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Fiber optic current transformers (FOCTs) have advantages over conventional current transformers. However, the application of FOCTs is significantly limited by the birefringence effect caused by temperature and vibration. Thus, this study proposed a sensing scheme of coupling a fiber polarization rotator to improve the robustness of FOCTs. First, the mathematical model of the proposed FOCT was derived using the Jones matrix, and the error caused by the birefringence effect was computed. Then, the FOCT was modeled by applying the finite element method to verify the effectiveness of the proposed FOCT in improving the temperature and vibration robustness. Finally, experiments were conducted, including temperature, vibration, and frequency response characteristics. The proposed scheme was compared with the basic polarimetric detection (PD) scheme and several state-of-the-art schemes. Results show that the maximum error of the proposed scheme is 1.7% in the temperature range from $- 20 ^{\circ }\text{C}$ to $80 ^{\circ }\text{C}$ (that of the basic PD scheme ranges from −7.05% to 9.75%). In the vibration test, the maximum output error of the proposed scheme is 0.72%, while that of the basic PD scheme reaches 4.89%. Meanwhile, the proposed FOCT meets the requirements of the measurement of high-amplitude and high-frequency transient currents, such as lightning impulse current, in power systems. [ABSTRACT FROM AUTHOR]

Localization of partial discharge (PD) is a reliable and necessary technique for early prediction of impending failure in transformer windings. Different PD sources have diverse impacts on insulation, and PDs measured at different locations exhibit unique energy characteristics. An approach based on the energy characteristics of the PD signal is proposed here to locate PD inside the winding. An electrical detection method has been considered with PD pulses measured at the top and bottom of the winding through high-frequency current transformers (HFCTs). To reveal multiscale intrinsic characteristics of the PD signal, authors extracted intrinsic mode function (IMF) using ensemble empirical mode decomposition (EEMD). Next, the instantaneous energy distribution-permutation entropy (PE-IED) values of the first several IMFs were calculated to capture the energy of the PD. Then, dimensionality reduction was ensured by the fast principal component analysis that uses the fixed-point algorithm method. Finally, adaptive density-based clustering using the nearest neighbor graph (ADBSCAN-NNG) approach is proposed to identify the local high-density energy components. The proposed method is verified using the winding of a vacuum cast coil transformer and the localization results reveal the feasibility of the proposed method in locating PDs over existing localization algorithms. The reduced complexity of the proposed algorithm ensures the accurate onsite PD localization in transformer windings. [ABSTRACT FROM AUTHOR]

The measurement of harmonics is one of the key tasks in modern power systems, performed basically for power quality assessment, verification of planning levels compliance, immunity and compatibility purposes, and so on. Especially at medium voltage (MV) and high voltage (HV) levels, harmonics are always measured through voltage and current transformers (VTs and CTs), which very often are inductive. Recent articles show that inductive VTs and CTs, due to the intrinsic iron core nonlinearity, can introduce errors up to some percent in harmonic measurements. This article aims to investigate in-depth this phenomenon by analyzing how the accuracy of harmonic measurements performed through an inductive MV VT is affected by the presence subharmonics in its input voltage. Subharmonics are spectral components having frequencies lower than the power frequency, that is 50 Hz for European countries. Some theoretical considerations are carried out and the performances of two different inductive MV VTs are tested in various operating conditions. Experimental results show that subharmonics can worsen the harmonic measurements done through inductive VTs up to some tens of percent. [ABSTRACT FROM AUTHOR]

This article presents a new method for effective detection of ac series arc fault (AF) (SAF) and extraction of SAF characteristics in residential buildings, which addresses the challenges with conventional current detection methods in discriminating arcing and nonarcing current due to their similarity. Different from the traditional method, in the proposed method, the differential magnetic flux is coupled to obtain high-frequency signals by putting the live line and the neutral line through the current transformer, which can effectively solve the problem of SAF features disappearing in the trunk-line current. However, similar to the traditional method, the effectiveness of the proposed coupling method could also be compromised when being used in cases with dimmer load and load starting process. This is found to be caused by the presence of high-amplitude pulse phenomenon in the nonarcing signals in these scenarios, which are incorrectly detected as arcing signals in other loads. To address this issue, a short-observation-window singular value decomposition and reconstruction algorithm (SOW-SVDR) is used to enhance the capability to identify SAFs by the coupling method. The proposed method has been implemented and validated according to the UL1699 standard with different types of loads connected to the system and also tested under their starting processes. The experimental results show that the proposed approach is more effective in detecting AFs compared with existing methods. [ABSTRACT FROM AUTHOR]

