AC Current Measurement Research Articles

Magnetic sensors for contactless and non‐intrusive measurement of current in AC power systems

AbstractThis paper reports the results of an investigation into the use of magnetic sensors for measuring AC currents and subsequently, estimating AC current phasors in low‐ and medium voltage AC power systems. Tunnelling magnetoresistive (TMR) sensor of high sensitivity and a wide range was used for the magnetic field measurement around AC conductor. The sensor was calibrated to overcome the inequality in the sensed magnetic field due to various aspects such as the distance from the source, minute structural variations, the magnitude of the source current, and presence of harmonics. Performance was tested for accuracy at lower frequencies such as 1, 2, 5 and 10 Hz as well as at higher frequencies such as 2nd, 3rd, 4th and 5th harmonics of the fundamental frequency. The percentage total vector error (TVE) was calculated for current phasors with input current magnitudes varying from 5 to 1500 A of various frequencies and was compared with the actual current as well as with the outputs of a high accuracy conventional core‐wound donut type current transformer (CT). The measurement accuracy corresponding to magnitude, phase and TVE during laboratory and field applications validated the suitability of TMR sensor for contactless and non‐invasive AC current measurement.

Non-Invasive Measurement of Impedance Spectra Distribution in Polymer Electrolyte Fuel Cells

Localized measurement of the impedance distribution in an operating polymer electrolyte fuel cell stack is of great importance in providing information on its state of health and performance. However, the current methods’ invasiveness is a brake to a more widespread utilization. This work presents a non-invasive way to measure and interpret local impedance spectra. It is based on local AC current supply and local voltage measurements performed all around the cell via conductive pins contacting the outer surface of the flow fields. The different local spectra are measured on a single cell within a 200 cm2 six-cell stack under different operation conditions and compared to a reference case with homogeneous current density. A simple equivalent electrical circuit is used to fit the impedance spectra and to extract membrane and charge transfer resistance. The variations of these two values are analyzed at five different positions along the channel for different cathode stoichiometries and gas flow configurations.

Noninvasive Local Impedance Determination in Polymer Electrolyte Fuel Cells Stacks

Water management in polymer electrolyte fuel cells (PEFC) needs to ensure a homogeneous membrane humidification without local dryout or flooding from inlet to outlet of cell with active areas of some hundreds of square centimeters. Measurement methods that are able to provide spatial resolved information on the current density, membrane conductivity or water content distributions of PEFCs are usually invasive and therefore difficult to use in actual applications. Based on the learnings of the development of electrical impedance tomography (EIT) for PEFCs [1], a new method is presented that is capable to determine 1D humidity profiles between the gas inlet and outlet in a 6-cell commercial stack [2,3]. Local AC current injections and voltage measurements are performed using electrodes positioned all around the fuel cell attached to the flow field plates (see Figure 1a). Each electrode combination characterizes a specific area of the cell as the current crosses the membrane electrode assembly (MEA) very locally.The presentation will discuss the calibration of the local impedance values, the sensitivity of the approach to relative humidity (rH) gradients in the cell (see Figure 1b) and present use cases of measurements during fuel cell operation. Finally, we will present results on multiply frequency AC stimulation that allows local electrochemical impedance measurements and thereby insights beyond membrane conductivity, i.e. into mass transport limitations due to water accumulations in the cell.

Influence of coaxial cable resistance on impedance measurements at low frequency and guidelines for phase determination of ac electrical signals.

We present an experimental study on ac measurements at low frequencies (below 1MHz) when the coaxial cables used for the measurement are resistive, as in cryogenic conditions. More precisely, we are interested in admittance or impedance measurements and the accurate determination of the phase. Our experiments were completed using an auto-balancing bridge impedance analyzer and various standard coaxial cables, as well as their serial combinations. We characterize the experimental setup, and then, we analyze and measure the phase shift introduced in impedance measurements by lead resistance. Using basic equations for electrical signal propagation in coaxial cables, we calculate phase shift in the whole frequency range and explain our data in the low frequency limit of our model. We propose a quantitative criterion to determine whether the experimental context is appropriate. If not, we show that by using an original calibration procedure, the imaginary part can be accurately recovered, avoiding artifacts. The calibration procedure can be applied to any ac voltage or current measurement, whatever the detection technique is, with known accuracy.

