DC Current Measurement Research Articles

Novel Fault Location in MTDC Grids With Non-Homogeneous Transmission Lines Utilizing Distributed Current Sensing Technology

This paper presents a new method for locating faults in multi-terminal direct current (MTDC) networks incorporating hybrid transmission media, including segments of underground cables and overhead lines. The proposed traveling wave type method uses continuous wavelet transform applied to a series of line current measurements obtained from a network of distributed optical sensors. The technical feasibility of optically-based dc current measurement is evaluated through laboratory experiments using Fiber–Bragg Grating sensors and other commercially available equipment. Simulation-based analysis has been used to assess the proposed technique under a variety of fault types and locations within an MTDC network. The proposed fault location scheme has been found to successfully identify the faulted segment of the transmission media as well as accurately estimating the fault position within the faulted segment. Systematic evaluation of the method is presented considering a wide range of fault resistances, mother wavelets, scaling factors, and noisy inputs. Additionally, the principle of the proposed fault location scheme has been practically validated by applying a series of laboratory test sets.

Digitally Controlled AC Current Measurement and Protection Techniques

Abstract This paper describes a cost effective AC current measurement method that avoids complex AC to DC current measurements by converting an amplified and rectified AC voltage drop across a shunt resistor to a duty cycle of a PWM signal. The current measurement chain output is fed into a microcontroller unit (MCU) and into a short circuit protection block that inhibits AC load drivers in case of overcurrent or short circuit events, overriding the state set by the MCU control algorithm. The authors present a mathematical model, simulations and a practical evaluation of custom-developed circuits that are capable to reach a convincing level of measurement precision. By counting a given number of consecutive AC periods, the effect of inrush current generated by inductive AC loads is filtered. The proposed solution allows inrush currents up to 3A, fitting the consumption range of AC control elements met in household application circuits, such as relays or solenoid valves.

Hardware And Software For Improving Quality Of Precise Power Supplies For Large Physical Installation

There are presented hardware, software and testing algorithms allowing improve the quality of production of the current sources for physical installations. Developed test system monitors main current source parameters and detects different defects of production and tuning. The multichannel system for measurement of DC current has the range drift less than 3 ppm/°C. Using of presented hardware and software is reviewed on the testing power supplies for European XFEL.

Accurate DC Current Ratio Measurements for Primary Currents up to 600 A

A setup based on a direct current (dc) comparator, typically employed in high-current low-resistance calibrations, has been developed for the accurate calibration of dc current ratios for dc currents up to 600 A. For primary currents above 100 A, multiple turns of the primary conductor are made through the device under test. A full uncertainty analysis reveals that the 1 part in 10 <sup xmlns:mml="http://www.w3.org/1998/Math/MathML" xmlns:xlink="http://www.w3.org/1999/xlink">6</sup> total expanded uncertainty (k = 2) in a calibration of a zero-flux device is limited by the behavior of the device, in particular the instability and sensitivity to the position of the primary current conductor.

Giant-Magnetoresistance-Based Galvanically Isolated Voltage and Current Measurements

Nowadays, dc current is much more widely used than a decade ago, not only in the well-known high-voltage dc transmission but also as dc-powered marine systems, dc data centers, and dc fast charging systems for electric vehicles. However, galvanically isolated dc voltage or current sensors are, in terms of accuracy, noise level, or dimensions, still far behind the ac measurement devices in low and medium voltage areas. In this paper, a giant-magnetoresistive-based sensor system for galvanic isolated dc current and voltage measurements is introduced. The system mainly consists of a special coil arrangement with low inductance for voltage measurement, a special U-turn for current measurement, and A/D converters with a low-cost field-programmable gate array for signal conditioning. The sensor system showed an outstanding measurement accuracy of 0.3% for voltage values up to ±550 V and 0.2% for current values up to ±100 A in a temperature range from −30 °C to 90 °C. This completely new approach for the galvanically isolated measurement of electric voltage and current avoids the use of bulky magnetic components and expensive power-consuming analog electronics, which allows one to integrate it in the current ac measure unit for power monitoring.

