show that the sampling current ratio bridge has a ratio uncertainty of better than 2 $\mu{\rm A/A}$ in magnitude and 0.8 $\mu{\rm rad}$ in phase for CT-under-test current ratios that do not differ by more than a factor of 5 from one of the ratios in the reference CT. The linearity of the bridge for input currents changing between 1% and 120% of nominal input current is better than 4 $\mu{\rm A/A}$ in magnitude and 0.5 $\mu{\rm rad}$ in phase.

In this work, the effects of alternating current (AC) on the performance of cathodic protection (CP) and the CP potential readings were investigated on a 16Mn pipeline steel in a simulated soil solution. The presence of AC interference decreases the CP effectiveness to protect the steel from corrosion. Only when CP potential is sufficiently negative, the steel is under a complete protection even when the AC current density is 400 A/m 2 . Moreover, the AC would shift CP potential from the designed value. The effect of AC on the CP performance depends on the cathodic potential applied on the steel.

This paper reports on a low frequency piezoelectric energy harvester that scavenges energy from a wire carrying an AC current. The harvester is described, fabricated and characterized. The device consists of a silicon cantilever with integrated piezoelectric capacitor and proof-mass that incorporates a permanent magnet. When brought close to an AC current carrying wire, the magnet couples to the AC magnetic field from a wire, causing the cantilever to vibrate and generate power. The measured average power dissipated across an optimal resistive load was 1.5 μW. This was obtained by exciting the device into mechanical resonance using the electro-magnetic field from the 2 A source current. The measurements also reveal that the device has a nonlinear response that is due to a spring hardening mechanism.

The Dowell model is widely utilized for copper loss analysis of forward transformers. However, this model is not directly applicable to transformers with parallel-connected windings. The reason is that the Dowell model requires determining the AC current of all the windings in advance of analysis, although the AC current distribution in parallel-connected windings is severely affected by disposition of the windings. This issue is addressed in this paper by employing the Dowell model in combination with a novel insight that the AC current is distributed in parallel-connected windings to give an extremum of the magnetic co-energy of the transformer. Simulation and experiment were carried out; and, the results supported appropriateness of the proposed copper loss analysis method.

A high precision wattmeter is devoloped based on a standard watt converter using Time Division Multiplier (TDM). A commercial 22-bit delta-sigma A/D converter is used for the measurement of the watt converter output DC voltage. The measuremnt results are presented on a local display. In addition to power, the instrument also measures AC voltage and AC current and displays their measured values on separate displays. It has four voltage and four current measurement ranges. Achieved measurement uncertainties (k=2) of the power measurement are better than 50 μW/VA.

A variety of diagnostic tests are widely applied in the field in industry to evaluate the condition of high voltage (HV) motor stator insulation. In this paper, the influence of temperature on the stator insulation diagnostic tests such as the insulation resistance, AC current, dissipation factor, and partial discharge measurements are studied and reported. The tests are performed with the HV motor stator winding temperature set between to in intervals. It is shown that the AC current, dissipation factor, and partial discharge magnitude steadily increase with temperature, which suggests that temperature must be taken into account in the interpretation of the test results.

In the present work, the alternating current (AC) induced corrosion of a cathodically protected X65 pipeline steel was studied in a neutral, extracted soil solution and a high pH, carbonate/bicarbonate solution by electrochemical and weight loss measurements, and surface characterisation. It was found that AC corrosion causes the alkalisation of the soil environment in the vicinity of pipeline no matter what the cathodic protection (CP) condition is. The degree of alkalisation depends on the AC current density. In the absence of AC interference or at a low AC current density, i.e. 20 A m−2, a CP potential of −950 mV versus Cu/CuSO4 electrode provides a full protection over the steel. When the AC current density is >20 A m−2, a new CP standard is recommended to avoid AC corrosion of pipelines.Dans le present travail, on a etudie la corrosion induite par le courant alternatif (AC) d’un acier X65 pour pipeline avec protection cathodique, dans une solution neutre d’extrait de sol et dans une solution ...

The Remote Field Eddy Current (RFEC) method is widely used to inspect both ferrous and nonferrous metal tubes when internal access is the only possible way of inspection. An axisymmetric quasi-analytical model is presented in this paper in order to simulate the behavior of a RFEC system during its operation. The proposed model, based on the application of the Fourier Transform in space, is able to take into account the finite length of the excitation coil, fed by an AC current, and the relative movement between the RFEC system and the wall tube. Numerical simulations based on integral formulations and experimental measurements were used to validate the proposed quasi-analytical model.

