Rogowski Coil Research Articles

Development and Performance Analysis of the Rogowski coil sensor for Arcing Fault Measurement

Arcing fault is an overvoltage that usually occurs in the power system network, and it is necessary to monitor this phenomenon in electrical equipment. This paper presents the Rogowski coil (RC) as an arcing fault sensor. Finite element method (FEM) software used for analysing the RC magnetic flux density with two types of RC with the different turns and size demonstrated. The sizing of RC based on the 240 mm2 cross-link polyethene (XLPE) 11 kV underground cable. The prototypes of the RC sensors were designed using Solidworks software and three-dimensional (3D) printer for fabrication purposes. The main objective of the experiment is to investigate the RC effect with high magnetic flux density by implementing in real measurement. An experimental setup for real arcing fault with various voltages (up to 15 kV) was conducted to verify the RC performance, such as sensitivity and bandwidth range. The result has shown that the bandwidth of RC 1 is higher than RC 2 in all measurement by 22.6%.

Experimental Study on High Frequency Pulse Current Variation Characteristics of Pollution Discharge of Insulators

Pollution flashover of insulators is an important factor causing trip of transmission lines and even large-scale blackouts of power grids. At present, the research on pollution discharge of insulators mainly focuses on leakage current monitoring, while leakage current detection mainly focuses on the low-frequency components of the discharge process, and the research on high-frequency discharge characteristics is rare. In this paper, the voltage is monitored based on the coupling capacitance partial voltage method. The high-frequency current is monitored based on the Rogowski coil principle. The characteristics of high frequency pulse discharge in safety zone, forcast zone and danger zone are analyzed. The results show that the pulse amplitude and repetition rate increase significantly with the increase of discharge. The statistical law of high frequency pulse current can reflect the severity of pollution discharge and realize early warning.

Structure and modelling of four‐layer screen‐returned PCB Rogowski coil with very few turns for high‐bandwidth SiC current measurement

Accurate measurement of current through a silicon carbide (SiC) device is especially challenging, because of its fast switching speed. Its accompanied current sensor must hence have a high-bandwidth and a high-noise immunity. It must also not interfere with operation of the device. Due to these, the printed-circuit-board (PCB) Rogowski current sensor is particularly suitable, but normally requires many layers. With only four layers, the existing Rogowski coils are not yet capable of shielding ambient voltage and magnetic noises simultaneously. Moreover, their computed and measured self-inductances are usually very different with errors as high as 45% reported in the literature. To resolve these issues, an alternative four-layer screen-returned PCB coil has been presented. The described coil uses very few turns to preserve its high bandwidth at the expense of even tougher determination of its self-inductance. An alternative piecewise modelling method has therefore been proposed for finding its self-inductance, needed for designing its theoretical bandwidth. These, together with a non-inverting integrator, permit current through an SiC device to be measured accurately, as demonstrated experimentally.

Study on Additional Dynamic Component of Electronic Current Transducer Based on Rogowski Coil and Its Test Approach

Electronic current transducers based on Rogowski coil are commonly used for power system protection. However, they may generate additional dynamic components in some cases that may cause misoperation of protection devices. In order to check the hidden danger of this undesired phenomenon, this article studies the transfer characteristics of Rogowski coil and proposes an approach to detect the possible occurrence of the additional dynamic component phenomenon. First, the root cause for the appearance of additional dynamic component is analyzed and investigated. Then, using the electromagnetic transient simulation modeling and variable delay scanning method, the simulation data of the grid operation are injected into the actual acquisition unit and the integral unit to obtain the output response of the current transducer. Therefore, the additional dynamic component phenomenon can be reproduced and identified. Finally, the test results of the application example demonstrate the effectiveness of the proposed method.

Measurement of high frequency magnetic properties of electrical steel sheet using prototype Rogowski coil

In order to develop a high-efficiency, low-loss, small, high-power, high-speed rotating motor, it is necessary to accurately measure the magnetic properties of electrical steel sheets under PWM excitation. A shunt resistor is generally used for measuring magnetic characteristics, but non-contact current measurement is required. However, iron cores are used in commercially available current measurement sensors, and it is necessary to consider the effects of core characteristics on high-frequency currents. The authors are focusing on Rogowski coils and developing small current / magnetic field sensors specialized for motor and electrical steel sheet evaluation. In this paper, we make a prototype of Rogowski coil, and report on the evaluation of basic electrical characteristics and the results of application to the measurement of magnetic characteristics of electrical steel sheets under sinusoidal excitation and PWM excitation.