Electric and pyroelectric properties of AlN thin films deposited by reactive magnetron sputtering on Si substrate

Electric and pyroelectric properties of AlN layers deposited on Si substrates with different resistivities were investigated. The dielectric constant was found to be around 12, while the conductance determined from dc current measurements was found to be in the 10−9 to 10−10S range. The pyroelectric measurements were performed in voltage mode using two types of IR sources: a laser diode with 800nm wavelength and a black body at 700°C. A peculiar behavior was observed for the signal recorded when the laser diode was used as IR source. It was found that the Si substrate is introducing a signal component, due to the photogenerated carriers, which is adding to the pyroelectric signal generated by the AlN layer. This component is strongly dependent on the resistivity of the Si substrate. For strongly doped Si (Si++) the signal generated into the substrate represents only 10% of the recorded pyroelectric voltage. For electronic grade Si the signal generated into the substrate is about 100 times larger than the pyroelectric signal generated in the AlN layer. This effect can be used as an optical amplification of the pyroelectric signal. The frequency dependence observed for the pyroelectric signal recorded when the black body is used as IR source is typical for a pyroelectric detector. A value as large as 12.4μCm−2K−1 was obtained for the pyroelectric coefficient using for estimation the constant signal at low modulation frequencies of the IR beam. However, the value of the pyroelectric coefficient is strongly affected by the electrical conductance of the AlN layer. As the conductance is frequency dependent it results that the value of the pyroelectric coefficient is frequency dependent, the value from above being valid only for very small frequencies of the temperature variation. It was also found that the electric and pyroelectric properties are dependent on the crystalline quality of the AlN layer.

Study of the Interface Layer Between Lithium Metal and a Single Ion Conductor Ceramic, Based on Block Copolymer, for Lithium Air Batteries

The electrification of transport is a formidable challenge, however the energy storage possible in Li ion batteries is not sufficient to this purpose. A potential option is Lithium-air battery, first because of their very high energy densities and second because of their low costs. Two different approaches to the development of these batteries are possible: the anhydrous system which uses an organic electrolyte, and the aqueous system which uses an aqueous electrolyte [1]. An advantage of the aqueous system is its safety since toxic or inflammable solvents are not used. In order to protect the negative lithium electrode from the aqueous electrolyte, a thin ceramic water and gas tight membrane is used. The interface between the lithium metal and the ceramic membrane plays an important role in the cycling performance of the aqueous lithium air cell. Nonetheless, the poor or non-chemical stability of most ceramic electrolytes in contact with lithium metal limits the performance. A possible strategy to improve the interface between ceramic electrolyte and lithium metal might be by the use of polymer membranes [2]. This study reports the effect of a polymer membrane between a ceramic electrolyte and lithium metal. Block copolymer electrolytes, such as polystyrene-block-poly (ethylene oxide) copolymer electrolyte (SEO) mixed with lithium bis(trifluoromethanesulfonyl) imide (LiTFSI) salt, were used. The single ion conductor ceramic electrolyte was a Lithium Ion Conducting Glass Ceramic (LICGC) purchased from Ohara Corporation (1 inch X 1 inch 150µm thick). Impedance spectroscopy has been used, so as to study the lithium ion - lithium metal transfer from a lithium ion conducting polymer interface. Furthermore, in order to know if the sandwich polymer-ceramic cell showed an additional interfacial resistance, ionic conductivity experiments using electrochemical impedance spectroscopy were performed. Besides, polarization loss quantification at a lithium ion conducting polymer/single ion conductor interface was studied by DC current measurement by the Srinivasan et al method [3]. Finally, in order to confirm the intimacy of the ceramic and the polymer, the interface between the ceramic and the polymer was studied by synchrotron hard X-Ray micro tomography experiments on symmetric lithium-sandwich polymer-ceramic cells. P.G. Bruce, S. A. Freunberger, L. J. Hardwick, J-M. Tarascon, Nature Materials, 11, 19-29 (2012)G.M. Stone, S.A. Mullin, A.A. Teran, D.T. Hallinan, A.M. Minor, A. Hexemer, N.P. Balsara, Journal of the Electrochemical Society 159(3) A222-A227 (2012)Mehrotra, P. N. Ross, V. Srinivasan, Journal of the Electrochemical Society, 161 (10) A1681-A1690 (2014)