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 muA/A are attained in the frequency range of 20 Hz-30 kHz and for currents ranging from 100 mA up to 1.0 A.

We measured the field profiles near the surface of a coated conductor (CC) by using the scanning Hall probe method. The external currents, represented by I a , or the external fields, represented by H a , were applied during the measurements. The field was applied in the normal direction with respect to the tape surface. The measured field profiles could be expressed by H ( x , X a ), where the variable, X a , was either I a or H a . The x -axis was parallel to the in-plane transverse direction of the CC tape. The CC tape was fabricated by the IBAD-PLD method. The applied field (current), H a ( I a ), was decreased stepwise from H peak to − H peak (from I peak to − I peak ). From H ( x , X a ), we calculated the current profile, J ( x , X a ), by the iterative inversion method. From J ( x , X a ) and the corresponding flux densities, B ( x , X a ) we calculated the AC current loss, Q C ( I peak ), and the AC magnetic loss, Q M ( H peak ), for various values of I peak and H peak , respectively. The characteristic functions were defined by f C = π Q C / μ 0 I c 2 and f M = π Q M / μ 0 I c 2 , where I c is the critical current. We found that the calculated values of f C ( f M ) were similar to the experimental values of f C ( f M ) which were directly measured for the IBAD-PLD CCs. On the other hand, the values of f C ( f M ) were smaller than (larger than) the values estimated from the experimentally observed Q C ( Q M ) in RABiTS ™ -MOD CCs.

This paper introduces a sensor for detection of DNA hybridization and investigates its performance by means of computer simulation. A planar transformer with spiral windings is proposed for hybridization detection. In order to detect the occurrence of hybridization, single strand target DNA’s are tagged with magnetic beads. Target DNA’s are then exposed to known single strand probe DNA’s which are immobilized on the surface of a functionalized layer in the proximity of the sensor. The primary winding of the transformer is driven by an AC current source. The voltage at the secondary winding is used for detection. Once the hybridization is occurred, a layer of magnetic material is formed and the coupling between the windings is varied. These variations are reflected into the detecting output voltage. The magnitude of the output voltage is numerically calculated in terms of geometrical and physical parameters and the parameter values resulting in maximum response are derived.

Diagnostic, surge and ac breakdown tests are widely used to evaluate the insulation condition of stator winding in traction motor. Diagnostic test included ac current, tan delta and maximum partial discharge. The result of diagnostic test indicates that five kinds of stator windings are good condition. Surge test was peformed to confirm the healthy of turn insulation in stator windings. This test is very easy to detect the turn insulation failure between normal and defect stator windings. After completing the diagnostic test, ac breakdown test has conducted gradually increasing ac voltage, until the stator winding punctured. No. 5 stator windings failed near rated voltage of 18.9 kV The breakdown voltage of No. 1 stator windings was 13.0 kV The ac breakdown voltage of normal winding is about 1.45 times higher than that of defect windings. The failure was located in a line-end coil at the exit from the core slot.

High temperature superconductor (HTS) has found its way into both AC and DC transmission. Since modeling for critical characteristic parameters of HTS in DC circumstance is a hotspot in recent years, research on the critical current of the AC condition is still scarce; a new AC critical current criterion should be established prior to further studies. In this paper, we adopt different DC critical current measurement methods to AC analysis. In alternating current the E-I curve is obtained by four-probe method when the frequency ranges from 30Hz to 810 Hz. The AC current carrying capacity of the superconductors is discussed and analyzed by the RMS method, virtual n value method and the loss concept method. We find that the methods of RMS and virtual n value are no longer applicable in the selected frequency band, while the loss concept method is applied to explain theory of critical current which varies with frequency, therefore an AC critical current calculation method is obtained and the calculative equation at different frequencies is established.

This paper presents the results of investigations recently done by our research group that improve the properties stability of GMI sensors by exploring the giant magneto-impedance (GMI) and the GMI-hysteresis of Co67Fe4.5Cu1Si12.5B15 amorphous thin strips, which was the most promising soft magnetic material could be used in the weak magnetic transducers. The amorphous thin strips were prepared by the so-called planar flow casting technology. With the circumferential driving mode, the changes of the GMI on the frequency of the ac current under different external magnetic field were measured on Agilent 4294A precision impedance analyzer. The maximum GMI ratio of 201.4% was observed. The field sensitivity, (δZ/Z)/δH, has reached 413.2%. Additionally, the ratio of GMI changes of the CoFeCuSiB amorphous thin strips could be control under 1%, by the optimum parameters of this amorphous strip, such as the DC current and the time of joule current annealing, the dc level and frequency of the excitation current, the driving method.

