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In this study, a long‐distance non‐contact current measurement method is proposed based on the non‐contact sensor array measurement technology, combined with a new current algorithm. The sensor array is a vertical array composed of three three‐axis magnetic field (MF) sensors that is placed on the ground plane below the measured overhead line. The proposed current algorithm can optimize the geometry of the overhead line using the spatial MF values measured by the sensor array and then the three‐phase currents can be calculated. To improve the accuracy of current measurement, the spatial MF model in the algorithm considers the influence of cable sag. It enables a more accurate coupling matrix between the measured overhead line and the sensor array to be established. Additionally, the current algorithm architecture is designed using a composite algorithm to more optimally obtain the best three‐phase current values. A scale‐down overhead‐line measurement system is developed to test the proposed current measurement method. The results show whether a cable sag exists when the three‐phase currents are approximately balanced, with errors less than 2.0%. Moreover, it can be determined whether cable sag exists when the three‐phase currents are unbalanced, with less than 3.4% errors. [ABSTRACT FROM AUTHOR]

With the growing infrastructure for overhead lines, the demand for overhead‐line condition‐monitoring technologies has become increasingly urgent. Traditional current transformers used to measure three‐phase currents are bulky and difficult to install, which further increases the cost of monitoring. In order to meet the current state assessment needs of transmission and distribution networks, this study uses a novel magnetic‐field sensor array to realize nonintrusive overhead‐line current detection. Based on the magnetic fields measured by magnetic‐field sensors placed on the ground under the overhead line, the proposed algorithm can be used to calculate the three‐phase current values. The proposed method does not require on‐site calibration before the field measurements are conducted. With partially known overhead‐line geometry specifications from utilities, the algorithm can optimize the overhead‐line geometry and finally achieve accurate current detection. The simulation and experimental results verify that the proposed current‐detection technique can accurately calculate the three‐phase currents of the overhead line with only three three‐axis magnetic‐field sensors. [ABSTRACT FROM AUTHOR]

This paper presents scientific analyses of the wall paintings in Wudang Lamasery, which is located in the Baotou area of Inner Mongolia, China. Raman spectroscopy was used to analyze the pigments of the mural of the Lam rim Hall. The results show that vermilion, red lead, chrome yellow, emerald green and synthetic ultramarine were used. The existence of synthetic pigments provides a clue for the date the mural was painted. [ABSTRACT FROM AUTHOR]

An accurate and cost-effective islanding detection is in a great need for distributed generation (DG) integration. An onsite contactless islanding detection scheme is proposed in this article, based on a small number of tiny and portable electric field (EF) sensors. In contrast to the existing mainstream detection techniques, which are heavily depended on the instrument transformer measurement in substations, the proposed contactless scheme is able to be deployed on the ground below the overhead feeders, enabled by a compact EF sensor and the associated accurate frequency measurement algorithm. The effectiveness, robustness, efficiency, and security advantages of the proposed method are investigated and verified by the simulations using various feeder configurations. It is further supported by the laboratory experiments based on a scale-down overhead feeder testbed. [ABSTRACT FROM AUTHOR]

We propose a new contactless phase comparison method for high-voltage overhead lines. Combined with single-axis electric field (EF) sensing technologies, the new phase comparison method can perform a remote field measurement before the measured two overhead lines are interconnected. In the new phase comparison method, two single-axis EF sensor arrays are placed below the two measured overhead lines individually. A synchronous driver system wirelessly triggers the two EF sensor arrays synchronously to measure space electric fields. Then, two sets of measured electric fields are received by the synchronous driver system, and these data are used to carry out 1) positive/negative sequence evaluation and 2) phase evaluation. Finally, the proposed method can determine whether the three-phase voltage phases of the two overhead lines are identical. In addition, in order to ensure that the EF sensor arrays can synchronously measure electric fields, each EF sensor is designed with a built-in GPS device. Firstly, we simulated the electric field distribution of overhead lines using a finite element analysis (FEA) software, and then designed the placement of EF sensors on the ground. Finally, we validated the proposed method by experimental tests on a reduced scale model of overhead lines. [ABSTRACT FROM AUTHOR]

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. [ABSTRACT FROM AUTHOR]

