Characteristics Of Current Transformers Research Articles

Design and optimization of line CT energy harvesting device

Abstract The aim of this study is to design and optimize an energy harvesting device for line current transformers (CT). The main function of this device is to extract energy from CT on the line to supply power to related electronic devices such as sensors and monitoring equipment. Firstly, an in-depth analysis of the working principles and characteristics of CT was conducted to determine the design requirements and performance indicators of the energy harvesting device. Subsequently, an energy-harvesting device based on the principle of magnetic coupling was designed. Different circuit principles were developed to accommodate low-load and high-load scenarios on the line, and the structure and parameters were optimized to improve energy conversion efficiency and output stability. Through experimental validation, the performance and stability of the designed energy harvesting device under different working conditions were verified. Finally, the design scheme of the energy harvesting device was optimized, and further improvement and application suggestions were proposed. This study provides a theoretical and practical basis for improving the performance and reliability of line CT energy harvesting devices, which is of great significance for the safe operation of power systems and equipment monitoring.

Real-Time Detection Method for Saturation Speed of Air-Core Coil Current Transformer

Traditional methods generally rely on a fixed threshold to determine whether the current transformer is saturated. However, this threshold based judgment method is difficult to adapt to different working conditions and changes in current waveforms. In view of the different characteristics of current transformer and the diversity of working environment, it may not be accurate to judge its saturation state only by relying on a fixed threshold. In order to improve the efficiency of current transformer speed saturation detection and reduce the error, a new type of air core coil current transformer speed saturation real-time detection method is proposed. Based on the working and current characteristics of the fast saturation current transformer, the discrete Fourier algorithm is used to suppress power frequency interference signals, with the fundamental frequencies set to 45 Hz and 55 Hz respectively, in order to separate the signal from power frequency interference and reduce the interference intensity of the power frequency interference signal; Identify all faults and saturation points, and extract effective data segments. The wavelet transform characteristics of the secondary current waveform of current transformer in saturated and unsaturated states are deeply studied. By analyzing the changes of different operating conditions and current waveforms, more discriminant features are extracted by using the characteristics of wavelet transform, so as to realize the real-time and accurate detection of saturation state. The results indicate that after adopting the proposed method, the highest accuracy of data segment extraction reached 97%; The maximum detection error is only 4%. The detection time is only 1.31 s. This indicates that the proposed method improves the detection performance and is practical.

Feasibility study on substitution of SF6 insulated current transformer with environment-friendly natural gas

Many SF6 gas-insulated current transformers (CT) are used in the power grid. The global warming potential (GWP) of SF6 is 23,900 times that of CO2, and the leakage of SF6 will aggravate the global warming trend. It is a hot issue to carry out the study of environment-friendly gas substitution in the power grid. This paper systematically studied the voltage withstand, partial discharge, and temperature rise characteristics of dry air, N2, and CO2 gas-insulated CTs. Through the study, the permissible critical pressures in environment-friendly gas-insulated CTs were determined to be 0.9 MPa for dry air, 0.7 MPa for N2, and 0.8 MPa for CO2, respectively. The partial discharge intensity was less than 5 pC for environment-friendly gas-insulated CTs at 0.3 MPa∼0.8 MPa pressure. The experimental results of temperature rise characteristics showed that under the condition of a 600A rated operating current, the maximum temperature rise of the CTs was about 80 °C, and the maximum temperature rise happened at the conductive rod. The experimental results verified that environment-friendly gases could meet the requirements of insulation and temperature rise. Due to the increase of pressure in CTs, the action pressure of the explosion-proof membrane should be changed to meet the mechanical strength requirements. It is recommended that when using 0.9 MPa dry air, the action pressure should be designed as 1.8 MPa; when using 0.7 MPa N2, the pressure should be designed as 1.4 MPa; when using 0.8 MPa CO2, the pressure should be designed as 1.6 MPa. The results of this paper can provide a reference for development of environment-friendly gas-insulated CTs.

Analysis of the Metrological Characteristics of Current Transformers Based on the Results of Periodic Verification

The article analyzes the results of verification of measuring current transformers of various types. Based on the results of the analysis, the dependences of the metrological characteristics of measuring current transformers on their type were revealed. A conclusion is made about the applicability of the identified dependencies for assessing the quality level or predicting metrological failures.