A sampling current ratio measurement system has been developed to calibrate the voltage dependence of ratio error and phase displacement of current transformers (CTs) used for medium-voltage (MV) and high-voltage (HV) applications. The influence of voltage-induced leakage current on the apparent ratio error and phase displacement of the reference circuit was unambiguously demonstrated using a novel measurement method. Measurement results for voltages up to 24 kV show that the observed leakage current is purely capacitive and caused by the shielded cable capacitance of the HV cable used to feed the current. The maximum ratio error and phase displacement were found to be about 100 parts in 106 and $100~\mu $ rad for the smallest current of 100 A used for these investigations. Since these values scale linearly with the applied voltage and inversely proportional with current, the assumption of negligible voltage dependence used in other reference systems presented in literature is questionable. Using the corrected reference circuit, a commercial class 0.2S MV CT with 2500-A nominal current was calibrated at voltage levels up to 24 kV. The voltage dependence of ratio error and phase displacement for primary currents up to 500 A was demonstrated to be capacitive as well, with a maximum impact on the current ratio of almost 0.9% for a primary current of 100 A (corresponding to 3.6% at 1% of nominal current). This value is beyond the limits of in-force standards, which emphasizes the necessity of implementing voltage dependence testing in those standards. [ABSTRACT FROM AUTHOR]

A reference setup for system calibration of industrial transformer loss measurement (TLM) systems consists of three main components, a voltage divider, a current transformer, and a power meter, and their phase displacements should each not be more than 10 $\mathrm {\mu }$ rad to achieve an overall system uncertainty of better than 20 $\mathrm {\mu }\text{W}$ /VA. We have extensively verified the uncertainty level of the current-comparator-based capacitive voltage divider (CVD) used in the TLM reference setup of the Van Swinden Laboratorium (VSL), both from the component level and the system as a whole. Different practical conditions relevant for on-site measurements are considered, e.g., measurement cable lengths, cable types, and grounding. The verification measurement results show an agreement of better than $(6 \pm 6) \times 10^{-6}$ in ratio error and $(4 \pm 6)~\mathrm {\mu }$ rad in phase displacement between the CVD component and system calibrations up to 100 kV. Requirements for achieving this agreement are adequate grounding of the CVD and the use of triax cable between the high-voltage (HV) capacitor and the CVD low-voltage electronics in case large distances have to be covered on-site. The $(4 \pm 6)~\mathrm {\mu }$ rad agreement in phase displacement is well within the required 10 $\mathrm {\mu }$ rad limit for voltage measurements as part of on-site TLM system calibrations with 20 $\mathrm {\mu }\text{W}$ /VA overall uncertainty at low power factors. [ABSTRACT FROM AUTHOR]

This article shows the design of a simple construction two-stage current transformer with ratios from 5 A:5 A to 2000 A:5 A. It can be self-calibrated. Primary windings are separated into sectors to allow series–parallel configurations. Beginning with 5 A:5 A-ratio self-calibration, the higher ranges relate their errors to this first one, considering parasitic effects. Stray capacitances are considered as the major source of error when changing the configuration of the primary winding. New methods to calculate and compensate them are proposed, and electronic devices are used to reduce ratio error and phase displacement to few $\mu \text{A}$ /A and $\mu $ rad. The participation of this transformer as the UTE standard in an international comparison confirmed the calculated performance. [ABSTRACT FROM AUTHOR]

The inherent advantages of fiber optical current transformer (FOCT) are very attractive for high-voltage applications when compared with conventional transformers. However, the accuracy and long-term reliability of FOCT can be greatly affected by temperature. Fiber temperature sensors are suitable for FOCT temperature compensation, especially in ultrahigh voltage (UHV) applications. As a result, a fiber temperature-sensing scheme based on the temperature birefringence effect of polarization maintaining fiber (PMF-TS) was proposed. A high integration real-time temperature correction FOCT based on PMF-TS (PMFTS-FOCT) was designed, and a prototype with rated current of 5000 A and rated voltage of 1100 kV was developed. The accuracy, temperature, frequency response, step response, and transient response of the system was tested. The results showed that within the temperature range of −40 °C to 70 °C, the ratio error (RE) of 500–5500 A was less than ±0.2% after temperature correction, and in the frequency range of 50–1200 Hz, RE and phase error (PE) were less than ±0.75% and $110~\mu \text{s}$ , respectively. The step response time was less than $125~\mu \text{s}$ , the overshoot was less than 1.5%, and the composite error was 0.807% for the 50 000-A transient current. We proved that PMFTS-FOCT had good steady-state and transient performance and the possibility for measuring dc and ac harmonics, whose performance meets the error limit requirements specified in GB/T 26216.1-2010. [ABSTRACT FROM AUTHOR]