Measuring the current in high-voltage direct current (HVDC) systems is always regarded as a challenging task. For transmission systems, dc current transformers or sensors are only available in substations and converter stations. In order to provide more flexibility and convenience, this paper proposes a contactless dc current sensor, which can be easily placed on-site in the environment of HVDC overhead transmission lines. The proposed method significantly improves the convenience and safety of the HVDC current measurement. Using a magnetic-field sensor array, the proposed current algorithm can optimally calculate the overhead-line currents with partially known overhead-line geometry. The simulation results in this paper demonstrate that the proposed method can accurately calculate the HVDC current. Moreover, the proposed method is validated by a reduced-scale HVDC overhead transmission line. [ABSTRACT FROM PUBLISHER]

Most traditional voltage transformers in transmission and distribution networks are installed inside the substations. Nearly no accessible voltage information in the real‐time scale is available for field engineers to carry out the field measurement for the purposes of the power quality inspection and the equipment maintenance. In order to offer an on‐site and easy‐to‐use solution for the field measurement, the authors propose a novel electric‐field (EF) sensor array based technique for measuring the overhead‐line voltage. Based on the EFs measured by the EF sensor array and the partially known overhead‐line geometry information from utilities, the proposed voltage algorithm can accurately calculate each‐phase voltage without an on‐site calibration before conducting the field measurement. The simulation results demonstrate that the authors' proposed technique with only three EF sensors can accurately calculate the overhead‐line voltages and successfully reconstruct the real‐time three‐phase waveforms. The experiment results verify the feasibility of the proposed voltage sensor for the overhead‐line voltage measurement. [ABSTRACT FROM AUTHOR]

How to measure ac currents in a bundle of inaccessible, enclosed conductors has been a challenging problem but with many potential applications. This paper presents a method to solve the problem using an array of magnetic field sensors. The proposed method consists of two novel ideas. The first idea is to use an off-site calibration method to establish sensor parameters including sensing position and angle, which provides more accurate sensor parameter estimation than their nominal values. The second idea is to “measure” (i.e., calculate) conductor currents and positions based on the sensed magnetic fields and preestablished sensor parameters. This process is simplified since the sensor information is obtained by the first idea. Both calibration and measurement tasks are formulated as nonlinear least square problems and solved efficiently. The proposed method is demonstrated for the cases involving ideal three-conductor system and practical residential service cable enclosed in a plastic conduit. The method has the potential for contactless current measurement of Romex cables and overhead distribution lines. [ABSTRACT FROM PUBLISHER]

Owing to increased capabilities of power quality monitors, synchronized harmonic phasor data are becoming more widely available. Taking advantage of the new data, this paper presents a new and effective method to solve the problem of how to estimate the harmonic impact of several individual loads on the harmonic voltages at a specific location of a power network. The method uses the independent fluctuation of the harmonic sources and is solved as a blind source separation problem. The proposed method has been verified through simulation verification where harmonic currents measured at actual substations are used as input so realistic load fluctuations are considered. Furthermore, lab experiments are conducted to validate the proposed method. [ABSTRACT FROM AUTHOR]

Overhead and underground power line monitoring is an essential infrastructure for advanced operation in the smart grid. Wireless sensor networks are attractive to remote power line monitoring, due to their rare geography restrictions, simple engineering design, and flexible equipment expansion. Considering the ZigBee’s characteristic of low transmission rate, almost commercial sensors adopt the high-speed communication, such as Cellular and WiFi, to implement the real-time wireless monitoring. However, among all wireless technologies, ZigBee, characterizing high security, ultra-low power consumption, reliable network, low cost, and ease of design, is widely used in many industries. This paper proposes a new ZigBee-based communication for multifunctional electronic current transformers (ECTs), which are used in overhead and underground line monitoring. To tackle ZigBee’s low transmission rate, the proposed method involving a transmission strategy can make the ZigBee-based communication satisfy both measurable and protective purposes of multifunctional ECTs. Finally, the new ZigBee-based wireless communication is implemented and integrated with an ECT, which is based on the coreless Hall-effect current transformer (HCT), and the proposed ZigBee-based wireless multifunctional HCT is called ZiHCT. The measurement results show that the ZiHCT can achieve accuracy not only to Class 0.5 for measuring CTs, but also to Class 5P20 for protective CTs according to IEC standard 60044-8. [ABSTRACT FROM PUBLISHER]