Charge collection in Si detectors irradiated in situ at superfluid helium temperature

Silicon and diamond detectors operated in a superfluid helium bath are currently being considered for the upgrade of the LHC beam loss monitoring system. The detectors would be installed in immediate proximity of the superconducting coils of the triplet magnets. We present here the results of the in situ irradiation test for silicon detectors using 23GeV protons while keeping the detectors at a temperature of 1.9K. Red laser (630nm) Transient Current Technique and DC current measurements were used to study the pulse response and collected charge for silicon detectors irradiated to a maximum radiation fluence of 1×1016p/cm2. The dependence between collected charge and irradiation fluence was parameterized using the Hecht equation and assumption of a uniform electric field distribution. The collected charge was found to degrade with particle fluence for both bias polarities. We observed that the main factor responsible for this degradation was related to trapping of holes on the donor-type radiation-induced defects. In contrast to expectations, along with formation of donors, acceptor-type defects (electron traps) are introduced into the silicon bulk. This suggests that the current models describing charge collection in irradiated silicon detectors require an extension for taking into account trapping at low temperatures with a contribution of shallow levels. New in situ irradiation tests are needed and planned now to extend statistics of the results and gain a deeper insight into the physics of low temperature detector operation in harsh radiation environment.

Pump-Probe Noise Spectroscopy of Molecular Junctions.

The slow response of electronic components in junctions limits the direct applicability of pump-probe type spectroscopy in assessing the intramolecular dynamics. Recently the possibility of getting information on a sub-picosecond time scale from dc current measurements was proposed. We revisit the idea of picosecond resolution by pump-probe spectroscopy from dc measurements and show that any intramolecular dynamics not directly related to charge transfer in the current direction is missed by current measurements. We propose a pump-probe dc shot noise spectroscopy as a suitable alternative. Numerical examples of time-dependent and average responses of junctions are presented for generic models.

Analysis and Test of a Zero-Flux Current Sensor to Be Used in ITER

A zero-flux current sensor to be used in International Thermonuclear Experimental Reactor for large DC current measurement is researched and developed. A magnetic flux equilibrium equation based on linearity assumption is introduced to predict its operating parameters. The analysis is done by 3D finite element method and greatly simplified with the help of the sensor’s characteristic matrix. Corresponding experimental tests are also performed on a prototype and the results fit very well with the computed ones. And the sensor’s measurement accuracy and compatibility against external field noise have also been proved by the test results.

A Protection Scheme of Ac Side Faults of Dc Distribution System

Dc distribution systems are multiterminal systems characterized by complexity and mixed operation of ac and dc. Ac side faults are more likely to happen and may cause more serious consequences compared with dc transmission systems, thus must be considered seriously. In this paper, ac side faults of the prototype dc distribution system under high impedance grounding scheme are analyzed in detail. Fault characteristics of dc side voltages and currents under ac side faults are drawn and sorted. A protection scheme of ac side faults is proposed based on dc voltage and current measurements. The effectiveness of the protection scheme proposed is demonstrated by simulation under PSCAD/EMTDC.

HVDC DC CT 선형성 최적화 및 시스템 적용에 대한 연구

These days, the advantages of DC power system are consistently stand out in korea that was a small power loss and high stability. Needs of DC power transmission technology is focused In the midst of a smart grid and environment friendly generation technology boom that is needed for next generation technology. Researches and businesses for HVDC(High Voltage Direct Current) system has been began. But, Needs of HVDC equipment and system commissioning technology are not on the rise until now. In particular, South Korea’s HVDC technology is after the foot runner of advanced country and company. In addition, There is no experience for equipment verification and commissioning technology. And Experts of HVDC are rare. Who has been fully understood hardware and system as a whole, and identified all the equipment’s characteristic. Recently, Academia and industry are recognized a needs of HVDC technology. But it does not received a recognition of technical value. In this paper, introduce issues when we apply the IEEE’s verification method for HVDC system, especially DC current measurement system, DC CT(Direct Current Transformer), among the HVDC equipments. And Proposes remedial methods on the issue in order to recognize the necessity that was HVDC equipments’s verification and commissioning technology research should be focused on.

