Research on Residual Flux Density Measurement for Single-Phase Transformer Core Based on Energy Changes

When a power transformer is reconnected to the grid, if there is a large residual flux in the iron core, significant inrush current may occur and result in reclosing failure. Thus, accurate measurement of residual flux is necessary to avoid the generating of inrush current. This paper proposes a residual flux density measurement method for single-phase transformer core based on energy changes. After the transformer is de-energized, the core is connected to the external dc measurement circuit. First, when positive and negative DC voltages (referred as the direction along or opposite to the initial residual flux density) are applied, the positive energy of power source islarge than the negative energy and thus the direction of residual flux density can be determined. Then, the residual flux density value is calculated by the empirical formula between positive energy and residual flux density. This paper takes the square iron core as the research object, establishes the corresponding empirical formula by finite element method, and verifies the accuracy of proposed formula on the experimental platform. The experimental results show that the proposed method has higher accuracy.

当电力变压器重新接入电网时，若铁芯中存在较大的剩余磁通量，则可能导致显著的涌流电流，进而引发重合闸失败。因此，对剩余磁通量的精确测量至关重要，以避免涌流电流的产生。本文提出了一种基于能量变化的单相变压器铁芯剩余磁通密度测量方法。在变压器断电后，其铁芯被连接至外部直流测量电路。首先，当施加正负直流电压（指沿或逆初始剩余磁通密度方向）时，电源的正能量大于负能量，从而确定剩余磁通密度的方向。随后，通过正能量与剩余磁通密度之间的经验公式计算剩余磁通密度值。本研究以方形铁芯为研究对象，通过有限元方法建立了相应的经验公式，并在实验平台上验证了所提公式的准确性。实验结果表明，所提方法具有较高的精度。