Reliability of power distribution network is highly desired by end customers. The power utility companies make best efforts to ensure balanced power transfer for single-phase customers. Phase unbalancing is common in congested power distribution systems where a large number of single-phase consumers are served by three-phase transformers. It deteriorates transformer efficiency and results in increased power system losses. As a standard practice, utility providers use portable CTs to periodically measure phase currents to reduce the unbalanced loading of transformers. The approach requires manual intervention and regular inspections. This article proposes a novel noncontact method for the measurement of unbalanced single-phase loading using a single magnetic sensor and processing with a trained neural network (NN). This article employs variation in phase and magnitude of the magnetic field produced by three-phase line conductors to detect and identify the unbalanced lines. The optimal sensing location is determined by using outcomes of coherence between the training and test data. Then, a trained NN uses a pattern recognition algorithm to estimate the unbalanced and the balanced loading. The method is comprehensively tested by numerical simulations and experimentation, which involves various potential configurations of distribution lines (flat, vertical, and delta). The method of estimation of unbalanced loading by magnetic field sensing and pattern recognition method has been experimentally implemented and verified in the laboratory setup. The results provide accurate unbalance phase detection with an error of less than 1%. [ABSTRACT FROM AUTHOR]

This article presents a study on low-power passive current transformers. In particular, the performance of three Rogowski coils has been assessed when multiple influence quantities were acting on them: conductor position, frequency, and ambient temperature. First of all, their single effects have been assessed, then all their possible combinations have been tested. From the results, it can be concluded that the ratio error is mostly affected by the combination of uncentered positions and temperatures applied to Rogowski coils. Contrastingly, the phase error is substantially not influenced by any quantity. Therefore, the proposed set of tests could become a benchmark in Rogowski coil testing. [ABSTRACT FROM AUTHOR]

Fault classification of power distribution cables is essential for tripping relays, pinpointing fault location, and repairing failures of a distribution network in the power system. However, existing fault-classification techniques are not totally satisfactory because they may: 1) require the precalibration of responding threshold for each network; 2) fail to identify the three-phase short-circuit faults. since some electrical parameters (e.g., phase angle) are still symmetrical even in abnormal status; and 3) be invulnerable of electromagnetic interferences. In this paper, a fault-classification technique by detecting decaying dc components of currents in faulted phases through magnetic sensing is proposed to overcome the shortcomings mentioned above. First, the three-phase currents are reconstructed by magnetic sensing with a stochastic optimization algorithm, which avoids the waveform distortion in the measurement by current transformers that incurred by the dc bias. Then, the dc component is extracted by mathematical morphology (MM) in phase currents to identify the fault type together with the polarity of dc components. This method was verified successfully for various fault types on a 22-kV power distribution cable in simulation and also a scaled power distribution network experimentally. The proposed method can enhance the reliability of the power distribution network and contribute to smart grid development. [ABSTRACT FROM AUTHOR]

We present in this paper a method and apparatus for nonintrusive measurement of active energy in low-voltage ac installations. In the proposed method, the active power is calculated from the voltage and current waveforms, and the phase shift between them. No voltage amplitude measurement is required since the nominal voltage of the ac installation is considered as the actual voltage. This approach bypasses the main disadvantage of capacitive ac voltage probing: low accuracy in amplitude measurements due to variations on the sensor coupling capacitance. The energy meter that implements the technique is composed of a commercial nonintrusive current sensor (clamp-on current transformer) and a contactless capacitive voltage sensor—designed to measure the voltage phase and waveform. The voltage sensor includes a shield to isolate it from external electric fields, making the energy meter suitable for applications in polyphase systems. The developed energy meter does not require on-site calibration, galvanic contact to the phase conductors, neither electrical circuit opening, allowing for quick, safe, and easy installation on overhead service drop line. Due to these characteristics, it can be used by electricity distribution companies in the preinspection of consumer units suspected of fraud. Experimental results proved that the developed energy meter is insensitive to the characteristics of cables (width and insulation), external electrical fields, as well as to the voltage sensor capacitance variations. The error of the active energy measurement under real condition in a two-phase installation was 1%. [ABSTRACT FROM AUTHOR]