Calibration of a precision current measurement system for high AC voltages using an AC quantum voltmeter

This paper describes the calibration of a high precision AC current measurement device which is required in a system to measure AC voltages up to 800 kV in the frequency range of 10 Hz to 400 Hz. The AC current measurement unit of such a system requires the calibration of the input current in the milliampere range at a frequency of approximately 50 Hz, and all measurements have been made at a suitable frequency of 62.5 Hz. An AC quantum voltmeter (AC-QVM) is used to achieve a traceability chain from DC resistance calibration, when it works as DC quantum standard, and as AC quantum standard for the AC current measurement. All DC and AC measurements needed for one calibration point (one current level) can be done in a rapid sequence within 30 min using the same AC-QVM, such that the combined uncertainty is at a level of 1 μA A−1 (k = 1).

The Testing Of High Voltage Silicon Carbide Lightning Arresters

The majority of high voltage gapped silicon carbide lightning arresters on transmission and sub transmission systems have been in service for over 10 years. A testing program is required that can accurately and efficiently determine the condition of these high voltage arresters. The essential theory of silicon carbide arresters was investigated, focusing particularly on arrester construction, performance and the unique characteristics of high voltage arresters. The effectiveness of available testing procedures was then evaluated and a set of tests selected, based on their expected performance, their ability to assess all facets of arrester behavior, the ease with which they could be completed in the available laboratory and their possible application to in-field testing. The testing program implemented consisted of a series of procedures including the lightning impulse sparkover voltage test, power frequency sparkover voltage test, power frequency withstand test, AC and DC leakage current measurements, 5 kV insulation resistance test, and finally a non-standard current impulse test. The tests were performed on a set of 6 arresters rated at 33 and 132 kV and a set of 5 arrester sections. The results of the investigation verified the effectiveness of the selected procedure with a consistent and accurate assessment of arrester condition obtained for all arresters under test. All arresters exhibited satisfactory performance in the selected tests, indicating that high voltage gapped silicon carbide arresters are more durable than those used on distribution systems.

A non-contact broad bandwidth current sensor

Power metering, relay protection, lightning current measurement, fault current measurement, and traveling current measurement in the field of power systems, as well as high-current measurement in the field of pulse power, require safe, high-accuracy, large-range, and wide-frequency-band current sensors. Current transformers and Rogowski coils can basically meet the requirements of measurement accuracy and range, but they are not good enough to meet the two requirements of safety and broad frequency bands. In this study, a non-contact broad-band current sensor is designed, which is based on the improvement of the traditional Rogowski coil to realize non-contact measurement of current. The equivalent circuit of the sensor was established, and the output characteristics of the sensor were calculated from the theoretical level as well as the design parameters were optimized. The sensor samples were made, and the usability of the sensor and the correctness of the theoretical calculation model were verified by 50 Hz AC current and 1.6 μs/3.4 μs impulse current tests. The non-contact current sensor designed in this paper has the advantages of simple structure, low cost, safety and reliability, large range, and wide operating band, and can be widely used for AC current or impulse current measurement in power systems and pulsed power fields.

Blood Coagulation Time Determination by AC Current Phase Shift Measurement

Blood Coagulation Time Determination by AC Current Phase Shift Measurement

Noninvasive Measurement of Conductivity Distribution in Polymer Electrolyte Fuel Cells (PEFCs)

Water management in Polymer Electrolyte Fuel Cells (PEFCs) is a crucial topic. Indeed, a homogeneous distribution of the water in the membrane plane is important as it dictates its conductivity. Furthermore, local dry outs or flooding event can damage the cell. Existing measurement methods that are able to provide spatially resolved information on the current density, conductivity or water content distribution are usually invasive and therefore difficult to use in actual applications. A new method, based on the learnings of the development of Electrical Impedance Tomography (EIT) for PEFCs [Schuller and Eller 2020 ECS Trans. 98 3], is used to determine 1D humidity profiles between the gas inlet and outlet in a 6-cell commercial stack. Local AC current injections and voltage measurements are performed using electrodes positioned all around the fuel cell. Each measurement characterizes a defined area of the membrane as the current crosses it very locally. In a first step, the method is calibrated using nitrogen flow at different well-defined humidity levels. Using the calibration data the local boundary voltages can be converted into local humidity conditions when the stack is operated. In Figure 1a the reconstructed conductivity distributions of the stack being operated at four different current densities with inlet relative humidity (RH) of 60 % at the anode and 30 % at the cathode in counter flow configuration is shown. The y-axis represents the relative membrane conductivity value where 1 corresponds to the reference measurement with the highest inlet RH (90%). The conductivity increases with increasing current densities and there tends to be a higher conductivity towards the cathode outlet due to water drag through the membrane. Thanks to the fast multi-channel data acquisition setup, the method can be also used to study the dynamic behavior of a cell. Figure 1b shows the time resolved reconstruction of the conductivity distribution when flushing the cell with nitrogen (anode and cathode at 40% RH) after the stack is operated at 0.8 A/cm2. The method is capable to resolve the quick decrease in membrane conductivity at both inlets and to follow the much slower drying process of the membrane in the center of the cell. Figure 1

