Dianchun Zheng

About interior insulating design and rectifying of the 35kV power cable joints

The qualities of power cables joints play a crucial part in electrical systems providing high safety and reliability electricity power for consumers, and 35kV prefabricated cable joints up to now are popular products, so their interior insulating design principles, electric field distributions and dielectric coordination are in details represented in this paper, especially, using the finite element method for rectifying the joint structures, modifying stress cone profiles, furthermore, the calculating programs are created and the useful results are given.

Wavelet transform denoise of PD signal on coaxial cylinder electrodes

The paper presents the basic principle and method of dealing with PD (partial discharge) signals using wavelet transform. It is demonstrated that wavelet transform is a useful and effective tool for extracting PD pulse signals from noise. It makes more certain that failures caused by the PD which happens in the GIS, GIC and GIL, could be precisely measured, predicted and monitored.

Analysis of PD spectrums in high voltage apparatus insulated with compressed gas

The paper presents a set of the curves about PD spectrums in the high voltage apparatus insulated with compressed air gas in the different pressures, which are measured with the UHF method. The aims of the research work are to reveal the essence characteristics of the compressed gas PD. To carry out the research work, the experimental models are designed according to the typical structures of the high voltage apparatus insulated with the compressed air gas. The PD phenomena are appeared absolutely on the spaces between the electrodes because the failures brings about when the insulating weak existing, for example, a free metallic particle can attracted to the HV conductor and produce micro-discharge that triggers breakdown. Other causes of failure are discharges from any stress-raising protrusion, capacitive sparking from an electrode which is not properly bonded to either the HV conductor or ground, and so on; and the common feature of all these defects is that they generate PD activity in advance or complete breakdown. The research results are necessary for detecting failures on the high voltage apparatus insulated with compressed air gas and have practical significance.

Endurance behavior of the SF/sub 6//N/sub 2/ mixtures experiment under AC and impulse voltages

The aims are to develop new kinds of insulating mediums being technically as well as economically attractive and fully understand the electronegative gas characteristic of endurance voltages, mechanism of partial discharge and widen their using areas in the high voltage system experiments. The article presents the experiment procedures, contents are involved in as follow: point-plane, point-point, co-axial cylindrical and co-centric sphere electrode systems, and industrial purity SF/sub 6/ and its mixture combining N/sub 2/ are filled into the experiment chamber in different partial pressure and applied the AC and impulse voltages in different pressures. The mechanism of initiated PD potentials and breakdown of the SF/sub 6/ and SF/sub 6//N/sub 2/ have been analyzed theoretically according to the molecular structure and physical characteristics of the electro-negative vases, the research works are helpful to develop and widen using fields of the SF/sub 6/ and its mixtures in high voltage engineering.

Metallic particle effect on the gas PD in co-axial cylinder electrodes

High voltage apparatus, for example GIS, insulated in a gas dielectric easily show partial discharge (in short PD), because of particle impurities, particularly some kinds of metallic particles. The PD failures are very dangerous and detrimental, because they could destroy the insulating system of the high voltage apparatus, result in a great deal of economic damage and imperil personal safety. Co-axial cylinder electrodes have been made to simulate the high voltage apparatus structure and service conditions under various applied voltages and existence of some types of metallic particles of different materials (for instance, copper, stainless steel, steel) with variable diameters, lengths and geometry. Through practical experiments in the laboratory, the relationships between PD inception voltage, PD quantities, length, materials and geometry have been obtained. Meanwhile the PD signals have been recorded by the measurement systems. The position of the particles shows different waveform and behavior, so that it could provide a way to detect the PD failure characteristics, location and attribution, and help to analyze, judge and assess the service conditions.

Dynamic behaviors of SF 6 discharge process in short parallel-plate gaps

The two-dimensional hydrodynamic discharge model is presented based on the hydrodynamic mechanics theory and gas discharge characteristics, with a uniform applied field, during the discharge process of SF6 at atmospheric pressure, and it is established by adopting Poisson equation in conjunction with the continuity equations for electrons, negative and positive ions, besides, the photo - ionization is also considered in the proposed model. The Finite Difference-Flux Corrected Transport technique is used in numerical simulation of discharge process, in order to improve the accuracy and efficiency. Then the gap-space electric field distribution, space ions distribution are revealed from the microscopic mechanism, and the evolutions of the charged particles are obtained in detail, furthermore, the tempo-spatial critical point of the avalanche-to-streamer in this model is discovered, the influence of applied voltage and initial plasma charge density on the streamer characteristic are also investigated. The results show that the initial plasma charge density is closely related to the gradient slope of the gap-space electric field distribution and electron density distribution, meanwhile, the electric field strength, the propagation velocity and charge density of the streamer head increase with increasing applied voltage. Above results analysis can be in favor of further study of the discharge mechanism and provide the theoretical support for electrical equipment designed.

