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Transmission line (TL) models are widely used within the simulation of the very fast transient over-voltages (VFTO) for gas-insulated substations (GISs); however, due to quasi-TEM approximation and model complexity, energy losses related to bushing radiation and frequency-dependent soil parameters are either not available or simply neglected, limiting the simulation accuracy of TL models. In this study, a new frequency-domain TL model is proposed, enabling the model to consider the influences of both radiation and soil losses in a VFTO simulation. Derived from the radiation power of a line antenna model, the radiation resistance of a “lossy” TL is put forward as an equivalent of the radiation loss for GIS bushing. For the soil loss, the Sunde approximation formula and the L-S soil dispersion expression are involved, and the parameters of the overhead busbar are also analyzed. The model gets validation by the measured VFTO generated at a full-scale 1100 kV GIS testing circuit. By considering radiation loss to suppress high-frequency response and soil loss to improve low-frequency response accuracy, the calculated and measured waveforms have the best consistency, which may greatly help assess the risk of insulation breakdown and the level of very fast transient disturbance in GISs. [ABSTRACT FROM AUTHOR]

With the rapid development of semiconductor devices, researchers have proposed different types of high-frequency pulse voltage generators based on power electronic converters to meet the requirements of microorganism inactivation, water pollution purification, and piezoelectric and dielectric electroactive polymer drives. The transient modeling of these high-voltage converters aids in understanding the electrical characteristics of the devices and optimizing their performances. This article analyzes the electrical behavior of a semiconductor switching device (i.e., an insulated gate bipolar transistor) used during the switching transient of the converter and constructs an electromagnetic transient model of the flyback converter that considers both the parasitic elements and the ferromagnetic losses of the transformer. The accuracy of the proposed model is then verified by comparing calculation results obtained using the model with experimental measurement results. [ABSTRACT FROM AUTHOR]

Recently, 2-D multiple signal classification (MUSIC) algorithm was applied to map lighting propagation with improved quality. However, the quality is improved at the cost of increasing the calculation load. To improve the efficiency, this article proposes an improved MUSIC-based lightning mapping algorithm, which transforms the 2-D direction of arrival (DOA) estimation problem for an L-shaped array into 1-D DOA estimation problem for the two arms of the array. Additionally, the lightning mapping array is arranged in a nonuniform way to reduce the risk of trivial ambiguity problem. The performance of the developed lightning mapping system is verified with numerical Monte Carlo simulation and further with real lightning observation results. The simulation results show that the nonuniform array outperforms the uniform array in terms of detection accuracy, spatial resolution, and antiambiguity. The observation results show that the MUSIC-based methods produce better lightning mapping quality compared with the interferometry method (15 777 sources mapped), due to better robustness for low signal-to-noise ratio (SNR) lightning very high-frequency (VHF) signals. Compared with the 2-D MUSIC method (34 620 sources mapped), the proposed low computational cost method (30 461 sources mapped) is proven to produce fairly similar path of lightning leader with significant lower computational cost. Specifically, the proposed method saves about 84.91% of calculation time compared with the 2-D MUSIC method in practice. [ABSTRACT FROM AUTHOR]

Gas discharge tube (GDT) breaks down discharge with surge overvoltage during long-term use. Notably, there is a risk of short-circuit failure due to the drop in insulation resistance after a certain number of discharges, which might be mainly caused by cumulative discharge. This article builds a cumulative discharge experiment platform to analyze the failure mechanism, performed the GDT whole life cycle cumulative discharge experiment and focused on the change law of its insulation resistance and breakdown voltage. For samples that are short-circuited, X-ray observation and vibration testing perpendicular to the GDT axis are conducted to examine the internal micro-morphology without damaging their external structure. The GDT is opened and its internal structure and material properties of the GDT cavity are compared and analyzed by scanning electron microscope (SEM) and energy dispersive spectroscopy (EDS) methods. The results indicated that the insulation resistance of GDT continuously decreased by several orders of magnitude in the last 10% of the life cycle, and the insulation resistance before failure is generally less than 1 $\text{k}\Omega $. Through X-ray observation of the short-circuit failure sample, two different abnormal growth phenomena in the cavity are found, including flocs between the electrodes and deposits on the tube wall. Further analysis and experiments demonstrated that the flocs between the electrodes and the deposits on the tube wall are the primary factors causing the degradation of GDT insulation performance. The formation mechanism of the two short-circuit modes is explained by the difference in the splash angle and mode of metal particles of different sizes on the electrode surface. [ABSTRACT FROM AUTHOR]