High-Bandwidth High-Temperature (250 °C/500 °F) Isolated DC and AC Current Measurement: Bidirectionally Saturated Current Transformer

In an increasing number of application areas and industry sectors, such as the automotive, aerospace, military or oil and gas industry, a trend towards higher ambient temperature rating from 85 °C upwards for electrical machines and power electronic converters can be observed. To reduce the impact of high ambient temperatures on the power density, the interest in power electronic converters with SiC power semiconductors operated up to a junction temperature of 250 °C rises. The control of power electronic converters typically requires a precise, fast, and robust current measurement. However, analyzing current measurement concepts from the literature reveals that there is a lack of measurement systems, that are galvanically isolated and able to measure dc and higher frequency ac currents fast at high ambient temperatures of 250 °C. In this paper, a current measurement concept of a bidirectionally saturated current transformer is presented, that is able to measure dc and sinusoidal ac up to 1 kHz and 50 A at an ambient temperature of 250 °C with an relative error of 2.6% and less than 0.5% error after initial calibration. Furthermore, a prototype is designed, built, and used for the experimental verification of the concept.

DC current measurement utilizing a resonant magnetically actuated piezoresistive microcantilever

This paper presents a novel current sensor by using a resonant piezoresistive microcantilever combined with magnetic actuation for the first time. An actuation power of several microwatts was necessary for stable self-oscillation. The sensor measured the DC current by obtaining the electrothermally induced resonant frequency shift of the microcantilever as a result of the Joule heating dissipated when the DC current flowed through the Wheatstone bridge on the microcantilever. Two theoretical models were established between the microcantilever's resonant frequency and the square of the DC current. The experimental results showed that the accuracy in the range of 0.5–5 mA (apart from 0.5 mA) using the two models was 2.60% and 1.00% with correlation coefficient value R > 0.999 in both cases, respectively. The current sensitivity of the sensor was about −3.983 Hz mA−2 in the range of 0.5–5 mA. To maintain stable results, the sensor chip should be sealed in vacuum and integrated into an oven-control system.

Development of an in situ calibration method for current-to-voltage converters for high-accuracy SI-traceable low dc current measurements

For photocurrent measurements with low uncertainties, wide dynamic range reference current-to-voltage converters and a new converter calibration method have been developed at the National Institute of Standards and Technology (NIST). The high-feedback resistors of a reference converter were in situ calibrated on a high-resistivity, printed circuit board placed in an electrically shielded box electrically isolated from the operational amplifier using jumpers. The feedback resistors, prior to their installation, were characterized, selected and heat treated. The circuit board was cleaned with solvents, and the in situ resistors were calibrated using measurement systems for 10 kΩ to 10 GΩ standard resistors. We demonstrate that dc currents from 1 nA to 100 µA can be measured with uncertainties of 55 × 10−6 (k = 2) or lower, which are lower in uncertainties than any commercial device by factors of 10 to 30 at the same current setting. The internal (NIST) validations of the reference converter are described.

Focus on semiconductors and software

Focus on semiconductors and software

A heterostructured SnO2–TiO2 thin film prepared by Langmuir–Blodgett technique

SnO2–TiO2 heterostructure films were prepared through Langmuir–Blodgett (LB) route. LB films of octadecyl amine (ODA)–titanyl oxalate multilayer deposited on Si (100) and decomposed at 600 °C showed rutile and anatase phases of ultrathin TiO2 film. Subsequently, multilayer LB film of ODA–stannate deposited on the pre deposited TiO2 film after decomposition at 600 °C resulted in thin SnO2 films on the TiO2 thin film. The phase analysis of the SnO2–TiO2 film showed cassiterite phase of SnO2 as well as the rutile/anatase mixture of TiO2 indicating a SnO2–TiO2 heterostructured film. Surface morphology of the pure TiO2 film and SnO2–TiO2 film were analyzed by using AFM. Electrical characterization by AC impedance analysis suggested SnO2–TiO2 heterostructure formation. DC current voltage measurement showed increase in photocurrent indicating visible light absorption and efficient charge separation under the sunlight type radiation.