Compared with traditional current transformers (CTs), electronic current transformers (ECTs) are characterized by small volume, light weight, good isolation, good linearity, and easy digitization. Hence, ECTs are one of the primary devices for signal digitization for supervising intelligent substations. We design a coreless ECT using Hall sensors as well as its mechanism and circuit configuration in order to replace traditional CTs and other CTs. The proposed ECT achieves Class 0.5 accuracy for measuring CTs and accuracy Class 5P21 for protective CTs according to IEC Standard 60044-8. An additional power supply is required to drive the ECT. Considering that there are no usable power supplies for special measurement environments, we use the surrounding magnetic fields induced by the cable currents as the power supply. A self-contained power supply is proposed and integrated with a backup battery power supply and a battery protection circuit to ensure that power is supplied for different operating conditions. In addition, we design a protective device to protect the back-end circuits of the self-contained power supply in case of a fault occurring in the power system. [ABSTRACT FROM PUBLISHER]

This paper presents a multifunctional coreless current transformer based on the Hall effect (multifunctional HCT), and designs its actual electronic circuit that can discriminate load and fault currents to perform both metering and protective functions. The multifunctional HCT has two primary circuits: 1) distinguishes the load current from the fault current and 2) delivers the current value using an analog multiplexer. This HCT can eliminate the 2.5\pm 0.05~V offset voltage of commercial Hall sensors. It possesses two amplifiers with different gains. Therefore, this multifunctional HCT accurately measures power currents during the operations in measurement systems and protection systems. Using a low-pass filter, the multifunctional HCT is not only capable of reducing noise interference, but also improves the accuracy of power current measurements. The experimental results show that the multifunctional HCT can exhibit an accuracy class of 0.5 for both the measurement and protection of power systems within IEC standard 60044–8. Because the proposed multifunctional HCT does not have core and saturation problems, the accuracy class and limit can achieve the standard accuracy limit factor grade of 63. [ABSTRACT FROM PUBLISHER]

Based upon the analysis of load signatures, this paper presents a nonintrusive load monitoring (NILM) technique. With a characterizing response associated with a transient energy signature, a reliable and accurate recognition result can be obtained. In this paper, artificial neural networks, in combination with turn-on transient energy analysis, are used to improve recognition accuracy and computational speed of NILM results. To minimize the distortion phenomenon in current measurements from the hysteresis of traditional current transformer (CT) iron cores, a coreless Hall CT is adopted to accurately detect nonsinusoidal waves to improve NILM accuracy. The experimental results indicate that the incorporation of turn-on transient energy algorithm into NILM significantly improve the recognition accuracy and the computational speed. [ABSTRACT FROM AUTHOR]

Current transformers (CTs) are used to measure line currents in a power network for indicative and protective purposes. However, due to magnetic hysteresis in the cores, traditional CTs may saturate when they detect large fault currents. Thus, a more efficient and accurate device is required. This paper aims at designing a more economical device, a microsensor to measure power network currents. The characteristics of this new design are measured and discussed. The new component will not be saturated for fault currents as high as 40 kA and can be used directly with an intelligent protective system or a digital meter for smart metering of electric power networks if it is designed with an integrated circuit (IC) chip. [ABSTRACT FROM PUBLISHER]

A new method for performing power current measurement is proposed; this method involves the use of Hall sensors without iron cores. A new apparatus for implementing this method, called coreless Hall-effect current transformer (HCT), has been developed. The HCT consists of four Hall sensors connected to a weighted adder. Four Hall sensors are symmetrically attached to an electric conducting cable, and the output of the sensors is connected to the weighted adder. The weighted adder performs the “average” operation, thereby obtaining the average voltage. Since the average Hall voltage is obtained, the HCT can eliminate the ambient interference. A measurement framework is designed and implemented to compare a series of waveforms obtained by HCTs with those measured by traditional current transformers (CTs) and linear CTs. Current measurement results show that an HCT can measure current with greater accuracy than traditional CTs. Moreover, in the presence of faults, HCTs do not encounter problems related to saturation that exist in traditional CTs. [ABSTRACT FROM AUTHOR]