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In this article, the dissipation of predeposited surface charges on the SiC/epoxy coated insulator is investigated. Similar to Part I of this study, the analysis is carried out for the system of a pair of finger-shaped metallic electrodes placed on flat material samples and different types of material precharging are considered. Specifically, two cases based on different types of electrode–sample contacts (Cases 1 and 2, similar to Part I) are examined as well as surface charging by external corona (Case 3). It is shown that surface charge dissipation in Cases 1 and 2 takes place in two stages, whereas three stages in the charge decay process are identified in Case 3. It is shown that the rate of charge dissipation is strongly affected by the increase of the content of SiC filler in the coating material. The experimental results obtained for different cases are compared and discussed by employing results of the calculations of the electric field in the experimental setups and surface conductivities and surface trap characteristics obtained in Part I. [ABSTRACT FROM AUTHOR]

Surface charge accumulation on silicon carbide (SiC)/epoxy coatings with different contents of SiC filler, 3, 5, 7, and 10 wt%, is investigated using flat samples of epoxy substrate. In the experiments, a pair of finger-shaped electrodes was attached to the sample’s surface using direct pressing and conductive adhesive providing two different types of contacts and, respectively, surface charging methods. The electrodes were energized by applying dc voltage for various time intervals and resulted surface charge distributions between the electrodes were measured. It was found that depending on the contact type, charging duration, and filler content, different patterns of homocharge or heterocharge appeared on the material surface. Physical reasons for the observed effects are analyzed based on the calculated electric field distributions in the experimental setup, results of the auxiliary tests on material charging in a limited air volume, and surface trap energy distributions measured by utilizing the isothermal surface potential decay (ISPD) method. Application of SiC/epoxy coating for controlling surface charge accumulation is discussed. [ABSTRACT FROM AUTHOR]

In this paper, an electro-thermal based surface charge accumulation model is established. Heat conduction, heat convection and heat radiation are included. The gas flow is coupled with fluid equations to describe the motion of charge carriers, and gas current density is also corrected by the gas velocity. In terms of it, the surface charge and electric field on a basin-type insulator in vertical laid DC gas insulated switchgear (GIS) and gas insulated transmission line (GIL) under different temperatures and pressures are studied. The results show that a temperature gradient is formed in the gas from top to bottom in the vertical direction, and the increase in pressure leads to a higher temperature of the lower surface. The surface charge density and tangential electric field increase with the temperature and decrease with the pressure. As a comparison, the surface charge and tangential electric field are calculated without considering temperature and without considering heat convection. The former leads to a lower tangential electric field than this model, while the latter brings about a higher electric field. This paper provides a more accurate reference for the design of DC GIS/GIL through a more comprehensive model. [ABSTRACT FROM AUTHOR]

In this paper, a liquid circulation system is constructed whereby gas bubble dynamics and electrical signal evolution preceding the oil gap breakdown are registered in stationary and flowing transformer oil. Based on a number of repetitive tests, two types of breakdown are classified: one takes place after bubble growth and originates in the bubble or the mixture of liquid and gas when the applied voltage is in the negative half-cycle; the other follows streamers resulting from the protrusion of bubble tip in the positive half-cycle. For each type of breakdown, partial discharge (PD) pulse is captured preceding the breakdown. As the oil flow rate varies, bubble dynamics change but the characteristics of each breakdown remain. In addition, it is found that oil breakdown voltage is improved as the flow rate increases. In terms of PD occurrence and bubble growth, the role of gas bubble in oil breakdown initiation, as well as the effect of oil flow on breakdown, is discussed. [ABSTRACT FROM AUTHOR]

In electrical engineering, partial discharge (PD) measurement is frequently employed to detect insulation defects and judge insulation conditions of high-voltage electrical apparatus. However, it is easily corrupted by white noises in the field. In this article, a joint algorithm is proposed, in which the wavelet threshold and total variation (TV) denoising methods are combined by the convex optimization theory to denoise ultrahigh frequency (UHF) PD signals corrupted by white noises. Since the two respective methods are incorporated into the joint algorithm, it is with high potential to reduce oscillation error introduced by the wavelet threshold method and eliminate stair error introduced by the TV denoising method. In order to validate the effect of the proposed algorithm, a numerical simulation is carried out to compare it with several existing methods. Indicators of their performance are computed, and the results verify that the proposed algorithm outperforms all the other methods. [ABSTRACT FROM AUTHOR]

Partial discharge (PD) taking place in a solid dielectric-bounded cavity involves physical processes such as free electron supply, discharge development and surface charge decaying, which bring about memory effects and become the main reasons for stochastic behavior of PDs. This paper reviews numerical modeling of cavity PD in the past 30 years. In the first place, physical processes relevant to PD activity are summarized, and modeling methods for discharge development are classified. Then some differences of PD modeling at AC and DC voltages are distinguished. Subsequently, reproducing methods from simulations to experiments are introduced, as well as their comparison under different conditions and with the emphasis on voltage frequency and PD aging. At last, some problems about current simulation models are discussed, and our suggestions for future work are proposed. [ABSTRACT FROM AUTHOR]