Insulated power cables are becoming increasingly popular in today’s developing distribution and transportion networks. However, due to aging, deterioration, and various operational and environmental stresses, insulation defects may appear and so the cable needs to be monitored in a timely manner to avoid unexpected failures. Many of these defects are responsible for partial discharge (PD) activity. The localization of the sources of these discharges is a highly decisive facet in the condition-based monitoring of power cables. The techniques for the localization of single-PD defects in insulated power cables are well presented in the current bibliography. However, when several simultaneous PD sources are active, the localization of the sources becomes quite complex. This paper develops an efficient technique for the separation and localization of multiple PD sources in a medium voltage cable. The experimental results are obtained with single-end-based measurements using a high-frequency current transformer in a laboratory environment. The data processing based on the spectral characteristics of the signals is carried out by using the power ratios technique in order to determine the presence of different types of PD. Once the signals are separated, the PD sources can be localized with an individualized analysis of each source through time-domain reflectometry. The proposed methodology can be very valuable to improve the location diagnostic capability of the condition-based monitoring solutions, especially for underground cables. [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]

With the proliferation of harmonic sources in power systems, current transformers (CTs), which are the most widely used current transducers in power systems, will have to measure and monitor signals with increasing levels of distortion. The accuracy of the measurement can be affected by the nonlinear response of the CT, which is dependent on the distortion in the measured signal, but nonlinear mathematical models can be used to compensate the measured value. In this paper, the complex ratio of the CT is modeled using a frequency domain model based on tensor linearization, obtaining a real-valued compensation matrix. An accurate measurement setup has been built to characterize the CTs performance in distorted conditions. Experimental results using the proposed compensation technique are presented and discussed for two commercial CTs of accuracy class 0.5 and 1. It is demonstrated that the proposed technique can accurately reconstruct the harmonic components (up to several kilohertz) of the CT primary current from the measured CT distorted secondary current. [ABSTRACT FROM AUTHOR]

Current transformers (CTs) are extensively used for the measurement of electrical energy, and hence they play a crucial role in the revenue generation for power distribution utilities. The novelty of this paper is that it presents artificial neural network (ANN) application for the ratio and phase angle error corrections of CTs in the presence of harmonic distortions. In this paper, the behaviors of silicon iron alloy and nanocrystalline alloy CTs are examined by the means of a number of experimental tests under the sinusoidal and distorted waveform conditions. The relation between the nature of CTs secondary current waveforms (CTSwf) with their metrological properties, connected burdens, and nature of load currents (linear or nonlinear) is established. The training data are obtained by the nature of CTSwf in terms of amplitude errors, time shifts, and deviations caused by different harmonic contents between input and output quantities. The ANN is trained for various operating conditions. The implementation of the error correction system and data acquisition is done using dSPACE 1104 software. The experimental results illustrate that the proposed technique can be used for error compensation in case of sinusoidal and the distorted waveform composed of fundamental and many harmonics. [ABSTRACT FROM AUTHOR]

Current transformers for ac power systems applications are usually calibrated by applying sinusoidal currents at different frequencies. The main limitation of this approach is that it does not take into account nonlinearities that may have a significant impact on harmonic current measurement. A more accurate characterization should be based on test currents that are similar to those found in normal working conditions. However, this demands a proper current generator able to generate multitone waveforms with proper accuracy, which is seldom available in laboratories. This paper proposes a simple approach to implement a current generator, based on a waveform generator, a power amplifier, and a transformer which allows boosting the output current capability. Its uneven input–output response can be compensated through linear prefiltering of the desired current waveform. When the generator is employed to reproduce a specific class of current waveforms, such as those typically found in ac distribution grids, an optimal compensation filter can be easily designed. This approach allows canceling systematic nonlinearities introduced by the transformer and the power amplifier, thus significantly increasing accuracy with respect to a conventional frequency response compensation, as confirmed by experimental results. [ABSTRACT FROM AUTHOR]

An overview of the development and performance of a special high precision multi-ratio three-stage CT and its application for loss measurements of EHV three-phase shunt reactors with test voltages up to a phase voltage of 1100 kV at Royal SMIT Transformers are presented and discussed. It features current ratios of 500 A/1 A, 400 A/1 A, 300 A/1 A, 200 A/1 A, and 100 A/1 A with ratio errors within $3 \times 10 ^{-6}$ in both magnitude and phase with burdens up to $1.0~\Omega $ and at power frequencies of 50–60 Hz. [ABSTRACT FROM AUTHOR]

This paper deals with the accuracy evaluation of a method for gathering synchronized phasor measurements of electrical quantities in nodes of power networks. Usually, this task is performed using commercially available instrumentation, for instance, the phasor measurement unit. They rely on a common time reference signal provided usually by the GPS system. After a brief recall of two methods already presented by authors in previous papers, which do not require a common time reference for providing synchronized phasors of voltages at the network nodes, the major sources of uncertainty in the measurement chain (lengths of the branches of the network; per-unit length reactance of the cables; and effect of the instrument transformers) are considered and investigation on their contribution, in one of the two methods, to the overall uncertainty performed. [ABSTRACT FROM AUTHOR]

