Measurement Of Large Currents Research Articles

Current measurement method based on integral reconstruction of magnetic rotation angle

In view of the nonlinear limitation of the sine function on the magnetic rotation angle in the optical current sensor based on the light intensity detection mode, this paper proposes a current measurement method based on the integral reconstruction of the magnetic rotation angle, thus avoiding the large current measurement error caused by the approximate linear measurement of the magnetic rotation angle. In this method, the cosine term in the derivative of the sine signal containing the magnetic rotation angle is eliminated by the constant deformation of the trigonometric function, and then the magnetic rotation angle is reconstructed by integration. The experimental results show that within the current range of 0.20 Arms to 2.40 Arms, the measurement error of the current value of the integral reconstruction method is less than 1.30%, the measurement error is less than the approximate linear measurement method, and there is a good linear relationship between the magnetic rotation angle and the current, with a linearity of 99.987%.

A Novel Method for Wide Range Electric Current Measurement in Gas-Insulated Switchgears With Shielded Magnetic Measurements

Magnetic field (MF) sensing and interpretation remains an active area of research for source current reconstruction and measurement applications. One such area is large current measurement for power system components with contact less MF sensing. The output of recently made available magnetic sensors is favorable for large current measurement applications. This stimulates development of a noncontact magnetic sensor-based large electric current measurement system for fixed conductors to be employed in power systems. However, the presence of strong magnetic noise from near equipment imposes restriction on the use of sensitive magnetic sensor in open air where magnetic noise sources operating at the same frequency may distort the sensor output. The novelty of this paper is the application of MF sensor inside magnetic shielding layers for large current measurement. High-permeability Mu-metal is employed and arranged in three arc-shaped layers for designing a semicircular special shielding arrangement. The application of the method and design is demonstrated for large current carrying conductor arranged inside a gas-insulated switchgear. The measurement system is first validated by the finite-element analysis method and then tested with a comprehensive experimental setup in the presence of strong magnetic noise stimulus of 0.28 T generated by a strong neodymium magnet. The resultant apparatus is tested for current of up to 1000 A with a resolution of 0.01% and error less than 3% in the worst case scenario. The prototype demonstrated excellent linearity during experimental validation of current measurement of 100–1000 A in the presence of magnetic noise stimuli at different positions where the standard deviation between slopes value for sensor response to input current (100–1000 A) curve for six different test cases remains only 0.83%.

Impact of Coreless Current Transformer Position on Current Measurement

Magnetic sensors have been widely used for current measurements in diverse industries. In order to achieve a large current measurement without an iron core structure, magnetic sensors are often arranged to be a circular array for designing a new electronic current transformer (ECT). However, this ECT with a circular array of magnetic sensors usually suffers from tradeoffs between the number of sensors and the measurement accuracy. This paper visualizes this tradeoff and proposes a 3-D magnetic-field model to analyze the impact of the magnetic sensor circular array position on current measurements. We develop an analytical expression of the current measurement errors to estimate the minimum number of required magnetic sensors and point out the acceptable deviations of the ECT position under various accuracy classes. Based on the estimation results, we design a new circular array with eight magnetic sensors and build a three-phase current measurement system. The test results demonstrate the efficiency and the robustness of the designed class-1.0 ECT, which successfully maintains accuracy class 1.0 under various position deviations in balanced or unbalanced three-phase power delivery systems.

A Sensitivity-enhanced Fiber Grating Current Sensor Based on Giant Magnetostrictive Material for Large-Current Measurement.

Currently, in the modern power industry, it is still a great challenge to achieve high sensitivity and uninterrupted-online measurement of large current on the high voltage gridlines. At present, the fiber grating current sensors based on giant magnetostrictive material used in the modern power industry to achieve uninterrupted-online measurement of large currents on high voltage grid lines is a better method, but the sensitivity of this current sensor is relatively low, therefore, it is key to improve the sensitivity of this current sensor. Here we show a sensitivity-enhanced fiber grating current sensor based on giant magnetostrictive material (in the following, simply referred to as the sensitivity-enhanced fiber grating current sensor) that is able to achieve high sensitivity and uninterrupted-online measurement of large currents by means of pressurizing the giant magnetostrictive material. Sampling the power frequency sinusoidal alternating current signals with the amplitudes of 107, 157 and 262 A respectively, based on realistic factors, for the sensitivity-enhanced current sensor, the sensitivities, compared with that of the traditional fiber grating current sensor based on giant magnetostrictive material (in the following, simply referred to as the traditional fiber grating current sensor), were respectively enhanced by 268.96%, 135.72% and 71.57%. Thus the sensitivity-enhanced fiber grating current sensor allows us to solve the issue of high sensitivity and uninterrupted-online measurement of large currents that have been plaguing the power industry in a very simple and low-cost way.

Ratio Error Reduction of a Current Transformer Using Multiple Winding Technique

A current transformer (CT) converts the current of the primary side to the proper current level for the secondary side. Hence, the most important performance of the CT is the reliability of the current ratio. However, it is difficult to maintain a reliable current ratio when a CT is used for large current measurements in, for instance, an electric furnace or when it serves under abnormal conditions such as in high temperature applications or in limited spaces where a proper installation position cannot be guaranteed. Therefore, in the design of a CT, the realization of high reliability and robustness minimizing the transformation ratio error for diverse operating circumstances is crucial. To address these issues, a highly reliable and robust CT using a multiple winding technique is proposed. It is termed the multiple winding CT (MCT) in this paper. With the proposed analysis method, the MCT is designed for the minimization of the ratio error in this research. Moreover, the MCT is designed taking into account the temperature characteristics using a temperature analysis method. The usefulness of the proposed MCT is validated via an experiment.

