Simulation Of Temperature Field In Saturable Reactor And Study On The Characteristics Of Electro-thermal Aging

The main function of the saturable reactor is to protect the normal opening of the thyristor,and its failure will directly threaten the safe operation of the converter valve.The insulation of the saturable reactor endures periodic pulse electro-thermal stress for a long time because of the periodic process of turn on and turn off in the converter valve,which makes the insulation performance of epoxy resin weak area declining rapidly.It is not clear that the aging mechanism of the epoxy resin of saturable reactor in this electro-thermal environment.In order to reveal the aging mechanism of saturable reactor under periodic pulse electro-thermal stress,and quantitatively evaluate its aging life.In this paper,the electro-thermal parameters of the weak point in the internal insulation of the epoxy resin are obtained by the finite element simulation,taking the saturable reactor of the 1100 kV UHVDC rectifier converter valve as the research object.Based on these parameters,an electro-thermal aging test platform for 50 Hz pulse voltage and 50 Hz sinusoidal voltage with equal amplitude is built,and comparing the aging difference.Depending on the Cole-Cole dielectric relaxation model,the aging characteristic parameters are extracted,which provides guidance for revealing the aging mechanism and the aging life evaluation of the local weak in the epoxy resin.Firstly,based on the finite element analysis method,the core loss of the saturable reactor is modeled by ANSYS Maxwell software,transferring transient current data in full load condition of 5000 A,and the transient power of core loss is simulated.Besides,the power density distribution of the core loss is also revealed.At the same time,in order to get the distribution of local maximum electric field of epoxy in saturable reactor,the peak time electric field of saturable reactor under normal working condition is simulated.Secondly,in order to find the position of the hottest spot in the epoxy resin of the saturable reactor,the electromagnetic thermal coupling model of the core is established based on the power density of the core loss of the saturable reactor with the ANSYS Maxwell software,and obtaining the temperature distribution of the core.Furthermore,in order to obtain the temperature distribution of the epoxy resin in the saturable reactor,a multi physical field coupling simulation model of electromagnetic heat flow is built with ANSYS Fluent software.Finally,the hottest temperature value and location inside the epoxy resin are determined.Finally,the combined aging under electrical and thermal stress test of the epoxy resin in the saturable reactor is carried out.In order to study the difference in aging of epoxy resin in two conditions,an electro-thermal aging platform is built with 50 Hz sinusoidal voltage and 50 Hz pulse voltage.According to the simulation results of the highest local temperature in the epoxy resin,the aging temperature is set,comparing the variation of the dielectric properties of the epoxy resin in the two conditions and analyzing the aging mechanism and the difference of the life.In order to quantitatively study the aging characteristics of the saturable reactor under the actual pulsed electric field,the dielectric spectroscopy obtained from electric pulse electro-thermal aging is fitted by dielectric spectroscopy with the double relaxation Cole-Cole model.The relationship between characteristic parameters and aging time of epoxy resin under different aging conditions is obtained,which provides guidance for revealing the aging mechanism and life evaluation of epoxy resin in the saturable reactor.