Research on Consistency of Transient Response Characteristics of Current Transformers for DC application in DC Engineering

In ultra high voltage(UHV) DC system, the transient characteristics for fault current monitoring of current transformers for DC application (DCCTs) and the consistency of response characteristics when different types of DCCTs are used for differential protection have become important factors affecting the safe and stable operation of DC system. In this paper, transient characteristics of all-fiber DCCTs and shunt DCCTs mainly used in DC system were studied, the main parameters of the transient characteristics including delay time and maximum peak instantaneous error were tested, and the key parameters influencing the response consistency of DCCTs were analyzed. The results show that the maximum peak instantaneous errors of all-fiber DCCTs and shunt DCCTs can meet ±5% limit requirement, meeting the demand for protection application in DC system. The delay time is the main factors affecting the maximum peak instantaneous error of DCCT. The longer the delay time is, the greater the maximum peak instantaneous error is, which may even exceed the limit value of ±5%. If necessary, the delay time of DCCTs participating in differential protection can be compensated. The research results provide a theoretical basis for preventing the malfunction of protection device caused by the inconsistent response characteristics of DCCTs in DC system.

МЕТОДИКА РАСЧЕТА УТОЧНЕННЫХ ХАРАКТЕРИСТИК ТРАНСФОРМАТОРОВ ТОКА ДЛЯ ПОВЫШЕНИЯ ЭФФЕКТИВНОСТИ РАБОТЫ УСТРОЙСТВ РЕЛЕЙНОЙ ЗАЩИТЫ

A method has been developed for selecting the technical characteristics of current transformers and connected relay protection devices that ensure the reliability of the power supply system in accord-ance with modern requirements

Experimental obtaining characteristics of current transformers for developing their models and determining the time of saturation of the magnetic circuit

Electromagnetic current transformers (CT) are subject to saturation and residual magnetization of a magnetic circuit. This phenomenon has an impact on the operation of devices of commercial accounting of electric energy and relay protection and automatics (RPA). Saturation of the current transformer’s magnetic core can lead to emergency situations due to incorrect operation of the protections and excessive disconnection of the protected connections. At the moment, Russian norms do not regulate the work in transient modes, including short circuits with an aperiodic current component. The Ivanovo State Power Engineering University (ISPEU) conducts research on the topic of determining the time to saturation of CT at short circuit. The purpose of the work was to develop an algorithm for monitoring saturation and determining the time to saturation of the CT magnetic core, in order to ensure the correct operation of the RPA in all modes. The article is devoted to the method of construction and research of mathematical models of CT for calculating the time to saturation. The general structure of the algorithm for determining the time to saturation is presented.

Reliability of an Automatic Adjustable Current Transformer

In the article the reliability calculations of automatic transformers with adjustable range are performed. Since reliability is one of the main characteristics of current transformers, several parameters of its range are included in the calculation of the reliability of an automatic adjustable current transformer, and as a result, high-precision values of reliability were achieved.

The Influence of Thermomagnetic Treatment of Cores of Amorphous Magnetic Materials on the Metrological Characteristics of Electromagnetic Transformers of Current

We consider a method of thermomagnetic treatment of amorphous magnetic material cores in a transverse constant magnetic field designed to improve the metrological characteristics of current transformers. The effectiveness of the method is due to a significant increase in the magnetic permeability of the cores of current transformers. The use of thermomagnetic processing makes it possible to increase their precision class.

Анализ и проверка соответствия характеристик трансформаторов тока класса P условиям функционирования первых ступеней дистанционных защит линий электропередачи при переходных процессах

The results of research of influence of saturation of the current transformers of class P transient on the operation of the relay resistance and on the direction of power the first stages of the distance protection against phase-to-phase and single-phase short circuits of production NPP EKRA Ltd. The connection diagrams of current transformers to the resistance relay and the design conditions for checking the compliance of the characteristics of current transformers with the conditions of operation of these protections are considered. It is established that the design mode for checking current transformers is a remote short circuit in the area of action. The method of checking the compliance of the characteristics of current transformers with the conditions of functioning of the first stages of remote protection in the presence of short-circuit currents of the aperiodic component is proposed.

Comparator effect on equivalence of results of calibrating current transformers

Many different high-precision systems for determining the ratio error and phase displacement of current transformers have been developed by leading specialists in the world. The latest research solutions with the use of the latest measurement tools, instantaneous sampling techniques, and analysis of sources of uncertainty have been applied in these developments. The objective difficulty is that only a limited number of specialized institutes implement such projects with the involvement of leading experts in the field of measurement and significant funds. First of all, these are the national metrological institutes of countries with high economic opportunities. At the level of conventional calibration laboratories equipped with modern facilities and highly qualified personnel, the uncertainty of measurements increases 10 times or more when calibrating precision instrument transformers. Thus, it has not been investigated to what extent the readouts of commercial comparators of different manufacturers in the calibration of instrument transformers of class 0.2S and more precise are equivalent. Determination of the equivalence level of AC comparators of different types in the day-to-day calibration of current transformers is the main objective of this research. More than 50 comparators of different types (with inductive or resistive current transducers) were investigated relative to 2 well-characterized reference current transformers. Comparison of the results obtained by two instruments with radically different principles of measurement gave a difference of 23 μA/A in ratio error and 52 μrad in phase displacement. The results of estimating the readout stability of modern comparators of serial production are also highlighted. The results of the analysis of the data obtained allow us to assume that measurement results of ratio error of about 50 μA/A have equivalence level within ±20 μA/A. The measurement results of phase displacement of about 50 μrad have equivalence level within ±15 μrad. Concerning the determination of metrological characteristics of current transformers with accuracy class 0.2S, their equivalence must be considered taking into account all exploited comparators. The results cause the question about the adequacy of the accuracy margin of the current transformer in the production to overlap the difference in the readouts of 260 μA/A and 500 μrad

