| Electric traction has become an important traction power of railway with its unique advantages.According to the Medium and Long-term Development Plan of Chinese railway,electrified railways has been regarded as the main task of railway construction in the future.Railway electrification system is a three-phase unbalance system and the unbalance of the 220 kV transmission network caused by two-phase power supply system is notably serious.With the wide application of two-phase power supply system,the influence of two-phase transmission line on the power system also matters.Nowadays,the 220 kV electric traction power supply line,only uses the power-side protection which can only collects the single electric quantity of the line.The protection devices adopt over-current protection and phase-to-phase distance protection.For this mode of protection,because of the lack of explicit interval selectivity,only power-side protection operates when line fault happens.Otherwise,operation time is too long for protection device to act correctly due to transition resistance and it is hard to satisfy the needs of speed and selectivity of protection devices.On the other hand,the setting calculation and coordination of the protection device can be complicated.Firstly,this paper analyzes three-phase transmission line and two-phase electric traction power supply line in physical structure.Electrical quantities in two-phase transmission lines are derivable from formulas and the results are verified by intelligent operation of power grid simulation training system.Secondly,considering the requirements and the coordination principles of the two-phase transmission lines relay protection at present,this paper summarizes the influence of two-phase transmission line on normal protection devices.The problem of three-phase transmission line protection operating on two-phase transmission line are analyzed from starting component and protective function.Considering the advantages of optical line current differential protection and application of differential protection,this paper studies a completed and integrative protection for two-phase transmission line to improve the stability of power system and the reliability of two-phase electric traction power supply line. |
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