Study On No-load Closing Overvoltage Of Transformer In Traction Substation Of Ha-da Electric Railway

Different kinds of overvoltages have great difference on characters of duration time, frequency, waveform, amplitude and so on, their harms can't be avoided by using a single protector like arrester. Therefore, it's of great importance to investigate the mechanism of different kinds of overvoltage and to find efficient measures to suppress them. Ha-da electrical railway is the first traction power supply technology imported from Germany, which is different from other domestic power supply system for electrical railway, it uses 220 kV two-phase power supply system, this is the first application in China. On the other hand, the rated voltage of the transformer in traction substation is selected low. These special performances lead to high overvoltage and excitation inrush current generated due to no-load closing of the traction transformer, and cause impact and influence on power system.This thesis carries out simulation study on the commissioning of three traction transformers in Jilin Province. During the commissioning two different kinds of overvoltages were produced successively, which appeared on the two feeding phases and on the third phase respectively. Analysis shows that the first kind of overvoltage is caused by electromagnetic oscillation in system, and the second is caused by the magnetic flux of the power transformer, which is excited by inrush current due to different magnetizing characteristics of the magnetic core of each phase. After studying the computing methods of ATP-EMTP, we construct an accurate stimulating model used in ATP-EMTP for the first kind of overvoltage, and a checking model for the second kind of overvoltage basing on the above judgement. Results of the investigation show that the amplitude of the first kind of overvoltage, which may exceed 2.0 p.u. under some conditions and should draw operators' attention, is related to the entrance capacitance, the parameters of the transmission lines, switching phase-angle, the impedance of the power system and so on. But it can not exceed 2.0 p.u. in the case of our subject, which will not impact the electric power system according to national electric standards. The amplitude of the second kind, which can not be described in detail, is related to the magnetizing characteristics of the power transformer and the amplitude of the inrush current, but we can eliminate this overvoltage by adopting multiloop power supply. In general, the article basically resolves the problem of the overvoltage produced by the commissioning of three traction transformers in Jilin Province. And the factors analyzed in the thesis, which influence the amplitude of the overvoltage, are valuable for the research of the same kind of problems.