Effects of geomagnetically induced currents on the transfer characteristics of current transformers

Summary With the arriving peak of the solar cycle, the effects of geomagnetically induced currents (GICs) on power systems attract more attention. The direct current magnetic bias caused by GIC has a more complex influence on the transient transfer characteristics of the current transformers (CTs) than that caused by high-voltage direct current due to its randomness and time variation. In this paper, a cosine function with lower frequency is simply adopted to simulate the time-variation feature of GIC. The mathematical analysis of CT transfer characteristics with the input of the GIC cosine model is presented based on electromagnetic equations and the excitation characteristics of the CT. Afterward, the physical model of the CT is built and tested under various input conditions. Furthermore, comparisons between the physical model and the simulation model are given to verify the reliability of the simulations. The simulation results show that the saturation level of the CT, such as partial transient saturation and deep saturation, is controlled by the magnitude and frequency of GIC and excitation characteristics of the CT. Moreover, CT saturation may affect the performance of the transformer differential protection, to which should be paid adequate attention. Copyright © 2016 John Wiley & Sons, Ltd.

Electromotive Force Characteristics of Current Transformer According to the Magnetic Properties of Ferromagnetic Core

The most common structure of the current transformer (CT) consists of a length of wire wrapped many times around a silicon steel ring passed over the circuit being measured. Therefore, the primary circuit of CT consists of a single turn of the conductor, with a secondary circuit of many tens or hundreds of turns. The primary winding may be a permanent part of the current transformer, with a heavy copper bar to carry the current through the magnetic core. However, when the large current flows into a wire, it is difficult to measure its magnitude of current because the core is saturated and the core shows magnetic nonlinear characteristics. Therefore, we proposed a newly designed CT which has an air gap in the core to decrease the generated magnetic flux. Adding the air gap in the magnetic path increases the total magnetic reluctance against the same magnetic motive force (MMF). Using a ferrite core instead of steel also causes the generation of low magnetic flux. These features can protect the magnetic saturation of the CT core compared with the steel core. This technique can help the design of the CT to obtain a special shape and size.

A New Method of Current-Transformer Saturation Detection in the Presence of Noise

The nonlinear characteristics of magnetization of a current transformer (CT) can cause waveform distortion in the secondary current, which may result in malfunction of protective relays. This phenomenon is known as CT saturation. The accurate saturation detection, with the use of digital-signal-processing techniques applied to secondary current, plays an important function in solving the problems caused by the saturation. This paper presents a new method of saturation detection, based on the first difference of the low-noise Lanczos filter. The formulation of the adaptive threshold according to the level of the signal-to-noise ratio (SNR) is presented and the detection algorithm is implemented, tested, and compared with the 3rd difference function method. The tests were performed using distorted secondary current signals generated by the real-time digital simulator and corrupted by several levels of white Gaussian noise. The results showed a high detection capability of the proposed algorithm regardless of the CT characteristics, the secondary burden, and the fault characteristics. In addition, the method showed to be robust against noise up to 40-dB SNR and suitable for real-time implementation.

Transmission Lines Distance Protection Using Differential Equation Algorithm and Hilbert-Huang Transform

This paper proposed the scheme of transmission lines distance protection based on differential equation algorithms (DEA) and Hilbert-Huang transform (HHT). The measured impedance based on EDA is affected by various factors, such as the distributed capacitance, the transient response characteristics of current transformer and voltage transformer, etc. In order to overcome this problem, the proposed scheme applies HHT to improve the apparent impedance estimated by DEA. Empirical mode decomposition (EMD) is used to decompose the data set from DEA into the intrinsic mode functions (IMF) and the residue. This residue has monotonic trend and is used to evaluate the impedance of faulty line. Simulation results show that the proposed scheme improves significantly the accuracy of the estimated impedance.