As the dedicated equipment in electricity measurement, high-accuracy metering is an essential feature of the electronic power meter. In actual measurement, various factors will affect the metering accuracy of energy metering system. Among them, the phase shift introduced by the current transformer is an important cause for the measurement error, especially in the case of a light load. The existence of this phenomenon will directly affect the fairness and justice of all the commercial transactions in the energy market. With regard to this matter, an effective digital calibration algorithm based on piecewise Lagrange interpolation for reducing phase shift of static meters is presented in this paper. Moreover, an analytical expression for the absolute error of the proposed algorithm is derived. The proposed method is advantageous, since it is simple, efficient, and is of high accuracy. The experimental tests have been performed to verify the effectiveness and feasibility of our calibration method. [ABSTRACT FROM AUTHOR]

An efficient system for the compensation of current transformers over a wide frequency range is presented. The proposed technique is based on digital signal processing and inverse modeling using the frequency domain approach and Wiener filtering. Since the proposed technique applies finite impulse response filtering, the compensation filter is absolutely stable. The modeling error is reduced using a small time delay in the modeled inverse transfer function, which is unobservable for the human operator. The proposed algorithm is implemented in real time using a PCI eXtensions for Instrumentation system. [ABSTRACT FROM PUBLISHER]

In recent years, test sets for both conventional and analog nonconventional instrument transformers have been made commercially available. Reference transformers are still of the conventional type. Therefore, test sets need to compare an analog signal of a conventional level with another analog signal of a different order of magnitude or, in the case of current-to-voltage transformers, even a different quantity. Traditional designs based on bridge techniques are not suitable for this application. This paper describes a new calibrator that reaches uncertainties of the order of 10 × 10−6 while being suitable for the calibration of test sets for nonconventional analog instrument transformers and fully computer-controlled. [ABSTRACT FROM AUTHOR]

A comparison of two systems based on different methods for calibration of current transformers at several different transformation ratios, burdens, and power frequencies of 60 Hz and 50 Hz is performed at the National Research Council of Canada. The obtained discrepancies in ratio and phase errors are within 5 μA/A and μrad, respectively, for small test currents and less for larger test currents. [ABSTRACT FROM AUTHOR]

Overhead high-voltage transmission lines (HVTLs) extend over diverse geographic regions under uneven weather conditions, where sag and wind-induced conductor motion poses serious issues for uninterrupted power distribution by HVTLs. Sag reduces the ground clearance of the line, whereas conductor motion may result in phase to phase short circuit, and damage to support structure. A real-time estimate of these factors is deemed important to develop requisite prevention measures. In this paper, we present a novel method to cater for sag and motion estimation in real-world scenarios. Our method can detect a change in sag and conductor motion, whether it is symmetrical or unsymmetrical to one or more conductors. We require uniaxial magnetic-field (MF) sensors mounted at support tower, equal to conductors, and synchronized with current-transformer (CT) data at substation. The sensors provide noncontact MF measurements, which are time stamped and transmitted to the substation. The data are then simultaneously processed along with electric current readings from the CT. For processing, we developed a unified algorithm that first distinguishes variation in sag from motion in conductor. Then, it estimates the corresponding sag or motion in any of the conductors. The method is verified first by numerical simulations, and then with a scaled setup in laboratory. Different test cases were identified by the algorithm. Error remains $\leq 1$ % for unsymmetrical sag estimation. In addition, trajectory of a conductor in motion is retrieved. Where the root mean square error between actual and retrieved conductor amplitude was only 0.0833 for the observation window of 200 ms. [ABSTRACT FROM PUBLISHER]

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 10^6 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. [ABSTRACT FROM PUBLISHER]

This paper describes a development framework for alternating current ratio standard working at high audio frequencies. To realize this, first, a calibration method for frequency-dependent balancing current generators (BCGs) producing error currents to balance current comparators (CCs) is proposed. Second, the BCG error correction is made not only for the current transformer (CT) calibration but also for the CC self-calibration. Third, practical capacitive error corrections are also proposed to be introduced for the CT and CC calibrations. Finally, in consideration of the BCG error, capacitive error, and compensated CC error, a proposed way of calculating CT error and estimating its uncertainty is described. [ABSTRACT FROM PUBLISHER]

Modern commercial dc current transformers (DCCTs) can measure currents up to the kiloampere range with accuracies better than 1 \times 10^-5 . We discuss here a DCCT calibration method and its implementation with commercial instruments typically employed in low-resistance calibration laboratories. The primary current ranges up to 2 kA; in the current range <100 A, the calibration uncertainty is better than 3 \times 10^-7 . An example of calibration of a high-performance DCCT specified for primary currents measurement up to 900 A is discussed in detail. [ABSTRACT FROM PUBLISHER]