Inference of X-Ray Emission From a Plasma Focus Discharge: Comparison Between Characteristic Parameters and Neural Network Analyses

Pulsed plasma discharges, such as the plasma focus, are a source of pulsed X rays, therefore it is desirable to understand the relationship between this fast transient phenomena and the electrical variables of the discharge. Parameters from the electrical diagnostic signals are typically used to characterize the plasma focus discharge and for the correlations with X rays measurements via scatter plots. To further evaluate relevant information in the electrical signals, besides the characteristic parameters, an implementation of different types of machine learning algorithms, that included deep learning, was performed. A classification of pulses associated with an X rays measurement, in terms of the electrical signals data as input, was carried out. Two approaches were compared: the selection of the characteristic parameters and the use of the entire signals so the algorithms could find additional information for the classification task. The electrical diagnostic signals corresponded to: the voltage at the electrodes of the discharge chamber measured with a resistive voltage divider; time variation of the circuit current measured with a Rogowski coil and an inductive loop sensor; and the electromagnetic burst from the circuit measured with a Vivaldi antenna. The X rays measurement corresponded to the signal obtained from a scintillator-photomultiplier. In terms of the performance of the algorithms models in this classification problem, the results indicated that there is no significative improvements when using the entire signal or the selection of characteristic parameters. The best results were obtained when the following parameters were used: voltage at time of gas breakdown, voltage at time of pinch, current at time of pinch, time derivative of current at time of pinch, time from breakdown to pinch, and the Fast Fourier Transform of the part of the Vivaldi antenna signal related to the pinch event.

Dynamic Arc Current Distribution of Parallel Vacuum Arcs Subjected to Bipolar Axial Magnetic Field

The objective of this paper is to determine dynamic anode and cathode arc current distribution of parallel vacuum arcs subjected to bipolar axial magnetic field. Drawn arc experiments were carried out in a demountable vacuum chamber. A split bipolar axial magnetic field electrode with diameter of 100 mm was specially designed. Arc current of two half split electrode discs were measured through Rogowski coils out of the vacuum chamber. Experimental current ranged from 4.5 to 45.0 kA. Vacuum arc behaviors were recorded by a high-speed camera. Unbalance phenomena of anode current and cathode current of parallel vacuum arcs were observed. The maximum average anode and cathode current density difference between parallel vacuum arcs at current of 45.0 kA were 2.57 and 2.52 A/mm 2 , respectively. Critical value of both anode and cathode current difference ratio at time instant of maximum arc current difference with different arc initial conditions was 0.60. The maximum critical value of time instant of maximum anode and cathode current differences between parallel vacuum arcs with one strong arc branch at arc initial were 3.5 and 4.0 ms, respectively. Moreover, a three-interval arc current development model was proposed to describe unbalance phenomena of parallel vacuum arcs.

Relaxation characteristics of ion jet formed across the short air gap in the cone–sphere electrode under positive polarity DC voltage

The research into the development of discharge under positive polarity voltage across the short air gap is of great significance to improve insulation of electrical equipment. By establishing a photoelectric joint detection system, this study observed phenomena in short air gaps before, and the period of breakdown. By utilising a photomultiplier tube and a Rogowski coil, the optical and current signals were obtained. Moreover, through z-type Schlieren system and high-speed digital camera, relaxation images of ion jet formed across cone–sphere electrodes were obtained. Through comparison and analysis, the discharge of short air gap was divided into three stages: initial corona, strong corona and streamer breakdown. On the basis of this, the relationship between optical and current signals was compared by assessing characteristics of the ion jet in each stage. Also, the relaxation characteristics of an ion jet were analysed. The results showed that ion jets appeared in the initial corona stage, while relaxation channel of the ion jet was formed and the channel fluctuated in the strong corona stage. In the streamer breakdown stage, the process of expansion, constant fluctuation and breakdown appeared; the amplitudes of corona current signals and optical signals in these three stages constantly increased.

A novel high power vacuum diode with a focusing electrode for effective operation in a low guiding magnetic field.

A novel diode featuring an annular cathode and a ring-shaped focusing electrode and operating in a low guiding magnetic field (GMF) has been developed. It was found that the breakdown threshold for a focusing electrode made of titanium was 140 kV/cm higher than a stainless steel electrode for the same operating conditions. Comparison of the diode current measured by a Rogowski coil and the beam current measured by a Faraday cup at the collector indicated that an intense relativistic electron beam was transmitted effectively even in a GMF of as low as 0.21 T. In addition, a photo of the cathode plasma and the targeting results indicated that the emission uniformity of the graphite cathode was satisfactory.