Development of Independent-Type Optical CT

Optical current transformers (CTs) have the advantages that they can be made much smaller and lighter than conventional electromagnetic induction transformers by their simple structure, and contribute to improvement of equipment reliability because of their excellent surge resistance performance. The authors consider optical CTs to be next-generation transformers, and are conducting research and development of optical CTs aiming to apply them to measuring and protection in electric power systems. Specifically, we developed an independent optical CT utilizing basic data on optical CTs accumulated for large-current characteristics, temperature characteristics, vibration resistance characteristics, and so on. In performance verification, type tests complying with IEC standards, such as short-time current tests, insulation tests, accuracy tests, and so on, showed good results. This report describes the basic principles and configuration of optical CTs. After that, basic characteristics of optical CTs including the conditions and results of verification tests for dielectric breakdown characteristics of sensor fibers, large-current characteristics, temperature characteristics, and vibration resistance characteristics are described. Finally, a development outline of the independent optical CT intended for application to all-digital substations and its type tests results are described. © 2013 Wiley Periodicals, Inc. Electron Comm Jpn, 97(1): 28–36, 2014; Published online in Wiley Online Library (wileyonlinelibrary.com). DOI 10.1002/ecj.11487

Research on Performance of Current Transformer Affected by DC Bias

This paper expatiates on the transfer characteristics of current transformer (CT) affected by DC bias. It explains the causations and approaches of the DC bias established, base on equivalent circuit models, electromagnetic equations and results of test analyze the effects of CT by DC bias. Result indicates that, the DC bias current will move error curve of instrument CTs to negative coordinate, and accelerate initial saturation time of protective CTs. Finally, simulation has been done to prove theory analysis. The presented result provides consultation for proper selection of both instrument and protective CTs.

Simulation and Analysis for Current Transformers with DC Bias and Remnant Flux

The transfer characteristics of current transformers (CT) change due to DC bias, which directly impacts the accuracy of measurement and power metering. Based on equivalent circuit models and core magnetizing characteristic, qualitatively analysis current transformer saturation increase errors of CT. Transfer errors under DC bias and remnant flux are also obtained based on J-A model of CT in PSCAD/EMTDC and full-wave Fourier algorithm to show that the ratio error and phase displacement increase with the DC bias. Based on FFT spectrum analysis to identify remnant flux and DC bias provides scientific basis for error compensation of CT.

电磁式电流互感器的GIC直流偏磁谐波分析

地磁感应电流(GIC)和运行于单极–大地回路方式的高压直流输电系统会使电力系统中的电磁式电流互感器(TA)产生直流偏磁效应，可能引起计量装置的误差和继电保护装置误动。本文分析了在GIC作用下，电流互感器的直流偏磁的产生机理，并应用PSCAD/EMTDC软件，基于电流互感器的Jiles-Atherton模型，建立了交流系统中电流互感器的直流偏磁的等效分析电路并进行仿真，研究分析了不同大小的GIC入侵电流互感器一次绕组，励磁电流畸变程度及谐波分布关系，以及电流互感器线圈变比对饱和程度的影响。 Geomagnetic induced current (GIC) and the High Voltage Direct Current (HVDC) systems under mono-polar operation may lead to DC bias of current transformers (CT), which may have an effect on transferring characteristics of CT and result in the mal-operation of metering devices and transformer differential protection. This paper analyzes the generation mechanism of DC bias of CT caused by GIC, and an equivalent analysis model for CT in the AC power system is established based on Jiles-Atherton model in PSCAD/EMTDC. This article also analyzes the distortion levels of the exciting current and its harmonics under the condition of DC bias induced by different amplitudes of GIC, and how CT ratios have effect on its saturation is discussed as well.

Development of Independent-type Optical CT

SUMMARY Optical current transformers (CTs) have the advantages that they can be made much smaller and lighter than conventional electromagnetic induction transformers by their simple structure, and contribute to improvement of equipment reliability because of their excellent surge resistance performance. The authors consider optical CTs to be next-generation transformers, and are conducting research and development of optical CTs aiming to apply them to measuring and protection in electric power systems. Specifically, we developed an independent optical CT utilizing basic data on optical CTs accumulated for large-current characteristics, temperature characteristics, vibration resistance characteristics, and so on. In performance verification, type tests complying with IEC standards, such as short-time current tests, insulation tests, accuracy tests, and so on, showed good results. This report describes the basic principles and configuration of optical CTs. After that, basic characteristics of optical CTs including the conditions and results of verification tests for dielectric breakdown characteristics of sensor fibers, large-current characteristics, temperature characteristics, and vibration resistance characteristics are described. Finally, a development outline of the independent optical CT intended for application to all-digital substations and its type tests results are described. © 2013 Wiley Periodicals, Inc. Electron Comm Jpn, 97(1): 28–36, 2014; Published online in Wiley Online Library (wileyonlinelibrary.com). DOI 10.1002/ecj.11487