In this paper, the measuring and calibration techniques useful for ensuring the traceability of nonconventional voltage transformer (VT), used in ac power plant up to 52 kV, are described and discussed. In particular, a setup made by commercially available devices is presented and an in-depth accuracy analysis is performed by considering all the uncertainty sources located in the measurement chain. The obtained results prove that it can be used for the calibration of 0.5 accuracy class low-power VTs. In addition, the sources that contribute more to the uncertainties on the ratio and phase errors are highlighted and suggestions on where to act to further improve the accuracy of the presented setup are given. [ABSTRACT FROM AUTHOR]

The development and testing results of a new current transformer (CT) test set at Physikalisch-Technische Bundesanstalt are described. The operation range for the ratio based bridge is intended for frequencies from 16.7 Hz up to 20 kHz. Equal setups of magnetically shielded current comparators with primary windings for rated currents from 100 mA up to 5 A convert the secondary currents of the standard CT and of the transformer under test (TUT) into proportional voltages. The errors of the TUT are calculated from the subsequent measurement of the complex voltage ratio. This current bridge and the voltage-ratio-based method allow comparing CTs with nonequal ratios. At 50 Hz, the measuring system offers an extended measurement uncertainty of less than 2 ppm or \(\mu \) rad, respectively. The bridge is verified for use with uncertainties of below 200 ppm or 400 \(\mu \) rad at a frequency of 20 kHz. [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]

This paper presents a novel coreless current sensor unit for measuring electrical current of circular conductors. The proposed sensor unit consists of three magnetic field sensors and a microcontroller unit (MCU). The new sensor unit does not need a bulky magnetic core necessary for magnetic field concentration, and can be used in the same way as conventional current transformers (CTs). An algorithm is developed to calibrate the outputs of the magnetic field sensors (e.g., Hall effect integrated circuits (ICs) with respect to the relative position of the current-carrying circular conductor. The algorithm can be implemented on a low-cost MCU for automatic real-time operation. Unlike other coreless magnetic field sensors that need to be fixed onto the conductor for accurate current measurement, the proposed sensor unit affords a more flexible installation option. A hardware prototype is constructed for the proposed coreless current sensor unit. The performance evaluation results show that the accuracy of the proposed sensor unit is comparable to the conventional magnetic core CTs. [ABSTRACT FROM PUBLISHER]

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 \muA/A in magnitude and 0.8 \murad 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 \muA/A in magnitude and 0.5 \murad in phase. [ABSTRACT FROM PUBLISHER]

This paper describes a new method for determining phase angle errors of shunts with rated currents at 50 and 100 A at frequencies from 25 to 100 kHz. The method is based on the use of a three-branch binary inductive current divider to measure the phase angle errors of high current shunts against a phase angle reference standard with only one step. An inductive high current shunt has been designed using a 100:1 current transformer connected in parallel with a 1-\Omega shunt. The phase angle errors of resistive high current shunts and the inductive high current shunt have been measured. The level dependence in phase angle errors of three different types of high current shunts has been evaluated at currents from 1 to 100 A. The measurement results and standard uncertainties of the phase angle errors of high current shunts are reported. [ABSTRACT FROM PUBLISHER]

The understanding of high-current events such as short-circuit transients and impulse currents is important for power quality management. The work carried out and presented in this paper is focused on the characterization of commercial current transducers for traceable on-site measurements of 8/20 \mu \s (rise/fall time) impulse currents up to 50 kA peak value with a target uncertainty of 0.1% for the complete measurement system. The investigation method consists of using two current transducers based on different technologies that will detect simultaneously the same impulse current. [ABSTRACT FROM PUBLISHER]

This paper presents two methods for determining the ratio error and the phase displacement of a protective current transformer (PCT) with a transformation ratio of 10 kA/1 A and a measuring current transformer (MCT) with a transformation ratio of 20 kA/5 A. The primary conductor passed by a current (10 or 20 kA) placed in the center of the toroid is replaced by a current loop with ten turns placed in the center of the toroid. In the second case, the conductor is replaced by ten turns uniformly distributed along the circumference of the toroid. The primary current (2 or 1 kA) is measured in both cases using a toroidal current comparator, and the secondary current difference is evaluated by means of a current transformer (CT) error measurement system. The errors were also measured using a CT analyzer. [ABSTRACT FROM PUBLISHER]

