| As an important electrical equipment of power transmission and distribution system,high-voltage switchgear undertakes the important task of controlling and protecting power equipment.In the high temperature and high humidity operating environment,the switchgear is easy to form arc breakdown and even ignition accidents.Aiming at the typical flame-retardant insulators in high-voltage switchgear,this paper has carried out a series of ignition experiments under the action of external surface arc and internal breakdown arc,so as to reveal the mechanism of the effect of arc position on the ignition and combustion characteristics of flame-retardant insulators.The research work carried out in this paper mainly consists of the following aspects.Firstly,in order to study the change characteristics of fire ignition parameters of in-service flame-retardant insulators in high-voltage switchgear under high temperature and high humidity,this paper selects the fixed sealing pole that have been in service for 12 years and its new samples with the same formula.And the comprehensive tests of TG-DSC,TG-FTIR,MCC and SEM were carried out.Based on the calculation of pyrolysis kinetic parameters of flame retardant epoxy resin,the influence of ambient temperature in switchgear on the service life of this type of insulation was studied.The results show that the high temperature and high humidity environment in the highvoltage switchgear is easy to cause the structural damage of epoxy resin composites.The main causes are the molecular chain fracture of polymeric materials and the phase separation of inorganic materials.In addition,the high temperature and high humidity operating environment is also easy to make the phosphorous flame retardants in the materials absorb water to form phosphoric acid compounds,which leads to the decline of the insulation performance of insulating materials,and induces the arc breakdown of insulators and the development of subsequent fire accidents.The service life analysis of epoxy resin flame retardant insulator under different ambient temperatures shows that when the temperature is 80℃,the service life of the material is about 12 years,which is consistent with the actual operating conditions and accident occurrence parameters of the high voltage switchgearThen,based on the "high voltage and long distance" arc design concept,a highvoltage breakdown arc simulation and insulating material ignition experimental platform with a maximum power of 60kW is built.The platform can realize the breakdown voltage of 0～25kV and arc length of 0～30mm.which provides conditions for the ignition experiment of flame-retardant insulators with different thickness and layout.n addition,the breakdown voltage is automatically controlled by program.Based on the intelligent control of "arc starting period and intermittent period",the time accuracy control can reach 0.1s,realizing the accurate control of "single type" and"composite type" arcs,which provides important basic conditions for the study of ignition mechanism of flame-retardant insulation under the action of arcs with various time.Focusing on the importance and necessity of arc temperature parameters for the analysis of material ignition characteristics,aiming at the problem that the instantaneous ultra-high temperature arc is difficult to be measured directly,an arc temperature inversion estimation method combining "the measurement of the surface temperature rise curve of the circular ceramic tube heated by internal arc breakdown and the numerical simulation of the external temperature of the ceramic tube under different arc column temperatures" is proposed.The approximate temperature of typical arc in this paper is calculated and analyzed.The results show that the surface temperature of arc column is about 7500K,which provides necessary basic parameters for the mechanism analysis of subsequent arc ignition of epoxy resin insulators.Based on the above experimental platform,the dynamic coupling development process of arc breakdown and material ignition of typical insulators under the action of external surface arc is studied.The results show that although the electrode breaks down along the shortest path on both sides of the flame retardant insulator sample,due to the rapid heating of the arc to the adjacent area,the clamping ignition and combustion process of the inverted "U" arc is quickly formed.Under the heating action of ultrahigh temperature arc,the heating zone of insulating samples presents complex expansion phase transition and intense combustion characteristics,in which the temperature rise rate at typical positions on the surface can reach 180℃/s.After the top of the sample is ignited,the arc then ablates the lower area and continuously forms downward internal breakdown.The moving speed of the breakdown arc can be described in two stages.In the initial stage,the downward movement speed is slow,and the speed of V0 and V1 flame retardant epoxy resin samples are 2.55 and 1.74 mm/s respectively.In the second stage,the downward movement speed of the breakdown point increases to 78.5 and 35.03 mm/s respectively.The insulation samples with higher flame retardant level have better flame retardant ability,but the arc penetration speed is faster.In order to further analyze the influence of the mass fraction of flame retardant on its fire resistance and comprehensive properties,five epoxy resin insulation samples with different mass fractions of flame retardant were prepared based on the formula of V0 and V1 flame retardant insulation.Aiming at the internal crack defects of insulators,the experiments on ignition characteristics under the action of internal small hole(aperture 1mm)breakdown arc were carried out,as well as a series of experimental studies on mechanical and electrical properties.The results show that the ignition and combustion behavior of the insulator under this condition is significantly different from that of the external surface breakdown ignition.Firstly,under the action of ultra-high temperature arc,a large amount of combustible pyrolysis gas is rapidly generated in the small hole,forming a rapid horizontal flame,and the spray rate can reach about 5m/s.Under the action of internal breakdown arc,the mass fraction of flame retardant has little effect on the ignition process and surface temperature evolution characteristics of the samples.However,the samples with high mass fraction of flame retardant showed very strong combustion inhibition during the residual flame action period.In addition,the mechanical properties,electrical properties and ignition and combustion properties under the action of arc of five kinds of insulators are comprehensively analyzed by using the multi-level factor normalization accumulation method.The results show that the samples with relatively high mass fraction of flame retardant has the best comprehensive performance,and the samples with FR-EP-1 has the worst comprehensive performance. |
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