Research On Switching Overvoltage And Its Suppression Technique For High Voltage System Of The Electrical Multiple Units Train

As the electric multiple units trains lifting/dropping the pantograph or opening/closing the main breaker, the electromagnetic transients in the high voltage circuit may produce overvoltage and disturb the onboard electronic equipment, as well as emit high frequency electromagnetic interference, which hazard the normal operation of EMUs.Taking the CRH2EMU as an example, the mechanism of electromagnetic transient during lifting/dropping the pantograph or opening/closing the main breaker is theoretically discussed in detail, and how the relevant parameters impact on the transient is also analyzed. During the process of lifting pantograph, the oscillation frequency is mainly affected by the equivalent inductance, and the transient duration and peak voltage are influenced by both the equivalent inductance and resistance on keeping the cable configuration unchanged. The initial angle has an effect on the magnetizing inrush current of traction transformer and its windings overvoltage as closing the breaker. Besides, the magnetizing inrush current is also influenced by the remanence of the transformer.Then the modeling method of EMUs high voltage system is described. It is necessary to take the skin effect into account in order to calculate the accurate contact wire impedance in the high frequency circumstance. A lifting pantograph model considering the process of the air broken down and the variation of the arc length is presented. The exponential function is used to simulate the V-I characteristic of the arrester, and the voltage transformer can be modeled through UMEC method. Two experiments including the arrester leakage current test and excitation characteristic of voltage transformer test are conducted so that some electrical parameters can be obtained that used in modeling. Also, the traction transformer model that considers excitation characteristic is given.A simulation circuit of the CRH2EMU high voltage system is established with PSCAD/EMTDC, and the paper put emphasis on the electromagnetic transient of lifting pantograph and closing the breaker. The simulation results indicate that the transient voltage is60-75kV, the oscillation frequency is40-70kHz and the transient duration is0.2～1.5ms. The traction windings overvoltage is larger at90°closing angle than at0°while the magnetizing inrush current has the very opposite rule with the closing angle. And the more remanence, the larger magnetizing inrush current. Some measurements of the electromagnetic transients when the CRH2EMU lifts/drops the pantograph and opens/closes the breaker were conducted in the depot. The contact wire voltage, traction windings voltage and cable current were found. The contact wire overvoltage during lifting and dropping the pantograph is about60-70kV. The traction windings overvoltage is about2.9-6.2kV at closing the breaker and2-5kV at opening the breaker. And the magnetizing inrush current is about0.1～0.3kA. The test results can be used to verify the validation of the simulation model.Two methods are put forward and conformed by simulation to improve the electromagnetic transients:inserting inductors or adding RC filters. Their component parameters are all designed, and the RC filter has been manufactured.