Development of Electrical Quantities Primary Standards

The developments of primary standards for electrical quantities that practically realize the electrical units such as ampere (A), volt (V), ohm (Ω), and farad (F) are introduced in this manuscript. These quantities are achieved in consistency with their definitions. According to the new definition of ampere, current can be realized directly such as single electron transport (SET) pump or indirectly using Ohm’s law. For the SET pump, developments are ongoing as trials to obtain higher current values with lower associated uncertainty to be suitable for metrological applications. With the discoveries of the Effects of Josephson and quantum Hall, it has become possible to consider quantum electrical standards that relate the volt and ohm units to h and e through the Josephson and the von Klitzing constants, respectively. The dc programmable Josephson standard was developed to overcome the problems of conventional standards such as stability and noise immunity with lower cost. Developments are continuing on ac Josephson standards to improve performance and increase output voltages and frequencies. For ac voltage measurements for voltages up to 1000 V, thermal voltage converters are introduced to extend the traceability for measuring the ac voltages in the frequency range from 10 Hz to 100 MHz where quantum-based ac standards still have limitations. Thermal current converters are used as the most accurate and precise standard for measurement of ac currents. The realization of ohm is done by the quantum Hall effect through a quantum Hall resistance (QHR) standard. Developments are occurring to make it simpler, more precise and accurate. The efforts that have been made to increase the values of the resistance quantum hall standard to disseminate its accuracy to other standard resistors to help in industry are also introduced. The farad is practically achieved by the calculable cross-capacitor. The calculable capacitor acts as the ac impedance primary standard because it can transfer the traceability to other impedances by using bridges such as the quadrature bridge. The development is occurring on its displacement sensing system to allow greater accuracy.

Easy monitoring and data record system of electric current detected by ACS712 affordable non-destructive electrical current sensor

Monitoring and data record system of electric current on the current conducting wire has been developed. Recently, the current measurement was conducted by electronic circuit configuration by adding the shunt resistance in the circuit configuration . Compare to the voltage measurement, the electric current measurement has several obstacle and sometimes dangerous, especially on the AC current measurement. This study offers the automation of electric current measurement using affordable and non-destructive ACS712 Hall effect sensor. Hall effect is the phenomena of charge flow deflection in the metal plate that is placed in the magnetic field. By using this sensor, it is possible to detect the AC and DC current on conducting wires. The output of the sensor voltage will be change based on the magnetic field obtained due to current flows in the wire. Those output voltage are processed in microprocessor of ATMEGA238. Measurement results are saved in *.txt format. LabVIEW is used as the display system interface to simplify the utilization . The measurement is conducted in the Faraday cage. This system can be one of answer for the efficient and stable affordable current measurement with the precision is 0.9954 and average of accuracy percentage is 99.5934%. To reach those precision, the sensor calibration formula in datasheets should be corrected by subtracts the sensor calibration formula with the constant of 0.125.

UNCERTAINTY EVALUATION ON THE CALIBRATION OF DC & AC CURRENT GENERATED BY COMBINATION OF AC/DC CURRENT SOURCE AND CURRENT COIL USING SUBSTITUTION METHOD

