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The fundamental frequency of power system may deviate from the nominal value due to various reasons, such as load variation, subsynchronous resonance and fault occurrence. The maximum frequency deviation considered by the latest IEEE standard is 5 Hz. This paper proposes a dynamic harmonic synchrophasor estimator, which can accurately estimate the dynamic harmonic parameters even if the frequency deviation reaches 5 Hz. Multiple discrete frequencies are generated at a fixed frequency interval on both sides of the nominal frequency, and multiple dynamic harmonic filters are generated offline based on those frequencies. The windowed interpolation discrete Fourier transform is adopted for online monitoring of the fundamental frequency. According to the detected frequency, a harmonic filter, which is generated with the discrete frequency that is closest to the detected frequency, can be selected to analyze the dynamic harmonic synchrophasor, frequency and rate of change of frequency. The performances of the proposed estimator are verified through tests under various frequency deviation conditions, and the test results show that the proposed estimator can accurately estimate the dynamic harmonic parameters when the frequency deviation is within 5 Hz. [ABSTRACT FROM AUTHOR]

Recently, the current transducer based on an array of magnetic field sensors has attracted a lot of attention. For busbars of circular cross section, many studies have been conducted and many results have been obtained. However, for the rectangular cross section busbar, the skin effect causes the frequency response curve of the magnetic flux density $B$ generated by the current-carrying conductor to appear nonlinear, which brings challenges to the wideband current measurement of the rectangular busbar. This article presents a wideband current transducer based on the array of magnetic field sensors for the current measurement of the rectangular busbar. First, according to the rectangular busbar, select reasonable magnetic field detection points to arrange the sensor array. Then, the frequency response curve of the magnetic flux density $B$ at each detection point around the rectangular busbar is obtained by simulation. After that, all frequency response curves are averaged, and the proper digital filter is designed according to the averaged frequency response curve to perform frequency compensation. The compensated frequency response curve is basically flat, so the wideband current measurement of the rectangular busbar can be realized. The bandwidth and overall performance of the designed wideband current transducer are verified through experiments, and experimental results show that the designed transducer can meet the requirements of relevant standards for the class 0.5 current transducer. [ABSTRACT FROM AUTHOR]

The knowledge of current density distribution gives important information for the study of the electric arc in low-voltage circuit breakers. Available experimental approaches to investigate the electric arc behavior include electrical measurements, optical, and magnetic diagnostic techniques. However, noninvasive experimental methods able to obtain the electric arc current density cannot be found in the literature. This article presents a nonintrusive diagnostic technique able to reconstruct the 3-D electric arc current density from its magnetic field measurements by solving a magnetic inverse problem. This inverse problem is known to be ill-posed, and Tikhonov regularization is used together with the L-curve method. Zero-divergence condition on the current density and boundary conditions are incorporated into the formulation of the inverse problem with the help of Whitney elements. A magnetic field measurement system is developed based on a Hall-effect magnetic sensor array and a data acquisition board. The sensor array is composed of 64 mono-axial analog-bipolar sensors distributed in eight columns and eight rows. The maximum measurable magnetic field of the sensor is 9 mT. The data acquisition board consists of eight analog-to-digital converters with a maximum sampling rate of 200 kHz and a 16-bits resolution. Experimental tests are carried out using the proposed method in order to study the arc dynamics. The reconstructions are compared with those of an optical diagnostic technique based on a charge-coupled device (CCD) camera. [ABSTRACT FROM AUTHOR]

The unique gate failure mode of SiC MOSFETs is often identified but has not been fully understood yet. In this letter, post-failure cell inspections demonstrate that its main cause is the crack at the SiO2 dielectric layer with melted source aluminum inside. An electro-thermal-mechanical simulation is performed to reproduce the failure transition, and it reveals that the crack forms at an early stage. This new failure mechanism further enlightens on the vulnerability of the vertical power MOSFET structure in extremely high-temperature operation. [ABSTRACT FROM AUTHOR]

Aging precursor identification is crucial to achieving online condition monitoring and estimating the remaining lifetime of insulated-gate bipolar transistors (IGBTs). However, existing failure precursors are limited with respect toin situmonitoring. In this paper, the duration of the Miller plateau during the IGBT turn-ontransition is proposed as an online precursor indicating two dominant types of failures. Based on the theoretical closed-form expressions, the adverse effects of package-related bond wire fatigue and chip-related gate oxide degradation on the Miller plateau duration are explained. By using a dedicated online measurement system that is implemented on the gate driver side, the proposed precursor is extracted during operation. Discrete IGBTs of two gate structures are employed during the accelerated aging tests. Negative and positive degradation trends of the Miller plateau duration under power cycling and high electric field stress, respectively, are revealed, thus illustrating the validity of the proposed method. Finally, the main differences in physics-of-failure between two types of aged devices are investigated using post-failure analysis. The innovation of applying the Miller plateau duration as a failure precursor involves its ability to accomplish real-time field monitoring and its sensitivity to multiple failure mechanisms. [ABSTRACT FROM AUTHOR]

Current density distribution in electric arcs inside low-voltage circuit breakers (LVCBs) is a crucial parameter for us to understand the complex physical behavior during the arcing process. In this paper, we investigate the inverse problem of reconstructing the current density distribution in arcs by inverting the magnetic field. This paper is focused on the modeling and computational phase for the magnetic inverse problem when linear ferromagnetic regions are considered in the model. To address the ill-posedness of the inverse problem, the standard method of least-squares approximation by Tikhonov regularization is studied, complemented with the generalized cross-validation criterion for regularization parameter selection. Considering the inclusion of a ferromagnetic region, two regularization approaches have been analyzed for the formulation of the currents in splitters and their corresponding magnetic field contribution. Effects of several features on the performance of the regularized solution have been investigated, including the signal-to-noise ratio, the value of permeability of the splitters, and the measurement distance. The numerical tests show the direct accessibility for the 3-D current density distribution with the proposed scheme, providing the accuracy and robustness for the applicability to study the arc behavior in LVCBs. [ABSTRACT FROM AUTHOR]

This paper presents a systematic analysis of the influence of magnetic measurement modeling on the regularized solution of magnetostatic inverse problems. The focus is on the application of the inverse problem technique to current distribution reconstruction of arc plasmas inside low-voltage switching devices. The inverse problems modeled with both the ideal sensor assumption and non-ideal sensor modeling are studied, considering the geometry and active area of sensors. The Tikhonov regularization is adopted to address the ill posedness of the inverse problem. Sensor arrays with random variations in sensor directions and positions are compared with arrays using perfectly aligned setup. The numerical results reveal that for mono-axial planar sensor arrays the ideal sensor assumption could be used to simplify the modeling process with serious environmental noises. Better reconstruction can be obtained using the non-ideal sensor model when the sensor variations are large. [ABSTRACT FROM AUTHOR]

Dynamic contact resistance measurement (DRM) has been widely used in evaluating the contact condition of circuit breakers from 20 years ago. With the increasing of the injected current, the contact resistance is lower than it was. It is considered that the contact hardness, contact force, and specific resistivity are affected by the injected current. SF6 circuit breaker with self-elastic contact is studied in this paper because of its widely used in high-voltage power system. First, the parameters of the dynamic curves are discussed, and the contact resistance in arcing contact part is concerned because of its susceptibility. Second, the mathematical model of contact force is discussed and calculated, and the change of contact force under a different injected current can be ignored. Finally, the mathematical model of contact resistance and injected current is established, when the breaker contact speed is stable. The mathematical model is proven effective by DRM tests. [ABSTRACT FROM AUTHOR]