Functional test of electron beam extraction for pulse electron irradiator

Function test of electron beam extraction for pulse electron. The functional test of pulse electron beam extraction has been performed. The purpose of the functional test is to know the magnitude of the current and the distribution of the extracted electron beam. The plasma current detection system consists of three Rogowski coils mounted on output cables of Ignitor Discharge Power Supply (IDPS), Arc Discharge Power Supply (ADPS) and Faraday Cup (FC), while the voltage and pulse width are observed using an Oscilloscope. From the measurement results obtained that the spot and plasma currents are 11,24 A and 119,65 A. At the extraction voltage of 3 kV obtained the maximum extraction current are 13,1 A and 6,7 A for the position of FC near the ignitor electrode and in the middle of the grid respectively. It can be concluded that the pulsed electron beam can be extracted by the distribution of the beam near the ignitor electrode higher than in the middle position of the grid.

THE MAGNETIC FLUX DENSITY OF VARIOUS GEOMETRIES OF ROGOWSKI COIL FOR OVERVOLTAGE MEASUREMENTS

Overvoltage phenomenon is the common problem that always occurs in the power system and can cause the electrical system network breakdown, and in some cases, it may explode. The frequent overvoltage also can affect and degrade the lifespan of the electrical power system components and network. Thus, the overvoltage sensor is needed to overcome this problem matter. The Rogowski coil (RC) is one of an inductive coil group, and it is suitable for measuring the alternating current (AC) and transient currents or overvoltage. This paper demonstrated the effect of RC magnetic flux density, B with difference cross-section, geometries sizing and the number of turns by using Finite Element Method (FEM). Commonly, there are three types of RC widely used; rectangular, circular and oval. Each of these cross-sections has different characteristics in term of performance. The results have shown that the rectangular cross-section is better than oval and circular cross-section based on the number of magnetic flux density.

Deep neural network Grad–Shafranov solver constrained with measured magnetic signals

A neural network solving the Grad–Shafranov equation constrained with measured magnetic signals to reconstruct magnetic equilibria in real time is developed. The database created to optimize the neural network’s free parameters contains off-line EFIT results as the output of the network from 1118 KSTAR experimental discharges of two different campaigns. Input data to the network constitute magnetic signals measured by a Rogowski coil (plasma current), magnetic pick-up coils (normal and tangential components of magnetic fields) and flux loops (poloidal magnetic fluxes). The developed neural networks fully reconstruct not only the poloidal flux function but also the toroidal current density function with the off-line EFIT quality. To preserve the robustness of the networks against missing input data, an imputation scheme is utilized to eliminate the required additional training sets with a large number of possible combinations of the missing inputs.

A parametric method for correcting polluted plasma current signal and its application on Keda Torus eXperiment.

We have developed a parametric method for eliminating the background component of the plasma current, which is measured by a Rogowski coil and polluted by the toroidal magnetic field in the vacuum vessel of the Keda Torus eXperiment (KTX) reversed field pinch (RFP) device. The method considers the toroidal magnetic field windings, the KTX vacuum chamber, and the Rogowski coil as a linear time-invariant system; in this case, a constant frequency response function characterizes the system. Using this response function, the current component caused by pollution from the toroidal magnetic field can be predicted exactly for an arbitrary input current to the toroidal magnetic field windings. Compared with the traditional proportional compensation method, the proposed method has great flexibility and universality and it is potentially applicable to cases in which the toroidal field current signal changes over time with plasma feedback signals. Furthermore, the method can be applied to other similarly affected signals, such as magnetic field signals. As an example, we have corrected the poloidal and toroidal magnetic field signals better to reveal the true physical processes for the RFP state.

Development of smart online partial discharge monitoring system for medium voltage power cable

This paper presents, the development of smart online partial discharge (PD) monitoring system for medium voltage (MV) underground power cable. PD monitoring is the highly efficient tool to monitor insulation degradation for high voltage (HV) equipment in order to avoid failures or breakdown. Selection of improved technology and performance of PD detection sensor, effective measurement technique and smart user friendly of graphical user interface (GUI) system are contributed towards the development of efficient monitoring system. This paper addresses three main aspects which are needed in completing the monitoring system. They are, the use of Rogowski coil (RC) as detection sensor, processing unit using Alterra board and integrated with GUI PD monitoring system for underground cable using LabVIEW. The monitoring system is compared to the conventional method with the PD signal used is measured from the real on-site measurement in order to analyse its performance. The analysis is performed in MATLAB and LabVIEW software’s environment and the maximum peak of PD signal is enabled to view using GUI which complete with the location information of PD source. Furthermore, this paper has contributed to solve the problem in selection the simplified and practical approach for PD sensor and monitoring system. In the perspective of automated condition monitoring, this smart online PD monitoring system provides a complete solution towards latest industrial revolutions