To assess the degradation of stator winding insulation in high voltage motor, a total of forty-eight coils were manufactured. These coils are classified into five groups and there are twelve strands in each coil. Four coil groups are artificial defects such as shorted turn of strand, internal separation between conductor and insulation, large void within insulation and removal of semi-conductive tape. The other coil group is normal. Before ac breakdown test was performed, nondestructive test that included ac current, dissipation factor and partial discharge (PD) was done with five coil groups. This paper carried out by comparing the results between nondestructive test and ac breakdown test. When the values of ac current increase rate, tip-up dissipation factor and PD magnitude are large, the insulation is occurred the deterioration. AC breakdown voltage is also low in degraded insulation.

Alternating current (AC) corrosion of mild steel in marine environments under cathodic protection (CP) condition was studied. Electrochemical studies at the two protection potentials namely −780 and −1100 mV versus SCE were examined by different techniques. DC polarization study was carried out for mild steel in natural seawater and 18.5 g/L NaCl solution to evolve corrosion current density. The corrosion rate determination, pH of the end experimental solution and surface morphology of the mild steel specimens under the influence of different AC current densities were studied. The amount of leaching of iron into the solution was estimated using inductively coupled plasma spectrometry. All these techniques revealed that AC influences the corrosion of mild steel in the presence of marine environments even though CP was given. Surface micrographs revealed that spreading of red rust products noticed on the mild steel surface. At −780 mV CP, red rusts are visually seen when the AC source was above 10 A/m 2 in both the media but red rusts are appeared after 20 A/m 2 in the case of −1100 mV CP. Weight loss measurements coupled with surface examination and solution analysis is a effective tool to characterize and quantify the AC corrosion of mild steel in marine environments.

A power source is presented capable of providing ac currents with amplitudes of up to 50 A and frequencies near 10 kHz. The current amplification is actively stabilized and exhibits fractional current noise better than one part in 105. The source was developed for use with an atom interferometer based on magnetically trapped condensate atoms. The relationship between current noise and interferometer noise is developed, and it is shown that the demonstrated precision should permit interferometry with coherence times of 1 s or more.

Design of electrical mathematics and evaluating results of the course are described in this paper. The design was carried out based on the analysis using questionnaires done to the third grade students in Iwate University. One of the analysis results with the questionnaires, many student feel the difficulty to understand in treatment of sinusoidal ac current and voltage with employment of complex numbers. Based on the analysis, the content of electrical mathematics was designed with focusing easy to use the mathematical technique to solve problems in electrical circuit and/or electromagnetic. The designed electrical mathematics was carried out in Iwate University and was evaluated by tests and questionnaires. The results showed the designed electrical mathematics contributed toward well-understanding the electrical circuits and/or the electromagnetics for students.

A gap arrester is being used for ground fault protection in AC Feeding System. However there are faults in which a conventional gap arrester burns down in a normal state of circuit. We investigated the cause of the fault in which a gap arrester burns. Then, it was found out that the cause of the fault was the discharge of AC current from the surge voltage. Therefore, we developed a new type gap arrester which does not burn down. The new type gap arrester is composed of a discharge tube and a zinc oxide element which are connected in series. Unnecessary AC current discharge is prevented by this structure. The new type gap arrester is actually used at the railroad track.

Bi2223 high temperature superconductor (HTS) tapes are expected to be used in power industry such as fault current limiter, transformer, magnets, transmission cables. For most of applications of Bi2223 tapes, the superconductor will transport ac current and/or be exposed to applied magnetic field. AC loss is one of important parameters to evaluate the economic feasibility of HTS ceramic superconductors in those applications. Extensive investigations have been done to understand the mechanism of generation of AC loss and minimize it. In this study, AC losses in Bi2223 (HTS) tapes were measured at 77 K. The effects of different factors, such as, current distribution, heat recycling, transport current wave and applied DC magnetic field, were investigated on the AC losses in Bi2223 HTS tapes. Possible explanations were presented in the paper.