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Stepped Controlled Shunt Reactors (SCSRs) have advantages of flexible control and reliable compensation and are likely to become widely used in Ultra-High-Voltage/Extra-High-Voltage (UHV/EHV) transmission systems. Very fast transients that occur in such systems will generate a Very Fast Transient Overvoltage (VFTO) in the SCSR. This may cause damage to the SCSR and lead to system losses. In this paper, the electric field strength and magnetic induction intensity are taken as the basic physical variables when these transients occur. Maxwell’s equations are used to separate the constraint sources, such as the conduction current, magnetization current, and polarization current, from the field source. Then, an all-current Partial Element Equivalent Circuit (PEEC) model for these component elements that considers the surface charge is established. Fast and accurate calculations of the inductance parameters, which involve multiple integrals, are performed using geometrical mean distances and a complex component segmentation method. The equivalent structures and circuit equations of the SCSR windings are presented, and the voltage distribution of the SCSR windings under VFTOs of different frequencies is obtained. The results show that, the voltage waveform in the SCSR windings more rapidly attenuates as the VFTO frequency increases. The peak value of the oscillating voltage in the high-voltage winding of the SCSR is higher than that in the low-voltage winding.

Partial discharge (PD) of high voltage equipment detected by online monitoring is regarded as a key indicator of insulation status. Threshold estimation exerts an important influence on the denoising effects of PD signals after wavelet-based denoising. In order to improve the adaptive performance of wavelet-based denoising and reduce the distortion of denoised signal, an approach of hybrid particle swarm optimization (HPSO) adaptive wavelet threshold estimation (HPSOTE) is presented in this paper. To obtain the global optimum thresholds, a novel hybrid particle swarm optimization algorithm merging crossover mutation and chaos is proposed in HPSOTE which could solve the premature convergence problem of common threshold selection methods. Genetic algorithm (GA) and particle swarm optimization (PSO) algorithm are adopted to compare the effects with HPSOTE. The denoising results of simulated and actual PD signals show that HPSOTE has a faster convergence rate and more effective global optimization ability than the others and significantly improves the credibility and calculation speed. It gives better mean square error (MSE) and amplitude error performance. This HPSOTE can remove the noise effectively and has comparatively high application value in PD online monitoring for smart grid based on big data.

There are typically large circulating current losses when such a current is produced in a gas-insulated switchgear (GIS). An excessive circulating current also causes a heating phenomenon and insulation aging, as well as hidden dangers and adverse effects on the normal operations of power systems. In addition, the installation of hybrid reactive power compensation (HRPC) may increase the complexity of the circulating current. Thus, a detailed investigation of GIS enclosure circulating current on an ultra-high-voltage (UHV) substation with HRPC is imperative. Here, the mechanism of the enclosure circulating current is thoroughly discussed, and models of the GIS busbar, and enclosure are established based on the partial element equivalent circuit (PEEC) method. Combined with HRPC equivalent circuit model, the equivalent calculation model for the GIS enclosure circulating current with HRPC equipment is established. The influence of the structural parameters on the circulating current, such as the inlet capacitance of the stepped controlled shunt reactor (SCSR), enclosure radius, enclosure height from the earth, and distance between earthing points, are considered in terms of the simulation model as built using transient simulation software. The factors that influence the enclosure circulating current and their associated rules are used to develop suppression measures.

The current paper aims to present a hybrid model for classifying faults in power transformers. The innovation of this paper can be shown by introducing a new method of data optimization based on the combination (subsets) of the set (C-set) method and the unsupervised fuzzy C-means (FCM) clustering algorithm. The new method aims to solve the quandaries of unbalanced data, outliers, and boundary ratios that exist in conventional and artificial methods. Considering the compactness of dissolved gas analysis (DGA) data, the C-set method is employed for dividing the data samples according to their fault types into multiple groups without repetition. The FCM algorithm is then adopted for the samples pre-selection process by obtaining the cluster centers of each C-set class. The obtained cluster centers are combined to form the labeled expert training data (LETD) set, which will train the 1-vs-1 multiclass support vector machine (MCSVM) with a linear kernel. The proposed model diagnosis obtained accuracy is 88.9%. Our proposed model has been compared with other soft computing and traditional models. The experimental results of this model revealed high performance in classifying transformer faults and improving the fault identification accuracy.

The application of hybrid reactive power compensation (HRPC) in ultra-high-voltage substations has a nonnegligible impact on the characteristics of transient ground potential rise (TGPR) in the gas-insulated switchgear (GIS) enclosure. In this paper, according to the principle of series compensation and stepped controlled shunt reactors under a very fast transient overvoltage, a simplified model of an HRPC device is established. Based on the generation mechanism of TGPR and the theory of transmission lines, the equivalent simulation circuit of GIS in a substation is designed under the occurrence of TGPR. Simulation experiments comparing the characteristics of TGPR with and without HRPC are conducted to explore the factors that influence TGPR. This paper proposes specific methods of reducing TGPR, and provides a theoretical basis for the construction of GIS protection devices for ultra-high-voltage substations.

This paper presents a theoretical study of the interrupting characteristics of circuit breakers in the event of phase-to-phase faults in UHV transmission lines with hybrid reactive power compensation (HRPC). The study uses the transmission line parameters of the Jindongnan–Nanyang–Jingmen UHV AC pilot demonstration project in China and establishes a simplified model for the distribution parameters of transmission lines. Mathematical expressions describing the relationships between circuit breaker interrupting parameters and compensation degrees of HRPC are derived. Based on these mathematical expressions and their comparisons with simulation results, the effects of HRPC on circuit breaker interrupting characteristics and on the parameters of the phase-to-phase fault circuit are determined, in which case the validity of the analytical method is verified. The results of this study will provide a theoretical foundation for practical implementation of HRPC in UHV transmission.

Permanent-Magnet-Biased Saturation Based Fault Current Limiter (PMFCL) may find early applications in high-voltage and large capacity power systems due to prominent advantages such as compactness, small size, reliable and safe operation, and zero reset time. The prevailing topologies and the operating principles of the PMFCLs are elucidated in the paper. Theoretical analysis on both the static and dynamic characteristics of different modes of PMFCLs is carried out comparatively, in which new concepts of effective magnetic flux density and magnetic field intensity are proposed to describe the overall impacts of the magnetic field on the current limiting capacity of the PMFCLs. Based on theoretical analysis and mathematical deduction, equivalent magnetic circuits and equations are established, which presents invaluable fundamentals for further study on the operating mechanism of different modes of PMFCLs as well as optimization of the fault current limiting topology design.