用“场—路”结合方法分析具有直流偏磁的机车变压器空载合闸

Analysis of No-Load Closing of Locomotive Transformer with DC Bias by a Method of Field-Circuit Combination

运行于双流制下的电气机车,直流供电时其变压器用作滤波,此时高压绕组支路并联开路,低压绕组串入直流回路.当机车从直流电网进入交流电网时,由于运行于直流电网时留下了剩磁,合闸到交流电网瞬间将出现较大的冲击电流.采用“场—路”结合的方法分析交流合闸过程,即在磁场分析基础上获得磁化曲线,并做分段线性化处理,据此计算磁路的微分(增量)磁导,进而计算电感,然后列写以磁链为变量的合闸过程的电路方程,再结合磁化曲线求解,得到交流合闸的“电流—时间”关系.结果表明,与单一交流制下运行的变压器相比,由于合闸瞬间铁芯中存在剩磁,这类变压器暂态过程的冲击电流较大,持续时间较长.

For the electric locomotive running under the dual-current system,its transformer is used as filter when the DC power is supplied.At this time,the high-voltage winding branches are open in parallel and the low-voltage winding are connected to the DC circuit.When a locomotive runs from DC supply to AC,a large impact current will appear instantly due to the residual magnetism caused by previous operation powered by DC.In this paper,magnetic field analysis is first done and then the magnetization curve of the corresponding magnetic circuit is calculated,and it is processed in piecewise linearization.Differential(or incremental)magnetic conductivity of the concerned magnetic circuit can be calculated by magnetic circuit Ohm's law and inductance are obtained easily.Then a circuit equation about magnetic chain can be written for the switching process of the transformation at no-load and we can get the magnetic chain curve by solving it.Finally by combining the magnetic chain curve with magnetization curve,the current time curve can be calculated.The analysis shows that the impulse current in the transient process of the transformer is larger and lasts longer compared with the transformer powered only by AC supply,which is due to the existence of large residual magnetism in the core.