IV Transport Critical Current and n Number of MgB2 Conductors as a Function of Temperature

IV data of MgB2 conductors were obtained over more than 3 voltage decades from 0.1 to 400 μV/cm and currents up to 600 A, revealing the characteristic <i xmlns:mml="http://www.w3.org/1998/Math/MathML" xmlns:xlink="http://www.w3.org/1999/xlink">n</i> number to increase rapidly with decreasing temperature from <i xmlns:mml="http://www.w3.org/1998/Math/MathML" xmlns:xlink="http://www.w3.org/1999/xlink">n</i> = 20 around 33 K to above 60 by 25 K. Constant temperature, current-voltage, ( <i xmlns:mml="http://www.w3.org/1998/Math/MathML" xmlns:xlink="http://www.w3.org/1999/xlink">IV</i> ) characteristics of magnesium diboride conductors over a sufficient voltage range to determine <i xmlns:mml="http://www.w3.org/1998/Math/MathML" xmlns:xlink="http://www.w3.org/1999/xlink">n</i> are not available in the literature and remain a serious experimental challenge. Conductors, instrumented with voltage and temperature sensors, were mounted on a cryofree, variable-temperature-controlled platform within a custom built cryostat. To achieve constant temperature measurement, the stability had to be improved by reducing the thermal path either longitudinally or laterally. Both dc current and transient measurements were implemented and refined until good agreement was obtained. At the highest stable voltage reached, for a given temperature, any further increase led to a rapid thermal propagation until the sample was fully resistive. In carbon-doped samples, the temperature-dependent transport critical current density is best described by two linear functions with different <i xmlns:mml="http://www.w3.org/1998/Math/MathML" xmlns:xlink="http://www.w3.org/1999/xlink">T</i> <sub xmlns:mml="http://www.w3.org/1998/Math/MathML" xmlns:xlink="http://www.w3.org/1999/xlink">c</sub> 's. The lower <i xmlns:mml="http://www.w3.org/1998/Math/MathML" xmlns:xlink="http://www.w3.org/1999/xlink">T</i> <sub xmlns:mml="http://www.w3.org/1998/Math/MathML" xmlns:xlink="http://www.w3.org/1999/xlink">c</sub> function has the steeper increase in transport critical current with decreasing temperature.

Measurement of DC Currents in the Power Grid by Current Transformer

DC currents in power grids are mainly caused by geomagnetic activity especially during magnetic storms. It is desirable to monitor these currents to prevent saturation of transformers, which may cause blackout. However, adding DC current sensors to existing installations would be very costly. We suggest to convert some of the existing current transformers to fluxgate DC current sensors by injecting AC excitation current into their secondary winding. We successfully tested this concept on 500 A current transformer. The achievable accuracy is 10% for DC currents and 1.5% for AC currents, which is sufficient for protection and monitoring purposes. We analyze the DC current sensitivity dependence on the (changing) grid impedance, and we show that the sensitivity can be stabilized by controlling the secondary voltage component at the excitation frequency. Excitation current injected into the grid also depends on the grid impedance, but for realistic conditions it is below 2 A.

Neel Effect Toroidal Current Sensor

In this paper, a configuration for a Neel effect ac-dc current sensor designed with second harmonic sensing in view is proposed. This configuration relies on the use of two toroidal superparamagnetic cores wound in opposite direction with respect to each other and connected in series. An analytical model is developed, which shows that the component of the output signal at the excitation frequency, which is useless, should be removed provided that the windings are symmetrical. The latter principle is validated experimentally and a prototype device is characterized for different excitation conditions. Open loop dc and ac current measurements are carried out over the [-110 A, 110 A] range.