Dynamic behaviors of barrier discharge in air-dielectric at atmospheric pressure

With the purpose of study air-gap discharge phenomena at atmospheric pressure and deeply understanding behavior of barrier discharge in air-dielectric, the one dimensional and self-consistent fluid model of the gas discharge is established based on the electron and ion continuity and momentum transfer equations coupled to Poissons equation, then the micro discharge progress of the air-dielectric and its influence of the surface charge accumulation on dielectric barriers under alternating voltage are analyzed and demonstrated in detail. The models of numerical simulations of dielectric barrier discharges of a plane-parallel electrode arrangement covered with solid dielectric and comprising an air gap are made up, and the results of simulation are obtained for the case when the applied field in the gas exceeds its breakdown threshold and discharge current pulses can be formed, i.e. charge transfer in the gas phase takes place in the form of an electron avalanche discharge, simultaneously, the facts were found that the temporal and spatial distributions of the electric field, electron density and the ion density obtained in the electron avalanche discharge at atmospheric pressure could improve the air-gap discharge performance, furthermore, the calculated discharge current patterns are found to agree structurally and also to correctly display the predicted avalanche.

Dynamic behaviours on discharge process of SF 6 -N 2 mixtures in short gap with parallel-plane electrodes

The purpose of this research work is to reveal dynamic behaviors of particles, such as electron, positive ion, negative ion, which are produced, augmented, attached, recombined, including their drafting and diffusing under electric field, during the discharge process of SF6-N2 gas mixtures, and also to discover the discharge disciplinarian in micro-mechanism for reasonably utilizing the SF6. The fluid model of SF6-N2 mixtures gas discharge is established by adopting particles continuity equation together with coupling Poisson equations. This model is composed of the electrons, positive ions and negative ions continuity equations coupled with the Poisson equation. Two-dimensional simulation of the streamer discharge in SF6-N2 gas mixtures, which contains 50%SF6, is studied in this paper. A program based on the finite element method in its full two-dimension form is developed and employed for the solution of transport equations of charged species under the effect of space-charge electric field. Results of two-dimensional simulation of cylindrically symmetric streamer between parallel-plane electrodes are presented. The formation and propagation of streamer in numerically was observed. The space electric field distribution, space ions distribution and drift velocity were predicted by the model. Through the above results Analysis can help to more profoundly understand streamer discharge mechanisms and provide the theoretical support for electrical equipment designed.

Experimental research on endurance behaviors of the SF 6 /N 2 mixtures under impulse voltage

The aims are to develop new kinds of insulating mediums being technically as well as economically attractive and fully understand the electronegative gas characteristic of endurance voltages, mechanism of partial discharge and widen their using areas in the high voltage system. The article presents the experiment procedures, contents are involved in as follow: needle-needle, needle-plane, sphere-plane, sphere-sphere and needle-sphere electrode systems, and industrial purity SF6 and its mixture combining N2 are filled into the experiment chamber in different partial pressure and applied the impulse voltages in different pressures. The mechanism of initiated PD potentials and breakdown of the SF6 and SF6/N2 have been analyzed theoretically according to the molecular structure and physical characteristics of the electro-negative gases, the research works are helpful to develop and widen using fields of the SF6 and its mixtures in high voltage engineering.

Dynamic behaviors of the streamer development and propagation in SF 6

SF6 gas is an important insulated medium and is wildly used in electric power industry for gas-insulated equipment; this paper aims to deeply understand the streamer discharge mechanism in SF6, and to better use of SF6 gas in the electrical equipment. The two dimensional and self-consistent fluid model of the gas discharge is established based on the electron and ions continuity transfer equations coupled to Poissons equation, furthermore including the model of photoionization. To overcome the problem about enormous calculation required of photoionization, some simplified methods are implemented in this paper. In simulation, the particle flux-continuity equations is solved by the flux corrected transport technique (FCT), and the iterative symmetric successive over-relaxation (SOR) method is used to solve the coupling Poissons equation. Results of two-dimensional simulation of cylindrically symmetric streamer in SF6 between parallel-plane electrodes are obtained. We present and discuss conclusions about streamer transport based on the results of these studies. The temporal and spatial transformation of charged particle densities, electric field strength, discharge current and discharge propagation velocity during the progression of discharges are investigated and the results indicated that, the processes of discharge have three phases: avalanche phase, streamer formation phase and streamer propagation phase. In addition, by comparing the results of simulation with and without photoionization process can be seen that the photoionization offers a large number second electron, and is absolutely necessary during the streamer propagation phase, which accelerates the velocity of the streamer propagation.