Study On Electric-Magnetic-Thermal Characteristics Of Anode Saturable Reactor For Converter Valve

High voltage direct current transmission is in a period of vigorous development.As the key switching component of the converter valve in the transmission system,thyristors are prone to damage due to rapid changes in pulse current.Anode Saturable Reactor(ASR)connected in series with thyristors,with their electromagnetic characteristics,spontaneously provide large inductance at the moment of the converter valve turn on,controlling the current change rate within an appropriate level to effectively protect thyristors.Under complex operating conditions,ASR will intermittently generate significant core losses,making it difficult to effectively dissipate the heat generated by the losses under low thermal conductivity insulators.Improper material design or long-term accumulation of heat can lead to uneven body heating,accelerate material thermal aging,and reduce device lifespan.The electrical,loss,and heating characteristics of ASR are closely related.Currently,most teams have conducted isolated and single research on these three characteristics,with insufficient consideration of factors and limited model accuracy.They are also limited by computational complexity and simulation difficulty.The vast majority of teams only study the characteristics of a single iron core and abandon conducting 3D simulation analysis of the entire ASR,ignoring the impact of its structural asymmetry on various characteristics.Therefore,comprehensive consideration of the electrical-magnetic-thermal characteristics of the entire ASR is of great significance for device state evaluation and optimization design.This thesis is based on the study of key electrical performance of ASR,using the quantitative calculation of losses under actual excitation as a bridge,and studying its heating characteristics through the multi-physical field coupling finite element method.Firstly,the equivalent inductance model considering the effect of air gap and the equivalent resistance model based on wave penetration theory are combined to establish the complete equivalent circuit mathematical model of ASR.Simulating the ASR body model under impulse discharge testing on the finite element simulation platform and the Simulink circuit simulation platform,respectively,revealing the electromagnetic characteristics of the ASR body and its response under actual excitation,and verifying the correctness of the equivalent-circuit model.Further analyze the current stress of the converter valve containing ASR during opening and the voltage stress during closing,and verify the effectiveness of the established model in the system.Secondly,by clarifying the mechanism of iron core loss generation and considering the pulse excitation obtained from electrical characteristic analysis,and fully considering the discontinuous and uneven characteristics of core loss,three instantaneous iron loss calculation models,namely hysteresis effect and eddy current resistance iron loss calculation model,IGSE core loss calculation model,and EEL core loss calculation model,were established to solve the problem of difficulty in accurately calculating ASR core loss under non-sinusoidal excitation,and the difficulty of effectively obtaining instantaneous losses.Apply three calculation models to the actual ASR iron core for simulation calculation,and build an experimental platform for experimental comparison and verification.Finally,based on the established model,the core loss of ASR under actual excitation is calculated,and the results are used as a heat source.An equivalent water-cooled model that can greatly reduce the computational workload is used to conduct a three-dimensional electricalmagnetic-thermal multi-physics coupling transient simulation analysis of the entire ASR,revealing the spatial distribution and influencing factors of its temperature.The structural optimization scheme of iron cores combination with different cross-sectional areas is proposed.Under the premise of unchanged electrical performance,the maximum temperature difference between iron cores is reduced to 8.3% of the original temperature difference,and the maximum temperature of epoxy resin is reduced by 3 ℃.Further analysis of the impact of insulation materials with different heat transfer coefficient on the overall temperature of the reactor provides reference for ASR performance verification and parameter design.