The Influence Of Metal Particles Geometric Dimensions On SF₆ Decomposition Characteristics Under Direct Current Partial Discharge

The sulfur hexafluoride?SF₆?gas insulated equipment,represented by the wall bushing,has been widely used in the power grids for its outstanding advantages,such as small footprint,high reliability and excellent electromagnetic environment.At the same time,with the construction of ultra high voltage direct current?UHVDC?power transmission project and offshore large-scale wind power transmission project,DC SF₆gas insulated equipment is bound to have a huge application prospect.Similar to AC gas insulated equipment,the internal of DC equipment also inevitably exists metal particles,and the usual insulation defects of metal particle are the wire-type particles,lamellar particles and granular particles?powder,nearly spherical?,greatly threatens the insulation system by distorting the electric field and inducing partial discharge?PD?in insulated equipment,and easily leads to accidents if not handled timely.The method of SF₆ gas insulated equipment condition monitoring and fault diagnosis,based on decomposed component analysis?DCA?,considers the volume fraction and the effective formation rates of SF₆ characteristic decomposition components have the close relation with the severity of PD and types of insulation defect which has such advantages as immunity from the effects of electromagnetic interference,high sensitivity and the capacity to identify the defect types.Therefore,it becomes a focus of research in this field.But the fault diagnosis method based on DCA can completely suitable for DC SF₆ gas insulated equipment needs lots of experimental demonstration.In order to provide theoretical basis for improving the fault diagnosis method based on DCA of DC SF₆ gas insulated equipment,this paper will carry out the research on the influence of DC PD decomposition characteristics of SF₆ under metal particle defects,and provide theoretical and experimental support for the establishment and improvement of DC SF₆ gas insulated equipment insulation fault diagnosis technology.In this paper,through a large number of SF₆ high voltage DC PD decomposition experiments,the metal particles is studied on the influence of the geometric dimensions on SF₆ decomposition characteristics.The characteristic quantities for internal PD fault diagnosis of DC SF₆ gas insulation equipment is established and by constructing reasonable and effective characteristic quantities,the fault degree of SF₆positive/negative DC PD can be characterized.The main conclusions are as follow:?1?Five stable products?CF₄,CO₂,SOF₂,SO₂F₂ and SO₂?are selected as the characteristic components of SF₆ decomposition under DC PD.The total formation of sulfur-containing characteristic components C_S,the effective formation rates r_GMS,and the ratio of characteristic components f?SOF₂+SO₂?/f?SO₂F₂?are used to characterize the fault degree of positive/negative DC PD of SF₆.Under the action of DC PD,the generation situation of CF₄ and CO₂ is related to whether the insulation defect model involves organic insulation materials.Therefore,under the condition of metal particle defects,the generation situation of CF₄ and CO₂ cannot characterize the fault degree of DC PD well;The analysis of three kinds of sulfur-containing characteristic components?SO₂F₂,SOF₂ and SO₂?is focused in this paper shows the volume fraction and total formation of SO₂F₂,SOF₂ and SO₂ have a significant correlation with the geometric dimensions of metal particles.The feature shows a growth trend with the time of PD.The fault degree of the wire-type particles will be higher than lamellar particles and spherical particles,and is inversely proportional to the diameter,proportional to the length with the time of PD.?2?Under the action of DC PD,the effective formation rates of the three sulfur-containing components is shown as:SOF₂>SO₂F₂>SO₂;The effective formation rates under the condition of different shapes is shown as:the wire-type particles>lamellar particles>spherical particles;The effective formation rates of the three sulfur-containing components were all ordered by diameter is shown as:0.3mm>0.4mm>0.5mm>0.6mm;By Length is shown as:3mm>5mm>7mm>9mm.?3?The ratio of characteristic components f?SOF₂+SO₂?/f?SO₂F₂?can be used as an important basis for effectively identifying the defect types of metal particles under the action of positive/negative DC PD.Experiments show that with the time of DC PD,the degree of SF₆ insulation degradation caused by metal particles with different geometric dimensions can be identified,and the PD caused by the wire-type particles is the most serious.The research in this paper provides theoretical basis for improving the fault diagnosis method based on DCA of DC SF₆ gas insulated equipment.