Study on Secondary Side Overvoltage Mechanism of Choke Transformer

A choke transformer is the core equipment of a Track Circuit. It not only ensures the independent operation of adjacent Track Circuits without interfering with each other, but also provides a path for traction current return in adjacent sections. In recent years, with the continuous increase of railway load, overvoltage faults on the secondary side of the choke transformer caused by excessive unbalanced traction current frequently occur, which seriously affects the normal operation order of the railway system, and the industry lacks a mechanism for this fault. Scientific explanations and researches have made no feasible prevention and control methods on the railway. This article takes the BES2 choke transformer as an example. First, the basic structure and working principle of the choke transformer are explained. Then the T-equivalent circuit analysis method of the transformer is used to establish the simulation circuit model of the choke transformer. By simulating the occurrence of overvoltage on the secondary side of the choke transformer, the characteristics of overvoltage fault on the secondary side of the choke transformer are studied. Finally, the paper analyzes the influencing factors of the overvoltage fault on the secondary side of the choke transformer, and discusses the change law of the secondary side voltage of the choke transformer under the influence of unbalanced traction current. This study shows that the unbalanced traction current has the characteristics of a current source. After the choke transformer air switch is disconnected under the influence of the large unbalanced traction current, the secondary circuit impedance surges, which causes the occurrence of overvoltage faults on the secondary side. The relationship between the secondary voltage U
₂
and the unbalanced traction current I
_ub
is given.