Xingming Bian

Construction of three-dimensional graphene interfaces into carbon fiber textiles for increasing deposition of nickel nanoparticles: flexible hierarchical magnetic textile composites for strong electromagnetic shielding

Since manipulating electromagnetic waves with electromagnetic active materials for environmental and electric engineering is a significant task, here a novel prototype is reported by introducing reduced graphene oxide (RGO) interfaces in carbon fiber (CF) networks for a hierarchical carbon fiber/reduced graphene oxide/nickel (CF-RGO-Ni) composite textile. Upon charaterizations of the microscopic morphologies, electrical and magnetic properties, the presence of three-dimensional RGO interfaces and bifunctional nickel nanoparticles substantially influences the related physical properties in the resulting hierarchical composite textiles. Eletromagnetic interference (EMI) shielding performance suggests that the hierarchical composite textiles hold a strong shielding effectiveness greater than 61 dB, showing greater advantages than conventional polymeric and foamy shielding composites. As a polymer-free lightweight structure, flexible CF-RGO-Ni composites of all electromagnetic active components offer unique understanding of the multi-scale and multiple mechanisms in electromagnetic energy consumption. Such a novel prototype of shielding structures along with convenient technology highlight a strategy to achieve high-performance EMI shielding, coupled with a universal approach for preparing advanced lightweight composites with graphene interfaces.

Comparison between the audible noises generated from single corona source under DC and AC corona discharge

The corona-generated audible noise (AN) factor is an important consideration in the design and operation of ultrahigh voltage direct current (DC) and alternate current (AC) transmission lines. Due to the differences in discharge process and corona-generated space charges between the DC and AC corona discharge, the audible noise from DC and AC corona has different characteristics. This paper conducts a series of experiments by measuring the time-domain waveforms of the audible noise from a single corona source under DC and AC voltage. Sound pressure pulses are extracted from a correlation analysis, and then a detailed comparison of the basic characteristics of DC and AC corona-generated AN in time-domain and frequency spectrum is given. Results from this paper stand to contribute to an explanation of existing results in AN measurement and analysis from DC and AC transmission lines.

The effect of surface roughness on corona-generated electromagnetic interference for long-term operating conductors

This paper presents a research of the surface roughness effects on corona-generated electromagnetic interference of long-term operating conductors. The detailed surface morphologies and roughness of typical long-term operating conductors were measured and analyzed. The radio noise measurement system based on the corona cage was discussed and the actual radio noise generated by the conductor in the measured cage was obtained, based on the parameters of the corona cage and the measured data. The radio noise tests were carried out under both dry and wet conditions. Under two types of conditions, the corona intensity was higher on the long-term operating conductors contrasted to the new conductors as a result of the anomalistic surfaces of the long-term operating conductors. The rate of decrease of corona inception voltages between the long-term operating conductors and new conductors was discovered to increase with the raise of surface roughness degree Ra in linear relationship. Approximate linear relation was also discovered between the averaged radio noise deviation and Ra. The rate of decrease of corona inception voltages under wet conditions was slightly higher (about 1%) than that under dry conditions. The difference between the radio noise of long-term operating conductors and that of new conductors was larger (1.3 dB) under wet conditions compared to dry conditions.

Designing high-performance electromagnetic wave absorption materials based on polymeric graphene-based dielectric composites: from fabrication technology to periodic pattern design

Since the development of advanced electromagnetic absorption materials is highly critical in telecommunication and stealth technology, both fabrication technology and structure design are significant in achieving broadband and strong absorption performance. For understanding the effects of fabrication technology and structure design on performance, in this work two fabrication methods, including the traditional mixing and novel framework method, are demonstrated to investigate the dispersion capability of reduced graphene oxide in polymeric matrices. Moreover, artificial structure designs, including the layers of unit cells, top-layer shape and top-layer materials, are used for further optimizing the microwave absorption performance. A performance comparison suggests that fabrication via framework technology is more favorable to obtain an ideal impedance match in the composites. Additionally, the meta-structural design coupled with the related mechanism for substantially broadening the absorption bandwidth has been systematically discussed. The results imply that the combination of fabrication technology and periodic pattern design provides a promising platform for achieving high-performance absorption materials.

Statistical characteristic in time-domain of direct current corona-generated audible noise from conductor in corona cage

The corona-generated audible noise (AN) has become one of decisive factors in the design of high voltage direct current (HVDC) transmission lines. The AN from transmission lines can be attributed to sound pressure pulses which are generated by the multiple corona sources formed on the conductor, i.e., transmission lines. In this paper, a detailed time-domain characteristics of the sound pressure pulses, which are generated by the DC corona discharges formed over the surfaces of a stranded conductors, are investigated systematically in a laboratory settings using a corona cage structure. The amplitude of sound pressure pulse and its time intervals are extracted by observing a direct correlation between corona current pulses and corona-generated sound pressure pulses. Based on the statistical characteristics, a stochastic model is presented for simulating the sound pressure pulses due to DC corona discharges occurring on conductors. The proposed stochastic model is validated by comparing the calculated and ...

