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.

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.

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.

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.

Polarimetric Fiber-optic current-sensing technology is typically employed for measuring high current, as the low Verdet constant of optical fiber makes Faraday rotation not noticeable in low-current measurements and subsequently leads to low current sensitivity. To enhance current sensitivity, a polarimetric method based on a reflective polarization-bias-added (RPBA) structure is presented in this paper. Firstly, it is proved by the Jones matrix that current sensitivity would be compromised due to the constant term in the traditional sensing output. Then, the single-axis measurement method is employed to eliminate the constant term using the single-axis working circulator. In consideration of the accuracy of subsequent signal decoding, the bias is generated by the RPBA structure to process optical signals between the circulator and the mirror. Next, a decoding algorithm based on parameter optimization is presented to restore the measured current from the photodetector output. Finally, the experimental results show that the current sensitivity of the presented method can be larger than 0.005 V/A under the premise of small measurement error in the vibration-and-temperature test. Compared with the existing polarimetric methods whose current sensitivity tends to be 0.002 V/A, the presented method has better current sensitivity without incurring additional sensor-head turns or optical devices.