Development of measurement method for calibrating current coil continues to be made to maintain measurement traceability for high DC and AC current scope which are generally used for clamp meter calibration services in Laboratory of National Measurement Standard for Electricity and Time (Lab NMS ET). This paper describes the uncertainty evaluation method developed in Lab NMS ET for calibrating high DC and AC current from 50 A up to 990 A generated by a single system consisted of a DC/AC current source and a 50-turn current coil. The uncertainty analysis was carried out based on the calibration principle using the substitution method combined with the principle of multiplication between output current of a DC/AC current source and a 50-turn current coil. It resulted in six source of uncertainty component derived from the current source, the current coil, and a meter. Their sensitivity coefficients were calculated as well to adapt the unit of each uncertainty budget to the final unit in Ampere (A). Using this uncertainty evaluation principle, at the measuring range of 50 A to 990 A, the expanded uncertainties for DC current were spanned from 0.69% to 1%. As for AC current, they were spanned from 0.8% to 1.4%. The major uncertainty contribution comes from the current coil which is representation of uncertainty due to various factors affecting the current coil performance. Validation had been carried out and the normalized error (EN number) values were in the range -0.48 to -0.16 for DC current measurements and in the range of -0.06 to 0.16 for AC current measurements.

Low-Frequency Characteristics of Silicon-Based High-Current Multijunction Thermal Current Converters Fabricated by Wet Chemical Etching

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.

High Precision Wide Bandwidth DC Current Transducer Based on the Platiše Flux Sensor

In the last decade, we observed a noticeable increase in direct-current systems (DC), particularly in solar power generation, grid storage systems, and electric mobility. Some of these systems may require high-voltage isolation and peak currents in excess of kA. The existing standard compact and lower cost current sensing solutions hardly ever achieve an overall measurement uncertainty below 1% mainly due to offsets and hysteresis; their typical bandwidth is about 250 kHz, and they may also be noisy. This article presents a new method of isolated DC and AC current measurement based on a single gapless core and the innovative Platiše Flux Sensor. After verification in a mixed-signal simulator, the method was implemented in a functional prototype of a DC current transducer (CT) and thoroughly tested in a reference setup. The performance tests showed a low offset and hysteresis, a bandwidth in the MHz range, low power consumption, and low noise operation. Furthermore, the low current transducer achieved a typical uncertainty of less than 0.2% and a linearity of less than 200 ppm, which indicates an overall superior performance compared to representative comparable CTs based on alternative technologies. In addition to the areas of application mentioned above, the new type of DC-CT can be used for general purpose metering, measurement instrumentation, and high power DC and AC systems.

Study of the influence of magnetic properties of amorphic alloys on the electromagnetic field of current transformers with a short-closed circuit

The optimal functioning of the electric power industry can be ensured only if the important problem is successfully resolved by reliable measurement of electrical quantities, such as voltage, current, and power. In industry, a current transformer is often used as a current meter, which makes it possible to obtain an AC current measurement result with high accuracy. Structurally, the current transformer has a significant drawback, which is that the opening of the secondary measuring winding leads to an emergency. To solve this problem, you can apply the improved design of the current transformer squirrel-cage current transformer (in the form of a cylinder or ring). This article presents the results of two-dimensional modeling of the electromagnetic field of current transformers with a short-circuited coil, with cores made of different grades of amorphous iron in the ELCUT software package. In addition, the results of experimental studies of the improved design of the current transformer are presented. An analysis of the results allows us to conclude that the use of a core made of amorphous iron with a higher magnetic permeability will lead to economic benefits and make the measurement process more energy efficient.

Fault Detection and Localization for Cascaded H-Bridge Multilevel Converter With Model Predictive Control

The cascaded H-bridge (CHB) multilevel converter has been used in various applications, such as the STATCOMs and solid-state transformers. Due to its modular structure, fault tolerance can be incorporated in the CHB multilevel converter. In this article, a model predictive control (MPC)-based fault detection and localization (FDL) scheme is proposed for the CHB multilevel converter that utilizes the already-installed ac current measurement and does not require additional sensors. The proposed FDL scheme can detect single or multiple open-circuit switch faults in the CHB multilevel converter by comparing the predicted states of the MPC controller with the actual measured states. The detected fault(s) is(are) further localized through a fault localization matrix which narrows down the faulty switch using historical fault data. The proposed scheme is shown to complete the FDL process for both single or multiple open-switch faults within a fundamental cycle period, even during low-load conditions. It has also been shown that the proposed scheme is immune to system dynamics such as load and voltage variations, and has been validated experimentally for various open-circuit fault scenarios.

