Research On DC Magnetic Bias And Suppressing Method Of Traction Transformer During Disconnection Of Pantograph-catenary System

Along with the increasing speed, track irregalurity, catenary vibration and pantograph vibration become serious, which will cause pantograph slide away from contact wires and generate arc and spark. Variations of electric contact properties and current collection properties of pantograph-catenary system will produce adverse effects on the traction drive system. The safe operation of the train will be restricted by the current collection quality. Traction transformer is one of the most important links of energy transmission of the traction drive system. So the study of output characterists of traction transformer caused by disconnection is important to study its effects on the whole traction drive system.This paper has studied the arc model which considers the heat transferring coefficient and arc column length, and analyzed the contact pressure between pantograph and contact wires in different speed based on pantograph-catenary coupled model. Traction transformer and four-quadrant converter have been built up in MATLAB/SIMULINK. The arc model and disconnection events are the input of traction transformer, respectively. DC magnetic bias of traction transformer caused by arc and disconnection has been analyzed, so as the FFT characteristics of output voltage and output current caused by DC magnetic bias. Moreover, to study the influence of DC magnetic bias on the traction transformer electromagnetic characteristic, this paper has set up the coupling model of traction transformer and four-quadrant converter. And variations of flux density and inductance caused by DC magnetic bias have been researched. Because DC magnetic bias will make primary current increase and secondary leakage inductance decrease, which will produce adverse effects on winding insulation and increasing THD of secondary current, respectively, and traction motor output torque will be adversely affected by the increasing harmonic. Consequently, this paper has discussed two methods of DC magnetic bias inhibition:one is adding additional winding for flowing into compensation current; the other is improving controlling method of four-quadrant converter to suppress DC magnetic bias. And the second method has been verified on a small power platform in the laboratory.