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This article investigates into signal regularity in ac series arc fault (SAF) detection. The regularity can solve the vital problem that SAF current characteristics change or disappear in unknown multiload circuits. A coupling method is adopted to capture high-frequency differential signals. The coupling signals show that the waveform in single-load circuits closely resembles the waveform in multiload ones. However, the coupling method confuses normal signals with arcing ones in dimmer loads. To address the issue, this article presents a time-series reconstruction method based on spectral features. First, the spectral features are analyzed between fault-like signals and fault signals. According to the spectral features and the desirable margin, the time series is self-adaptively decomposed and reconstructed. Then, the pulse-recognition algorithm is used to extract arcing features of the reconstructed signals. Finally, the detection method determined by single-load circuits is used to identify SAFs in unknown multiload ones. The results show the presented approach has good generalization performance and identification precision under arbitrary circuits. [ABSTRACT FROM AUTHOR]

The spatial–temporal distribution of reactive oxygen species (ROS) in human tissue is critical for the medical applications of cold plasma jet as it reflects the therapeutic range of cold plasma jet, but the mechanism for its formation is still unclear. To this end, KI-starch reagent was used to visualize the surface distributions of ROS on the model human tissues treated by a He + O2 plasma jet in this paper. It was found that the surface distribution of ROS was divided into two parts by a small donut-shaped of un-colored area. This un-colored area was resulted from the color fading of the model tissue, which might be induced by the AC electric field of the plasma jet and the plasma-generated reductive species. The colored area and the un-colored area had different trends with the working gas flow rate and the model tissue conductivity. The un-colored area increased with the expansion of the plasma plume and shrank with the increasing model tissue conductivity. [ABSTRACT FROM AUTHOR]

Breakdown voltage of hybrid gas-solid insulation system may greatly fluctuate due to the complex discharge processes, and the relationship between the breakdown voltage and the breakdown path is not clear. This paper studies the fluctuation of the breakdown voltage and the dispersion of the breakdown path. The results indicate that when the barrier is close to the high-voltage electrode, the breakdown voltage fluctuation is significant, and the significance rises with the increase of the barrier size. The breakdown paths are divided into two types, the probabilities of which are related to the barrier position, and the average breakdown voltages of the two path types are approximate. Under 50 Hz alternating voltage, residual charges have a significant effect on the direction of the breakdown path and have little effect on the breakdown voltage. The breakdown voltage fluctuates significantly when the breakdown path is long. It is found that the low atmospheric absolute humidity is another reason for the breakdown voltage fluctuation. [ABSTRACT FROM AUTHOR]

This paper proposes a new assessment method for lightning trip‐out of transmission lines that includes an improved analytic hierarchy process (IAHP) algorithm based on a lift in association rules. First, the k‐means clustering algorithm is used to discretize the geomorphic information along transmission lines, and ten feature factors are obtained. Next, by analysing the correlation between each feature factor and a lightning trip‐out event using the lift algorithm, the strong correlation factors are extracted. On this basis, an IAHP algorithm optimized by lift is proposed to establish an objective judgment matrix. Then, multiple indexes are combined as a criterion layer of the IAHP, and a lightning risk assessment model of transmission lines is established. Finally, the proposed method is validated by simulations using 28 transmission lines with 220 kV voltage grade of a provincial power grid of China. An assessment model is established using the lightning trip‐out data in the period 2010–2014, and then this model is employed to estimate the lightning trip‐out risk in the period 2015–2018. Based on the number of phase faults, the agreement between the estimation results and the actual values is 76%. The proposed model provides a new method for the lightning risk assessment of transmission lines. [ABSTRACT FROM AUTHOR]

Polypropylene (PP)-based polymers are environmentally friendly and degradable materials that make them attractive alternatives to polyethylene for the electrical insulation systems of power cables in the future. To enhance the insulation performance of PP and to impede leakage currents through the material, different admixtures are utilized. In this paper, the effect of nano-fillers on charge transport characteristics in PP composites under DC electric fields is investigated by using a bipolar charge transport model accounting for mobile and trapped electrons and holes as well as ionic species. The model was validated by comparing the numerical results with the experimental data. The dynamic distributions of space charge densities and electric field in PP with and without nano-fillers are analyzed and compared. The numerical results confirmed that 0.5 phr ZnO nano-fillers can significantly improve the electric field distribution in PP nanocomposites and suppress the bulk current by reducing the charge generation rate and mobilities of charge carriers, thus resulting in a decrease in the volume conductivity. The obtained results provide a theoretical background for tailoring PP-based composites for specific applications by controlling nano-fillers. [ABSTRACT FROM AUTHOR]

