地磁感应电流对变压器匝间绝缘热老化的影响研究OA

Geomagnetically induced current(GIC)introduces quasi-direct current bias into oil-immersed power transformers during geomagnetic disturbances,leading to core saturation,abnormal loss increase,and accelerated thermal aging of inter-turn insulation.The hotspot temperature rise is a key factor governing insulation degradation and lifetime reduction.Quantitative evaluation of the coupled electromagnetic-thermal behavior and insulation aging characteristics under different GIC levels is required for transformers operating under rated load conditions.The objective is to characterize the influence of GIC on loss distribution,hotspot temperature evolution,and thermal aging behavior of transformer insulation systems. A three-dimensional coupled electromagnetic-thermal-fluid model is established for a SFSZ-100000/220 oil-immersed transformer operating under rated load.GIC levels are set as 0 A,30 A,and 50 A.The nonlinear magnetic characteristics of the core are represented using a B-H curve to capture saturation behavior under DC bias.Electromagnetic losses include core hysteresis loss,eddy current loss,winding copper loss,and additional stray losses caused by leakage flux distortion.These losses are mapped as heat sources into the thermal field.A conjugate heat transfer model is used to solve the temperature field,considering solid conduction and natural convection of transformer oil.The inter-turn insulation is modeled as an equivalent thermal thin layer to represent radial thermal resistance.Temperature-dependent oil properties are included to improve flow accuracy.The coupled electromagnetic and thermal fields are iteratively solved to obtain transient temperature distribution and winding hotspot temperature.The hotspot temperature is then introduced into the Arrhenius thermal aging model,and the aging acceleration factor is calculated.Equivalent aging time is obtained through time integration,and insulation life consumption is evaluated based on a reference lifetime of 180,000 h. The results show that GIC significantly increases core magnetic saturation and alters loss distribution.The maximum flux density increases from approximately 1.6 T at 0 A to 2.0 T at 50 A.Correspondingly,core loss and winding loss both increase due to intensified saturation and distorted leakage flux.The hotspot temperature of the medium-voltage winding increases from 361.2 K under normal operation to 378.1 K at 30 A and 390.2 K at 50 A.Under 30 A and 50 A conditions,the hotspot temperature exceeds the standard thermal limit,indicating a reduction of thermal margin and increased insulation stress in upper winding regions.The thermal aging process exhibits strong nonlinear acceleration characteristics.The aging acceleration factor increases from 0.094 at 0 A to 0.602 at 30 A and reaches 2.06 at 50 A,indicating that the aging rate under strong GIC conditions is nearly twice the baseline level.Over a 24-hour operating period,equivalent aging time increases from 2.3 h to 14.4 h and 49.4 h for 0 A,30 A,and 50 A respectively.Long-term evaluation shows that annual insulation life loss increases from 0.457%to 1.067%,which is 1.33 times higher than the no-GIC condition. GIC induces core saturation and loss redistribution in oil-immersed transformers,resulting in increased hotspot temperature and accelerated thermal aging of inter-turn insulation.The coupling between electromagnetic distortion and thermal accumulation leads to significant reduction of insulation lifetime margin.The proposed electromagnetic-thermal-aging framework enables quantitative evaluation of hotspot temperature rise and insulation life consumption under different GIC conditions,providing a basis for insulation aging assessment and operational evaluation of transformers under geomagnetic disturbance environments.