基于等效短路试验的变压器用层压垫块累积效应

Cumulated Effect of Spacers in Transformers Based on Equivalent Short-circuit Test

层压垫块是油浸式变压器线圈轴向支撑结构的关键材料之一,多次短路条件下变压器层压垫块的累积效应规律尚不清晰。该文提出适用层压垫块的多次短路等效试验方法,可模拟暂态分量为50 Hz的动态短路力,突破材料尺度上静态试验的局限;试验获得层压垫块在不同短路力大小、老化程度、短路类型和短路次数等条件下塑性形变的变化规律。结果表明:塑性形变与短路力大小有正相关关系并随着短路次数增加呈饱和特性;塑性形变与间隔类型的相互关系并不明显;根据老化15年层压垫块塑性形变规律,将累积效应划分为形变上升、稳定和快速累积3个阶段,老化和力联合作用下层压垫块纤维状态是发生不同累积特点的直接原因;层压垫块弹性模量与短路力呈非线性相互关系。进一步提出变压器轴向预紧力损失计算方法,实例计算表明,多次短路后各线圈轴向预紧力发生下降或再分配现象。研究结论为深入掌握多次短路累积效应对变压器的影响提供一定的技术支撑。

Spacers are one of key materials in the axial supporting structure of coils in oil-immersed transformers.The pattern of cumulative effects on transformer spacers under multiple short-circuit conditions is not yet clear.The proposed method is an equivalent test for spacers under multiple short circuits,capable of simulating dynamic short-circuit forces with a transient component of 50 Hz.This method overcomes the limitations of static load tests in the field of transformer insulation materials.The test results provide insights into the variation in plastic deformation of spacers under different conditions such as short-circuit force magnitude,aging degree,type of short-circuit method,and times of short-circuits impact.The results indicate that plastic deformation is positively correlated with the magnitude of the short-circuit force and exhibits saturation characteristics as the times of short circuits impact increases.The interrelation between plastic deformation and interval types of short circuits is not significant.Based on the plastic deformation pattern of spacers aged for 15 years,the cumulative effects are categorized into three stages:rise,stability,and rapid accumulation.Under the combined influence of aging and load,the fiber state of the spacers corresponds to different stages of cumulative effects.The elastic modulus of the spacers shows a nonlinear relationship with the short-circuit force.Furthermore,a method for calculating the loss of axial pre-tension force in transformers is proposed.Case calculations demonstrate that the axial pre-tension force of each coil decreases or redistributes after multiple short circuits.The conclusions of this study provide technical support for a deeper understanding of the impact of multiple short-circuit cumulative effects on transformers.