| Converter Converter transformer is the key equipment in UHVDC/UHVDC transmission project.The severe operation environment leads to high pressure of safe and stable operation of converter transformer for a long time.The valve side outgoing line device of converter transformer belongs to multi-layer "liquid-solid" insulation structure,which bears the comprehensive effect of AC,DC and AC/DC composite voltage during operation,and is the place where insulation fault occurs frequently.Space charge/interface charge is the key factor that affects the insulation performance of valve side outgoing line device of converter transformer.At present,for the actual measurement and simulation analysis of space/interface charge distribution of large-scale multilayer "liquid-solid" oil paper insulation structure,one is the lack of effective test means,the other is that the existing simulation methods of space/interface charge distribution are not fully applicable.To carry out the simulation and deduction calculation model research on the space/interface charge distribution of multi-layer"liquid-solid" oil paper insulation system,and master the space/interface charge distribution characteristics of multi-layer "liquid-solid" oil paper insulation system under DC,AC and AC/DC composite voltage through the joint means of simulation and measurement,as well as its influence on the electric field distribution,will be for the analysis and elimination of the discharge fault of converter rheologic insulation The optimization design of edge structure provides theoretical basis and support.Based on the bipolar carrier model,this paper studies the simulation method of space/interface charge motion characteristics of multilayer "liquid-solid" oil paper insulation system under DC,AC and AC/DC composite voltage,and verifies the effectiveness of the simulation parameters through the experiment of electroacoustic pulse measurement.Then,the space/interface charge distribution characteristics of"liquid-solid" oil paper insulation system under DC voltage are simulated and analyzed,and the deduction calculation model is studied.On this basis,focusing on the dynamic change of space/interface charge with phase under AC voltage,the space/interface charge distribution characteristics of "liquid-solid" oil paper insulation system under AC and AC/DC composite voltage are simulated Analysis and deduction calculation model research.Finally,aiming at the multi-layer flat structure of typical "liquid-solid" oil paper structure system and the scale-up model structure of converter and rheometer outlet device,the simulation analysis of electric field distribution considering the influence of space/interface charge under DC,AC and AC/DC composite voltage is carried out,and the simulation results of electric field distribution are compared with the measured results of Kerr effect.The main research results and innovations are as follows:? Combined with bipolar carrier model,Maxwell Wagner equation and Poole Frenkel equation,the space/interface charge simulation model of simple multilayer"liquid-solid" oil paper insulator under DC voltage was established.On this basis,the polarity judgment operator was introduced to dynamically change the charge amount and polarity under AC voltage and AC/DC composite voltage.? On the basis of typical simple "liquid-solid" oil paper insulation model,the interface charge density and total charge amount calculation model of multilayer oil paper insulation system under DC voltage based on "field temperature translation factor" and "structure translation factor" were proposed.The increase of field strength and temperature will lead to the exponential increase of the steady-state interface charge density and total charge of the multi-layer "liquid-solid" oil paper insulation system.Through the "field temperature translation factor" proposed in this paper,the interface charge density calculation model under the joint action of field strength and temperature is constructed,and the steady-state of the "liquid-solid" oil paper insulation system under the specific temperature and field strength is realized On this basis,by fusing the"structure translation factor",the calculation model of the total charge of the system under the combined action of the field strength,temperature and structure is further constructed,and the total charge of the "liquid-solid" oil paper insulation system under multi-layer structure with field strength and temperature is realized.? Focusing on the dynamic change of space/interface charge under AC and AC/DC composite voltage,a calculation model of space/interface charge density and total charge amount of multilayer "liquid-solid" oil paper insulation system under AC and AC/DC composite voltage was established.Under AC voltage,the density and polarity of space/interface charge in the system change with the dynamic change of applied field strength and phase.By combining the field temperature translation factor" and the phase influence factor,the calculation model of interface charge density and total charge amount of "liquid-solid" oil paper insulation system under the combined action of specific phase angle,field strength and temperature under AC voltage is established When the ratio of AC voltage to DC voltage is less than 1:1,the influence of DC voltage on space/interface charge is dominant.When the ratio of AC to DC voltage is less than 1:1,the effect of DC voltage on space/interface charge is significant.When the ratio is greater than 1:1,the influence of AC voltage on space/interface charge is prominent.By combining the "field temperature translation factor" and the AC/DC voltage ratio influence factor,the structure of the space/interface charge distribution is constructed The calculation model of interface charge density and total charge quantity of "liquid-solid" oil paper insulation system under AC/DC composite voltage under the combined action of AC/DC voltage ratio,field strength and temperature is proposed.?According to the typical flat multilayer "liquid-solid" oil paper insulation system and the scale structure of converter transformer outlet device,the electric field calculation results considering the space/interface charge influence and the field strength measured by Kerr effect under DC,AC and AC/DC voltage are compared and analyzed,which verifies the effectiveness of the space/interface charge simulation method of "liquid-solid" oil paper insulation system in this paper.By comparing the field strength of each oil duct measured by Bickel effect method and the field strength value obtained by simulation,it is shown that the error between the simulation result and the measured result of flat plate structure under DC voltage is 1%-1.5%,and the error between simulation result and measured result under AC voltage is 4.4%With the increase of the distance from the high voltage terminal,the field strength at the oil duct obtained by simulation decreases,which is consistent with the measured results.The error between the simulation results and the measured results of the electric field distribution of the scaled model structure of the outlet device under DC voltage is:the error of the first oil duct is 7%,the error of the second oil duct is 4.4%,and the error of the third oil duct is 1.3%. |
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