单相变压器直流偏磁试验与仿真

Test and Simulation for Single-phase Transformer Under DC Bias

6台单相变压器组成三相组式变压器,分别对变压器开路、低功率三相四线制对称负载、低功率三相四线制不对称负载、低功率三相三线制不对称负载和额定功率下三相四线制对称负载5种情况下的变压器一次绕组电流、一次和二次绕组电压就不同直流入侵情况下进行了测量。研究变压器以上5种工作状态下,直流入侵导致的励磁电流和一次绕组电流畸变和谐波分布、一次绕组电流峰值和各次谐波与直流电流的关系曲线、不同运行方式对直流偏磁的影响。试验发现,变压器直流偏磁将导致空载电流畸变,空载电流峰值及各次谐波随直流电流的增加直线上升。谐波阶次越低,增加速度越快。变压器负载情况下,功率越大,奇次谐波随直流的变化增加速度越慢,偶次谐波增长速度基本不受负载的影响。利用非线性磁滞回线与励磁电流波形的关系,对试验模型进行了仿真计算,同时得到了变压器铁心无直流偏磁和有直流偏磁下的磁滞回线。计算模型建立在Jiles-Atherton理论基础上,计算与试验吻合较好,验证了变压器非线性模型的有效性和正确性。

Experiment on single-phase transformer with DC bias was performed. Six single-phase transformers constitute two three-phase transformers. The waveforms of exciting currents and first winding currents of such three-phase transformer with different DC bias and different loads were measured. Harmonic distribution of exciting currents and first winding currents was gained by FFT. Test results show that exciting current or first winding current will be distorted when DC current flows from neutral point through the winding. The peak value and various harmonics＇ amplitudes of exciting currents or first winding currents increase with DC current linearly. The lower the harmonic order, the more rapidly its amplitude increases. The transformer with three-phase and three-line connection load is much easier to be offset than that with three-phase and four-line connection load when their loads are identical. The bias extents of three phases are different because of different DC current distribution among them. Because the nonlinear characteristics of transformer result in transformer bias, the relation between magnetic hysteresis loop and exciting current waveform was discussed. Based on the Jiles-Atherton theory the exciting current under DC bias was computed. The hysteresises of transformer core with no DC bias and with DC bias were also obtained. The computation result is in accordance with test result and thus the computation model is approved to be correct and effective.