Due to a lack of high and stable power supplies for large-scale online monitoring devices, the intelligent development of high voltage transmission lines has always been restricted. This paper presents a method for capacitive power tapping from an insulated shield wire of overhead high voltage transmission lines with tuning. A general equivalent model, which considers the influence of line sag and landform on the equivalent circuit parameters, is established. The calculated equivalent circuit parameters show good agreement with the field measured data obtained by a 220 kV single-circuit transmission line. In order to maximize the tap-off power, a nonlinear tuning method is proposed since linear tuning can cause an overvoltage problem, and a tuned reactor is developed. Based on the measured equivalent circuit parameters, an experiment platform is built in the laboratory to measure the tap-off power under different resistive loads. The experimental results indicate that the maximum power is about 900 W, which represents an improvement of 80% compared with the maximum power without tuning. Additionally, the tuned reactor shows good robustness to the perturbation of equivalent circuit parameters, which validates the effectiveness of the proposed power tapping method. [ABSTRACT FROM AUTHOR]

Nutation reducers have recently attracted increasing attention, as they are used in important components of industrial robot joints. A novel disk-type nutation magnetic drive (NMD), based on the nutation gearing principle, is proposed in this article. Subsequently, a 3-D method for analyzing the magnetic field and predicting the torque of the disk-type NMD is presented. The 3-D analytical formula of the disk-type NMD is established on the basis of the equivalent current theory of permanent magnet, which is verified by the finite-element approach. Optimization design of the disk-type NMD is also carried out by applying the genetic algorithm. The results provide a reference for the design and optimization of the magnetic gears. [ABSTRACT FROM AUTHOR]

In order to improve the insulating performance of air-insulated high voltage electrical apparatuses, solid barriers are always introduced in the interelectrode gaps. The breakdown paths and conditions of air-insulated rod-plane gaps in the range of 2–5 cm under alternating voltages were investigated for three different sizes of polyvinyl chloride barriers inserted at different gap positions. The breakdown processes were observed using two cameras placed in orthogonal directions, and two typical breakdown paths were captured. The statistical results showed that the occurrence probabilities of the two typical breakdown paths were related to the barrier position, but that the breakdown voltages were very similar in all breakdown events. Further, formulae to predict the breakdown voltage were deduced using a linear regression method. The results provide a reference for improving the insulation performance of gas–solid hybrid insulation systems based on the barrier effect as well as for modelling gas discharges in hybrid gaps. [ABSTRACT FROM AUTHOR]

This paper presents a numerical model for the inception of positive dc corona discharges in air near cylindrical anodes, which plays a bridge role between the classic positive corona onset criterion and the photoionization model considering the effective radiation wavelength. The predicted onset voltages agree well with Peek's experimental data in a wide range of conductor radii and relative air densities. The influence of the collisional quenching of emitting excited states on the surface onset field is significant with low air density or small conductor radius. Within the effective radiation wavelength, numerical expressions for the photon absorption coefficient in air and Townsend's second coefficient due to photoionization are deduced on the basis of the new model. A different perspective on the classic coefficients is given. [ABSTRACT FROM AUTHOR]

The surface electric field (SEF) for the quasi-static negative corona discharge in atmospheric pressure air is investigated by the general fluid model which contains the continuity equations of electrons, positive ions, and negative ions coupled with Gauss' equation, considering the secondary electron emission. The SEF for the monopolar ion flow, which assumes that the whole interelectrode gap is filled with monopolar ions, is also investigated by the simplified model under the same boundary conditions at the anode. The results predict that the SEF remains constant at the onset value for both the negative corona plasma and the monopolar ion flow under a low corona current. With the increase of the corona current, the SEF is slightly strengthened for the negative corona plasma and significantly weakened for the monopolar ion flow in a wide range of conductor radii. The results for the monopolar ion flow are consistent with those deduced from the experimental data in the literature. [ABSTRACT FROM AUTHOR]

Photoemission replenishment criterion (PRC) is widely used to evaluate the onset conditions for negative corona discharges in atmospheric air. The relationship between the PRC and the air density is built up in this paper, which is validated for a wide range of electrode radii and low air densities. The total effective region responsible for photoemission is taken into account and a new geometric parameter that characterizes the photon absorption in the discharge volume is proposed, although the modification insignificantly affects the results. The numerical results agree well with Peek's experimental data for negative corona discharges in air, which are also consistent with Peek's formula for coaxial cylinders and Whitehead's formula for negative corona onset. [ABSTRACT FROM AUTHOR]