Measurement method of ionic mobilities in direct current corona discharge in air

Ionic mobilities are characteristic parameters for describing the motion of charges in electric field and also basic parameters for the calculation of ionized field and ion current density of ultra high voltage direct current (UHVDC) transmission lines. This paper presents a measurement method of ionic mobilities in air. The analytical solution of ion mobility was derived from the equations of the ionized field and the ion current density. A circular parallel plate apparatus was applied to measure the ionic mobilities. Experimental results show that in direct current corona discharge of room temperature, the measured result of negative ion mobility was 2.23 to 2.51 ×10^-4 m²·V^-1 s^-1, and the average value was 2.39 ×10^-4 m²-V^-1·s^-1; the measurement of positive ion mobility was 1.54 to 1.93 × 10^-4m^2·V^-1·s^-1, with the average of 1.71 × 10^-4 m^2·V^-1·s^-1.

Application of signal sparse decomposition in the detection of partial discharge by ultrasonic array method

The detection of partial discharge of power transformer is important for the safe operation of a power system. The direction of arrival is an important part of ultrasonic array detection. Classic DOA estimation algorithms based on subspace analysis do not perform well under the conditions of low SNR and small snapshot numbers. The problem with using an improved algorithm is that it requires a huge amount of calculation. In this paper sparse signal decomposition is applied to spatial spectrum estimation. The authors derived the model of array signal direction finding by the use of matching pursuit algorithm, setting up overcomplete dictionaries for different types of sensor array and simulating different types of sensor array receiving signals. Simulations and experiments show that direction finding based on MP decomposition method performs better than using the MUSIC algorithm under the conditions of low SNR and small snapshot numbers, and that the influence of array types is less.

Corona characteristics of HVDC conductors with different surface conditions obtained in a controllable accelerating contamination depositing apparatus

Suspended aerosols in the vicinity of discharged HVDC transmission lines will be charged by ions and deposit on the surface of the conductors. In order to obtain the conductors with different contamination conditions, a controllable accelerating contamination depositing method by introducing a controllable ionized field is proposed in the present paper. The conductor samples contaminated by 3 typical patterns were prepared and the morphology of the conductor surfaces was characterized by scanning electron microscopy (SEM). The photon counting rate of the conductors and the electric field strength on the ground electrode were also tested. The anticipatory contamination depositing results were obtained, specifically, the surface conditions of the conductors could be improved or deteriorated, therefore, the corona discharge could be suppressed or enhanced in corresponding patterns of the proposed contamination depositing method.

3D full maxwell research for effect of initial electromagnetic field on very fast transient overvoltage in GIS

Very fast transient overvoltage (VFTO) generated by operating disconnect in gas insulated substations has great concern in high voltage rated substation. Because many effecting factors, including structure parameters and charge distribution, can be integrated into analysis of 3-D electromagnetic finite element method (FEM), this method is regarded as accurate method. VFTOs were analyzed based on electromagnetic FEM method with not only considering the structure of conductors and contacts but also considering the non-uniformity of initial electric field around the conductors at initial time. From simulation results we can see that VFTOs simulated by field based model were larger than that by electromagnetic transient program (EMTP) and the VFTOs by field method advance that by EMTP in time even through ratio of diameter to length is smaller. Comparisons of simulation results were made between circuit-based model and field-based model. The discussions about the key points for the use of field-based model were taken. For larger ratio of diameter to length in compact GIS the magnitude of simulated VFTOs is significantly affected by analysis methods. This field based analysis method will be used in research of phase-selection to suppress the VFTO, in modeling of arcing channel and in obtaining equivalent impedance of source line in GIS.

The features of positive dc corona discharge on the surface of the conductor with different contaminations

HVDC transmission lines operating in polluted areas may absorb a large amount of contamination, which seriously affects the corona discharge and its associated audible noise, electric field, ion current density from the transmission lines. To fully study the effects of conductor surface condition on photon count and dc electric field, conductors coated with different kinds of contamination were investigated and compared with a clean one. Scanning electron microscopy (SEM), energy-dispersive X-ray (EDX) analysis and SPIP were employed to characterize the surface morphology of the conductor samples. To fully study the effects of conductor surface condition on photon count and dc electric field, conductors coated with different kinds of contamination were investigated and compared with a clean one. Kaolin, salt and carbon were used as the coating contamination during the experiment. Experimental results illustrated by both ultraviolet photographs and measurement data reveal the dielectric coating resists corona discharge and enhances the onset voltage when the contamination is uniform enough, while electrical conductive contaminations have less impact when the coating is uniform enough.