Analysis of Electric Vehicle DC High Current Conversion Technology

Based on the background of electric vehicles, it is elaborated the necessity about electric energy accurate metering of electric vehicle power batteries, and it is analyzed about the charging and discharging characteristics of power batteries. It is needed a DC large current converter to realize accurate calibration of power batteries electric energy metering. Several kinds of measuring methods are analyzed based on shunts and magnetic induction principle in detail. It is put forward power batteries charge and discharge calibration system principle, and it is simulated and analyzed ripple waves containing rate and harmonic waves containing rate of power batteries AC side and DC side. It is put forward suitable DC large current measurement methods of power batteries by comparing different measurement principles and it is looked forward the DC large current measurement techniques.

USING OF DIFFERENTIATES INDUCTION TRANSDUCER FOR MEASURING HIGH CURRENTS

The use of energy saving devices that allows reducing the weight and dimensions in tens and hundreds of times of the existing electrical equipment respond the modern requirements. Replacement of current transformers by Rogowski coil allows measurement of large currents at the same voltage.

The Modern Current Sensors of Synthetic Magnetic Resin Part 3 - Transmission Characteristics and Design of the Sensor Amplifier

The article presents the results of unpublished research on the new generation current sensors, designed on the basis of cold-cast magnetic materials. The development of current sensors with core cast focused primarily on the possibility of their application for the measurement of large currents and for the purpose of measuring the electricity and power electronics. The article presents the results of measurements of transmission characteristics of the prototype sensor, the sensing ampli­fier design and measurement results of the entire scanning unit.

Transport critical current measurement of Y–Ba–Cu–O thin film fabricated by coating pyrolysis process

The coating pyrolysis or metal organic deposition process is expected to be an attractive method offering the possibility of cost reduction and ease of large-scale fabrication of YBCO thin films. This process could realize a high critical current density of YBCO thin films. However the critical current density was measured only by the induced current method. Therefore, we compared the results of the induced current method with those of the transport current method. According to the measurement results, these values were almost the same as 2 MA/cm 2, and a agreement between them was evident. The reaction between a YBCO film and indium contact and the change in quality of the YBCO film at the current contact point were examined. Because our experiments focused on large current applications such as the fault current limiter, reliable contact between the copper current lead and the YBCO film was essential. The difficulty of the large current measurement of the YBCO thin film was shown by our research.

Interrogation of a conventional current transformer by a fiber-optic interferometer

A new approach to the measurement of large currents at high potential is presented in which the output signal from a conventional current transformer is measured by transducing the voltage developed across the transformer secondary into phase modulation in a fiber-optic interferometer through a piezoelectric element. The demonstrated current range was 140 A, although the system is capable of measuring current as great as 3000 A. The current resolution is >10−1A/Hz over a frequency range of 30–104 Hz.

A low-cost multiple Hall probe current transducer

An inexpensive but highly stable and accurate transducer has been developed for the measurement of large currents associated with the operation of the DIII-D tokamak at General Atomics. The inherent problems with integrator circuits required by Rogowski loops and the excessive cost of ‘‘secondary compensation current’’ devices have led to this development. The transducer requires several inexpensive Hall effect devices and a simple, stable, and linear interface circuit. Analysis of the initial performance characteristics is very encouraging and has led to several useful applications of the transducer to date, with plans for the installation of additional devices in the future. The low cost and reasonable accuracy of the transducer make it an attractive alternative to commercially available devices.

A Direct-Current-Comparator Bridge for Measuring Shunts up to 20000 Amperes

A direct-current-comparator bridge for calibrating four-terminal resistors or shunts at currents up to 20 000 amperes is described. Measurements can be made at up to full rated current of the shunts so that the effects of the load coefficient are included. The resistor under test is compared with a reference resistor of higher value by measuring the ratio of the currents through the two resistors required to produce equal voltages across them. A comparator bridge with a range of 100 amperes and errors of less than 1 ppm has been described previously. Improvements to this bridge have been made, the main one being a reversing feature, which permits the currents through the resistors to be reversed in a few milliseconds. This makes an accurate measurement easier, particularly if there is a change of resistance due to heating. By connecting a second comparator in cascade, the range has been extended to 20 000 amperes at an overall ratio up to 2 × 106: 1, with only a slight loss of accuracy; the errors may be a few parts per million. Other applications of the measuring system are the accurate measurement of large currents or the calibration of transductors.

A resistor for the measurement of large direct currents

Serious uncertainties in the effective value of low resistances for the measurement of large currents may be caused by variations of current distribution at their terminals, due to the use of many conductors in parallel which are necessary for large currents or to variations in surface contact or pressure of clamping bolts. Temperature-rise is also an important cause of variation. The application of principles for the reduction of these errors has been the basis of the design of a resistor of 20 microhms, which has been found satisfactory as a reference standard for the measurement of currents up to 25000 amperes.