Main Approaches to Cable Aging Management at Nuclear Power Plants in Ukraine

The mechanisms of cable ageing at nuclear power plants (NPPs) mainly depending on the insulation material, as well as the damaging factors affecting cables that are determined by the operating conditions are considered in the paper. The main and additional mechanisms of aging resulting from the effects of damaging factors are provided. The paper presents the main methods of cable aging management: determining the actual service life and testing using field methods and other means. The basic principles for the arrangement of cable aging management at Ukrainian NPPs, as well as the methods used to investigate the technical condition of cables, are presented. A list of mandatory lists has been defined when performing activities on cable aging management. A methodology is described for lifetime extension of cables, and conditions for extending the service life of cables that are in service are provided. A number of methods of testing cables for aging management are considered: visual inspection of insulation and measurement of crack size, discoloration, etc.; insulation hardness test; insulation chemical analysis; electrical insulation tests; tensile strength measurement; measurement of elongation at break; measurements of dielectric loss at low frequency or sweep frequency; testing by dynamic reflectometry method; AC and DC current impedance measurements. The paper presents results of separate laboratory studies for selected 1 kV representative power cables with PVC insulation of SUNPP-1, ZNPP-1 and KhNPP-2 conducted within Ukrainian NPP long-term operation, which included a stage of laboratory examination and examination of cable samples in operating conditions. The following results were obtained: dependence of VVGng 4x6 cable lifetime on operating temperature; dependence of AVVG cable lifetime on operating temperature; dependence of AVVG (a) cable lifetime on operating temperature. There are possibilities and conditions under which the use of cables within long-term operation is permissible.

Isothermal Kinetic Investigation of the Water-Cations Interaction in Natural Clinoptilolite

The kinetics of water adsorption by a natural zeolite (clinoptilolite) sample has been investigated by high-frequency AC current intensity measurements. According to the achieved kinetic results, cations should play a relevant role in the clinoptilolite hydration, in fact most of adsorbed water stay in the cationic sites. The water molecules associate withcation one-by-one. In particular, the forced adsorption of water molecules in a wet atmosphere is a quite slow process, while water desorption in air or dry atmosphere is a spontaneous and fast process. The observed increase of cation mobility could be adequately explained by assuming an arrangement of water molecules between the cation and the negatively charged oxygens contained in the cationic site. Such molecular arrangement could increase the strength of both dipole-cation and hydrogen bond interactions.

Isothermal Kinetic Investigation of the Water-Cations Interaction in Natural Clinoptilolite

The kinetics of water adsorption by a natural zeolite (clinoptilolite) sample has been investigated by high-frequency AC current intensity measurements. According to the achieved kinetic results, cations should play a relevant role in the clinoptilolite hydration, in fact most of adsorbed water stay in the cationic sites. The water molecules associate withcation one-by-one. In particular, the forced adsorption of water molecules in a wet atmosphere is a quite slow process, while water desorption in air or dry atmosphere is a spontaneous and fast process. The observed increase of cation mobility could be adequately explained by assuming an arrangement of water molecules between the cation and the negatively charged oxygens contained in the cationic site. Such molecular arrangement could increase the strength of both dipole-cation and hydrogen bond interactions.

Novel Broadband Calibration Method of Current Shunts Based on VNA

Usually high wideband ac current and harmonics measurements are accurately achieved in industry and laboratories by using high accuracy shunts or standard shunts. For particular applications, such as power and transient measurements, it is mandatory to evaluate the shunt impedance phase and magnitude according to the frequency bandwidth of interest before to measure the current with such sensors. High electrical current shunt beyond 1 A is calibrated in magnitude up to 100 kHz and in phase angle up to 200 kHz only by a few National Metrology Institutes. The existing traceable measurement methods to characterize these sensors are limited in frequency to 100 kHz, with expanded uncertainties of the ac–dc difference (magnitude) and the phase angle of more than $5 \times 10^{-6}$ and $62~\mu $ rad at 100 kHz, respectively. A new traceable calibration method to measure and characterize current shunts at high frequencies is presented in this paper. This measurement method is based on the use of a vector network analyzer. The measurements are presented up to 60 MHz, but theoretically, the presented method does not exhibit a specific frequency limitation. Only the characteristics of the shunt under study can impose limitation in practice. While uncertainties are higher than those provided by the existing methods, the method presented in this paper is the only method able to perform in one step a broadband and simultaneous measurement of the magnitude and phase of current shunts up to few megahertz with acceptable uncertainties.