Current measurement is required to ensure the correct operation of power systems. Conventional current transformers are still widely employed in such networks, but their well-known limits make them not suitable for the incoming smart meters. In this paper, a current sensor based on proper measurements of the magnetic field produced by the primary current is proposed. Its main feature is the capability, owing to its particular geometry, of neglecting the effect of external fields without using traditional coil structure. An experimental analysis of its performance in both time and frequency domains is presented and discussed. [ABSTRACT FROM PUBLISHER]

To equivalently and effectively test the shielding effect of a heavy current transformer (HCT) with shielding coils in a laboratory, an eccentric bus-bar testing method has been used to simultaneously simulate the effect of primary bus bar and adjacent bus bar since 1970s. However, there has not yet been an effective way to determine the crucial parameters, particularly the eccentric distance, which means the distance from the center of an eccentric bus bar to the center of an HCT. This paper presents several analytical formulas to determine the eccentric distance and relevant parameters in the testing method, which may overcome the difficulty at present. The formulas are derived out from a magnetic circuit model and further verified by a finite-element method. Numerical results show that these formulas are effective and easy to use in the testing of an HCT. Most importantly, the source of an equivalent relative error has been also investigated in detail. Furthermore, if the eccentric current, which should be equal to the original primary current, is still too high to be reproduced in a laboratory, auxiliary and compensating windings could be adopted to reduce it. [ABSTRACT FROM PUBLISHER]

The development of a computer-controlled current-comparator-based calibration system to determine the current ratio errors of high-voltage conventional and nonconventional current transformers (CTs) under actual operating conditions of high-voltage and distorted current waveforms up to 100 kV and 2000 A is described. The ratio errors of a CT are affected by the applied high voltage due to capacitive currents flowing in its winding. The errors are also affected by the phase angle of the primary currents with respect to the operating high voltage. Therefore, the new calibration system allows the phase angle of the test primary currents to be adjusted at power factors of zero lag through unity to zero lead. The uncertainty k = 2 of the new calibration system is estimated to be not more than 20 \times 10^-6 for both the in-phase and quadrature components of the measured ratio errors. [ABSTRACT FROM AUTHOR]

The objective of this paper is to present a simple sensor based on Faraday's Law together with an integration and amplifying stage and used this for measuring fast current pulses. Its behavior in time and frequency is tested by measuring Partial Discharges (PD) in electric insulation systems following the guidelines given in the standard IEC 60270. The measurements are also taken with two other sensors, a commercial high frequency current transformer and a resistive transducer, with the aim of comparing the results obtained with the proposed probe and obtaining an estimation of its sensitivity. An estimation of the uncertainty of the measurements is also calculated obtaining an error similar to other commercial devices. [ABSTRACT FROM AUTHOR]

So far, there has not been any method that is both effective and accurate enough to test the performance of a heavy current transformer (HCT) under electromagnetic interference from adjacent bus-bars since the primary and adjacent currents are too high to reproduce in a laboratory. A new testing method termed as the “multiple-coil testing method” is presented in this paper to overcome this difficulty. By closely enwinding two coils that are connected in opposed-polarity series on the HCT, the original magnetic field in the core produced by a single external current source can more accurately be simulated. Thus, the performance of the HCT under working conditions can equivalently be tested in a laboratory. By using two pairs of such coils, which are positioned at right angles to the other pair and work independently, this method can simulate the magnetic field from multiple external current sources positioned in arbitrary manner and consequently test the performance of the HCT under electromagnetic interference from multiple current sources. This new method is both accurate and effective, and easy to implement. It can be applied to overcome the testing difficulty of an HCT in a laboratory, which particularly has shielding coils. [ABSTRACT FROM AUTHOR]

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]

The advance in power electronics causes, over the years, an increasing diffusion of nonlinear loads. Moreover, electrical generation systems are going to include a growing amount of solar and wind energy, characterized by time-variant flow of energy and, very often, with a relevant distortion. These aspects give more and more emphasis to the monitoring of conducted disturbances on power systems over a wide frequency range, and consequently, voltage and current transducers adopted for this aim must have a proper frequency bandwidth. Voltage transformers (VTs) and current transformers (CTs), which are the most installed transducers in electrical power systems, are typically constructed to operate only at the industrial frequency, i.e., 50/60 Hz, but it is clear that their substitution would require an unsustainable cost. Therefore, in this paper, a method for real-time digital compensation of the CT frequency response over a wide range is presented. An implementation of the proposed method is shown, and the compensated CT is characterized and tested in some practical situations, with waveforms affected by typical power quality disturbances. [ABSTRACT FROM AUTHOR]