Performances of regression model and artificial neural network in monitoring welding quality based on power signal

In this study, a systematic research was conducted to compare the performances of the regression model and artificial neural network in predicting the nugget diameter of spot-welded joints by monitoring the dynamic power signature. The TC2 titanium alloy with a thickness of 0.4mm was used as the welding material, and a high-frequency precision spot welder was used to join the titanium alloy sheets. The dynamic welding current curve was obtained using the Rogowski coil, while the voltage curve was detected via two leads clipped onto the upper and lower electrodes during the entire welding process. The variations in the welding power signal in the welding process were investigated, and the characteristics of the power signals for different welding currents and electrode forces were analyzed. The power signals of different types of welding joints varied significantly. Five characteristics were extracted from the power signal to describe the shape of the curve. The stepwise regression analysis and back propagation neural network were respectively used to classify the welding joints into three categories: bad welds, good welds, and welds with expulsion. The performances of the two established prediction models were compared, and their behavioral discrepancies were attributed to their own data-mapping capabilities.

Effects of Multiple Influence Quantities on Rogowski-Coil-Type Current Transformers

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.

Development of a mathematical model for determining the EMF of the secondary winding of a measuring current transformer based on the Rogowski coil

This article is devoted to the development of a mathematical model for determining the electromotive force (EMF) of the secondary winding of a measuring current transformer based on a Rogowski coil. The study focuses on determining the EMF in the secondary winding of the current transformer at different positions of the primary bus, its forms, as well as the overall dimensions of the whole measuring equipment. The study was conducted on the basis of finite element modeling and elements of the experimental design techniques. Finite-element models have been developed for various primary bus shapes in the Femm program. Regression models were obtained for determining the magnetic flux passing through the Rogowski coil in order to determine the EMF in the secondary winding using the Statistica program. The research results showed the importance of taking into account the position of the primary bus relative to the center of the Rogowski coil, as well as the influence of the shape of the primary bus on the measurement result of EMF in the secondary winding of the current transformer.

Start-Up Studies of GLAST-III Spherical Tokamak in the Presence of Poloidal Field

GLAST-III (glass spherical tokamak) is a small device having an aspect ratio of two (R/a = 2) with major radius R = 20 cm and minor radius a = 10 cm. Experiments are performed to examine the effect of increasing the poloidal field (PF) produced by poloidal coils as well as to study the effect of the inductance of PF coils on the plasma current formation. To investigate the GLAST-III plasma, several diagnostic tools such as Rogowski coil, loop voltage, photodiode, Optical emission spectroscopy, high-speed camera, and Langmuir probe are used. After optimizing the working pressure, the first experiment is performed using toroidal field coils and central solenoid along with radio frequency (RF) pre-ionization source. A plasma current of 1 kA is achieved for 1.2 ms. In later experiments, the effect of the poloidal magnetic field is also included. It is observed that with increasing the PF, the plasma current increases, attain a maximum value (5 kA) and then after a critical value of the applied poloidal magnetic field, the plasma current starts decreasing. Similarly, with the inclusion of inductor in series with the PF coils, the plasma current value is reduced and its pulse duration is increased. Both optical emission and Langmuir probe diagnostics results show a similar trend of the plasma current.

Research on Small Square PCB Rogowski Coil Measuring Transient Current in the Power Electronics Devices.

With the development of China’s electric power, power electronics devices such as insulated-gate bipolar transistors (IGBTs) have been widely used in the field of high voltages and large currents. However, the currents in these power electronic devices are transient. For example, the uneven currents and internal chip currents overshoot, which may occur when turning on and off, and could have a great impact on the device. In order to study the reliability of these power electronics devices, this paper proposes a miniature printed circuit board (PCB) Rogowski coil that measures the current of these power electronics devices without changing their internal structures, which provides a reference for the subsequent reliability of their designs.

Disruptive plasma simulations in EAST including 3D effects

A simulation of a disruption in the experimental advanced superconducting tokamak (EAST) is carried out with the CarMa0NL code and the results are successfully compared with the experimental data. The fundamental role of three-dimensional (3D) features of conducting structures surrounding the plasma is demonstrated and is fully accounted for in simulations. The results demonstrate that the currents measured by Rogowski coils placed around the supports of in-vessel plasma facing components (PFCs) are largely due to eddy currents induced by the plasma motion and current decay, with a relatively small contribution coming from the currents directly injected from the plasma into the structures (halo currents).