基于磁通实时跟踪的单相四柱式变压器典型工况剩磁特性

Residual Flux Characteristics of Transformer with Single-phase Four-limb Core Under Typical Conditions Based on Real-time Flux Tracking

变压器铁芯在直阻测量、断路器分闸等操作时会产生剩磁,其根本原因是由于铁芯铁磁材料磁滞特性。首先研究了基于带基线修正积分算法的铁芯磁通计算方法,提出了基于磁通实时跟踪的变压器剩磁测量方法。测试结果表明,正弦电压积分的趋势项会使得磁通波形偏离正常值,采用带基线修正积分算法能够有效消除正弦波形积分的趋势项,得到准确的磁通测量结果。然后,参照特高压变压器主体变的铁芯结构型式,等效设计了单相四柱式变压器模型,并在实验室搭建剩磁模拟试验回路,开展了直流电流激励、断路器分闸2种工况的变压器剩磁特性研究。直流激励试验结果表明,变压器铁芯零初始剩磁时直流电流激励与剩磁之间呈现先增大后减小的规律,在磁化膝点处剩磁值最大,约占饱和值的52.63%。当铁芯存在初始剩磁时,由于剩磁的牵制作用,同向直流注入后剩磁几乎不随着直流电流激励的变化而变化。断路器分闸试验结果表明,分闸后铁芯剩磁与分闸角度呈现近似余弦统计分布规律,0°和180°分闸铁芯剩磁最大,约占饱和值的58.2%;90°和270°分闸铁芯剩磁值最小,约占饱和值的4.14%。

Residual flux of core can be generated by DC resistance measurement and circuit breaker opening of transformer,which is mainly derived from the hysteresis characteristic of ferromagnetic material of core.Firstly,the flux computation method based on integral algorithm with baseline correction is studied.The residual flux measurement method based on real-time flux tracking is then proposed.Test results show that the deviation of flux waveform from the normal value will be generated by the trend term due to sinusoidal voltage integration.The integral algorithm with baseline correction can effectively eliminate the trend term,which provides the accurate flux measurement results.Afterwards,a transformer model with single-phase four-limb core is designed according to the core structure of main transformer of UHV transformer,and the simulation test circuits are built in laboratory to investigate the residual flux characteristics of the transformer model after DC excitation and circuit breaker opening.The experimental results of DC excitation show that the residual flux and DC current regularly vary as follows:first increasing and then decreasing when the initial residual flux of core is equal to zero.At the knee point of magnetization curve,the residual flux becomes the largest,accounting for about 52.63%of the saturation value.By contrast,the residual flux has hardly changes with variety of DC current excitation when the non-zero initial residual flux exists in the core,which is mainly caused by the impediment of initial residual flux.The experimental results of circuit breaker opening show that the relationship between residual flux and opening angles presents an approximately statistical cosine distribution.The residual fluxes of 0°and 180°are the largest,accounting for about 58.2%of the saturation value,while the smallest values of 90°and 270°are obtained,only accounting for about 4.14%of the saturation value.