This paper presents the operating principle, the performance under impulse condition, and the design of a selfintegrating Rogowski coil for measuring high-impulse currents. Oscifiatory and overdamped unidirectional impulse currents are generated up to 10 kA and measured by different methods, namely, two commercial impulse current transformers, a resistive shunt, and the newly designed self-integrating Rogowski coil. For the resistive method, the voltage drop across the shunt affects the total voltage measured across the test object and causes distortion in the case of simultaneous measurement by an impulse current transformer having a small aperture. The Rogowski coil theory under impulse current conditions is presented. The concept of transmission lines is used, and the line parameters are optimized to achieve a self-integrating mode and avoid spurious effects of reflections and stray capacitances. The output voltage linearity of the designed self-integrating Rogowski coil is checked using different linear and nonlinear loads and coil termination resistances. It is found that at a termination resistance of 1 Ω, satisfactory impulse current waveforms are measured by. taking the commercial impulse current transformer as a reference signal. Results reveal that the measurement errors for the current peak and front and tail times are ±2%, ⩽6%, and ⩽12%, respectively. Overdamped impulse currents are generated by different generator capacitances, where comparisons between the measured and calculated current waveform parameters have shown good agreement. [ABSTRACT FROM AUTHOR]

Bandwidth is one of the important performance parameters of current transformers. Transformers are required to have adequate bandwidth to regenerate the measured current, apart from uncertainties that are caused by the nonsinusoidal waveforms along with harmonics. An expression for the transresistance of the current transformer in terms of parasitic components is derived. Approximate expressions for lower cutoff frequency, upper cutoff frequency, and bandwidth are derived from the equivalent models of the current probe in the corresponding frequency range. The expressions are validated by experimental results for a current transformer using a Ferroxcube ferrite core 528T500-4C4. An overview of the effects of different parasitic components, such as magnetizing inductance, leakage inductance, and stray capacitance, on the bandwidth of a current transformer is presented. [ABSTRACT FROM AUTHOR]

The current transformer (CT) performance under distorted waveform conditions is usually characterized by means of the frequency-response test. In this paper, a new way to characterize CTs, closer to real operation conditions, is proposed. The harmonic phase-angle and ratio errors are measured using a nonsinusoidal current composed of fundamental and one harmonic with adjustable phase shift. The new method was tested by determining the performance of two metering class CTs commonly used by the Italian power company. The errors measured using the proposed approach are larger than the ones obtained with the frequency response. This result suggests that the frequency-response approach for the evaluation of CT performance under distorted waveform conditions is not a reliable method. [ABSTRACT FROM AUTHOR]

This paper describes a reference current-measuring system for the onsite calibration of high-voltage current transformers. The reference current-measuring system consists of a Rogowski coil, a current shunt, two digitizing voltmeters, and a computer to control the voltmeters. The method of generation of the high current and the uncertainty of the calibration are discussed. The results of a calibration performed onsite on a 400-kV substation are presented. Uncertainties of 300 μA/A for ratio and 1 angular minute for phase displacement were achieved with this method onsite. [ABSTRACT FROM AUTHOR]

An intercomparison of the calibration systems for instrument transformers between the Korea Research Institute of Standards and Science (KRISS) and the National Research Council of Canada (NRC), with many different ratios at 60 Hz, was performed using six portable transfer standards. The portable transfer standards consist of two current transformers (CTs) with current ratios of 5 A15 A up to 20000 A/5 A and four voltage transformers (VTs) with voltage ratios of 110 V/110 V up to 66000 V/110 V. The comparison results for the CT calibration systems between the two institutes are in good agreement within 10 x 10-8 for ratio and 10 μrad for phase for all the current ratios. The comparison results for the VT test systems also indicated good agreement within 35 x 10-6 for ratio and 35 μrad for phase for all voltage ratios. [ABSTRACT FROM AUTHOR]

In this paper, an overview of the development and performance of special compact-and-lightweight wideband high-current multistage current transformers for precise measurements of current harmonics at the National Research Council of Canada is described. These include current transformers with ratios of 1000 A/5 A and higher, with ratio errors of less than 5 × 10-6 in both magnitude and phase with burdens up to 0.5 and at frequencies up to 5 kHz. [ABSTRACT FROM AUTHOR]

This paper investigates the practice of correcting the results of no-load loss measurements of power transformers for the effect of distorted supply voltage waveform. A three-phase 700-MVA power transformer is tested twice: first with its low-voltage windings connected line-to-neutral, with nearly sinusoidal test voltage conditions, and then for the second test with its windings connected line-to-line with more distorted voltage waveforms. The test data obtained during the measurement was reproduced at the National Research Council (NRC) Laboratory to demonstrate the limits of the application of the loss correction formula currently used. [ABSTRACT FROM AUTHOR]

Proposes an original electronic device for compensating ratio and phase-displacement errors of measuring current transformers and clamp-on probes. Description of the method; Application example of the proposed system.