Design And Optimization Of The Constant Voltage Power Transformer Structure For Electrified Railway Power Supply System

There are a large number of different types of non-traction loads along the electrified railway,such as communication,signal,power lighting,etc.The quality of the power supply is directly related to driving safety,operating costs and construction investment.However,for a long time,due to the lack of thorough research and enough attention to the problem of electricity power load,there is a situation of power shortage with the power loads or the problem which cannot be solved economically and reasonably.Therefore,two kinds of 2x27.5/10kV constant voltage power transformers(CVT)are designed.The input voltage is taken from the railway catenary,and the output voltage is used as the power source for non-traction loads,which effectively reduces the railway construction cost and solves the problem of low power reserve.Firstly,on the basis of different types of traction transformers,voltage conversion formulas of 2×27.5/10kV three-phase(D,y11,Y,d11,D,d0,Y,y0)and two-phase(inverse Scott)transformers are derived.And the curve of the output voltage unbalance and the harmonic value injected into the grid are given.The most suitable and optimal connection form for the constant voltage transformer is selected accordingly.Secondly,according to the characteristics of the railway catenary voltage,a constant voltage technology based on the improvement of the coil structure parameters is designed.The main contents are as follows:Firstly,the electrical transformation formula of CVT is derived under the grounded series capacitor and the three-phase taps k1,k2 and k3.Based on this,the different capacitor values are compared with the output voltage amplitude and phase angle,and the influence of the output voltage vs the input voltage is analyzed when C=6?F.The second is to develop the control strategy of the tap and capacitor switch,and customize the D,y11 transformer module with adjustable three-phase turns ratio,the regulation range of this scheme is 23?33kV through simulation.The third is to make prototypes in the transformer factory according to the simulation parameters,and 8 experiments are carried out based on the field equipment.Then,a constant voltage tansformer structure about harmonic restraining transformer based on resonance-circuit and magnetic air-gap shunt is designed.Firstly,the equivalent circuit model is established according to the working principle,and the calculation formula of the air gap length and the nonlinear inductance is derived.According to this,the resonance-constant voltage structure and parameters suitable for railway catenary to take power are designed and calculated.Secondly,since the resonance-constant voltage performance is closely related to the core magnetization curve,this dissertation obtains the B-H curve by measuring the input voltage and current.Then,the polynomial fitting of the magnetization curve is used to obtain the circuit diagram which can truly reflect the dynamic characteristics of the resonance-constant voltage transformer,and the simulation analysis is carried out in Simulink.Finally,based on the core structure and parameters of the resonant-constant power transformer,the Ansoft software was used to simulate and analyze the performance of different working conditions.Finally,since the lower limit of the above two schemes is less than 19kV,the railway catenary power demand cannot be fully satisfied.Therefore,the resonance-constant voltage power transformer is improved and optimized.The output coil is connected to the compensation coil with reverse polarity,and the primary side uses tapped windings.Both theoretical and simulation results show that it has the effect of improving the stability of the input voltage,expanding the voltage regulation range and maximizing the operation in the highest power factor state.Strengths and weaknesses of the three voltage regulation schemes are compared and analyzed,and the applicable places are given.