| The arcing of the air gap due to discharge is the main cause of the external insulation damage of the power system,and the post-arc recovery process of the discharge channel determines the recovery performance after the gap breakdown.The flow field in post-arc is a key factor affecting the recovery process,but the current observation is limited to optical and electrical methods,and there is a lack of direct observation results of the flow field,therefore,the post-arc recovery process is not clearly understood.For the two types of freedeveloping arcs that are common in power systems,this paper proposes a flow field observation method,builds a corresponding observation system,and obtains the recovery characteristics and the corresponding flow field evolution characteristics during the postarc recovery process.The relationship between arc channel recovery and flow field evolution is analyzed.Taking the arc equivalent resistance as the characterization quantity and the energy dissipation dominated by the flow field as the dominant factor,a calculation method for the post-arc recovery time is established.Firstly,the post-arc recovery process of a freely developing arc is an evolution process dominated by the flow field.This paper proposes a method using the schlieren technique to observe the flow field of the post-arc channel,and designs a large-field,high-sensitivity,high-temporal-resolution schlieren system with a field of view of 40 cm.A comprehensive experimental platform including flow field,optical and electrical measurement systems have been built for comprehensive observation of the post-arc recovery process with microsecond time resolution and submillimeter spatial resolution.This lays a foundation for the study of the post-arc recovery process.Then,based on the established comprehensive experimental platform,the recovery process of the 30-50 cm spark arc,the recovery process and the rebreakdown characteristics of the 30 cm short-circuit arc were studied.Using the proper orthogonal decomposition method and the optical flow method,the flow field and its structure during the recovery process of the arc channel were analyzed.The evolution of the high-temperature gas in the post-arc channel during the recovery process were obtained.It was found that the hightemperature gas moved in the form of turbulence,the dominant structure of the flow field is a low-frequency large-scale structure,and the movement of high-temperature gas in recovery process has two dominant stages: radial movement and axial movement.The upper limit of the thermal recovery time is determined according to the coefficients of the proper orthogonal decomposition.Based on the voltage and current waveforms,two types of channel resistance and injected energy were calculated.The resistance of the spark arc is in the order of Ω/cm,and the injected energy is 20～160 J.While the resistance value of the short-circuit arc is below the order of Ω,and the injected energy is 2000～6000 J.Through the statistics of optical images,the post-arc luminescence duration of the two types of channels is in the order of ms and hundreds of ms respectively.Finally,the equivalent circuit model of the post-arc element was established.From the perspective of energy balance,the calculation method of the equivalent model parameters was proposed,and the energy dissipation time of two types of arcs was calculated as the lower limit of the thermal recovery time.Finally,for the convenience of application in engineering,two simplified calculation methods for the post-arc recovery time of freedeveloping arcs were proposed,and the actual cases of insulator string flashover and artificial short-circuit in DC line were used as representatives to calculate the recovery times. |
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