SF 6 /N 2 mixtures is considered as a practical alternative proposal of SF 6 in GIS and GIL. Simulating particle transportations and chemical reactions during the positive streamer propagation in SF 6 /N 2 mixtures assists in the insulation performance optimization of SF 6 /N 2 mixtures. This paper presents a fluid dynamic model coupled with the chemical reaction system for the positive streamer propagation in SF 6 /N 2 mixtures. The Townsend coefficients of the 20%SF 6 /80%N 2 mixture derived from the proposed chemical reaction system are in accordance with the measurement results. Based on this model, the propagation of the positive streamer in a 1 mm needle-plate gap in the 20%SF 6 /80%N 2 mixture is simulated. Simulated results indicate that there exists a negative space charge region in the streamer channel. It can be attributed to the increasing attachment rates of SF 6 yielding SF 5 − and SF 6 −, and the reduction of the ionization rates of N 2 and SF 6 in the streamer channel. Besides, it is noted that the ionization activities of N 2 and SF 6 at the streamer head are equally important to support the continuous propagation of the positive streamer. The ionization of N 2 in the streamer channel serves as an important factor to supply electrons and avoid the accumulation of the negative space charge. [ABSTRACT FROM AUTHOR]

C 4 F 7 N/CO 2 is one of the most promising alternatives to SF 6 in high-voltage electrical equipment such as gas insulated switchgear (GIS) because of its excellent electrical performance and low environmental impact. However, the insulation characteristics of C 4 F 7 N/CO 2 is still unclear regarding the effect of conductor surface roughness. To obtain a figure of merit of C 4 F 7 N/CO 2 gas mixtures and to evaluate its sensitivity to local inhomogeneous electric field, the breakdown voltage of electronegative gas considering surface roughness is developed using the streamer discharge theory. A gas discharge experimental platform for C 4 F 7 N/CO 2 mixed gas is set up and the discharge test is carried out under gas pressures from 0.15∼0.5 MPa having a maximum protrusion height of 15 μm. The results demonstrate that when the volume fraction of C 4 F 7 N is 10%, the figure of merit of C 4 F 7 N/CO 2 mixture is slightly higher than that of SF 6 gas. Therefore, at the same pressure, the standard of conductor surface roughness for C 4 F 7 N/CO 2 equipment can refer to the original SF 6 gas equipment. [ABSTRACT FROM AUTHOR]

Large-capacity capacitor banks have been used to control the reactive power of ultra high voltage ac grid in China. The high switching inrush current of SF6 circuit breakers used for large-capacity capacitor banks has caused great mechanical wear after arc ablation, which leads to the serious erosion of the arcing contacts of the circuit breakers, thus shortening the electrical life. To improve the electrical life of circuit breakers, the wear mechanism and mass loss characteristic of arcing contacts in the making process were studied in this paper. Through erosion experiments in the making process and arc ablation experiments in the circuit breaker test device, the wear mechanism and the mass loss characteristics were analyzed via the detection of worn contacts and wear theory. At normal temperature, the wear mechanism is mainly abrasive wear. At high temperature, the wear mechanisms in three stages mainly include adhesive and abrasive wears. When the closing inrush current amplitudes are 10, 20, and 30 kA, the mass loss of mechanical wear is greater than that of arcing ablation. The total mass loss and mass loss rate per unit charge increase with the interference radius between two contacts and with test current. However, with current amplitude higher than 20 kA, the total mass loss rate decreases. Suggestions to reduce wear are proposed to improve the electrical life of circuit breakers. [ABSTRACT FROM AUTHOR]

In allusion to the particle movement control and the removal of particles in gas insulated metal-enclosed transmission lines (GIL) in a non-uniform electric field, a test analysis platform was set up in this paper. Via the platform established, the metal particles movement between electrodes and the spark electrodes discharge process were studied. Further, forces that act on the particle were analyzed, and a particle movement simulation model was established. Based on the experiment and simulation results the particle moving and distributing characteristics were discussed. The result shows that breakdown usually took place when the particles are moving near to the high voltage electrode whose process is intermittent. The particle moving trajectory is stable between the sphere-plate electrodes, and the trajectory range narrows when the sphere diameter decreases. Moreover, when discharge occurs, the trajectory range decreases. [ABSTRACT FROM AUTHOR]

The overhead catenary system of high-speed railway, usually supported by viaducts, attracts more direct strikes than the conventional railway. However, there are ten thousands of slender steel rods in the reinforced concrete structure of viaducts. Therefore, it takes a lot of time to calculate the model of a long series of viaducts by the conventional electromagnetic field modeling method. An electromagnetic transient model for high-speed railway viaducts struck by lightning based on the decoupling method is proposed in this paper, in which the railway viaducts are divided into the box girder unit and viaduct pier unit. The viaducts model based on decoupling method (VMDM) is established by a series of box units supported by viaduct pier units at equal intervals. The equivalent circuit model of each unit was obtained by employing the vector fitting method based on the frequency-domain response. Experimental results of a newly built railway viaduct pier under lightning impulse current were presented to validate the equivalent circuit model of viaduct pier unit, which show high consistency with simulation results. In particular, the typical VMDM model of Beijing-Tianjin intercity railway viaducts was established with the proposed method. The result obtained from the VMDM model are compared with the simplified model. [ABSTRACT FROM PUBLISHER]