Research On20kV Power Supply System Of Intercity Rail

With the rapid development of domestic economy, the density of power load isincreasing continuously. Then the drawbacks of the10kV distribution grid is increasinglyobvious. In order to ensure the power quality, lower the power loss and improve the economyof power system, many regions of China have carried out trials and studies of the distributiongrid system which used the20kV voltage to supply the power. After comparing the pros andcons of the distribution grid system’s proposal to supply the power between the10kV and20kV, this paper makes a deep research on the following problems, namely the mode ofneutral grounding, the setting of the protective relaying and the reactive power compensationin the process of CZT intercity rail10kV distribution grid’s boosting into the20kV. The maincontents of this paper are as follows:1. The superiority of supplying the power with20kV voltage by distribution grid systemis analyzed theoretically, then the three neutral grounding modes of the medium distributiongrid system, namely insulated neutral grounding, neutral grounding by impedance and neutralgrounding by low-resistance are elaborated, also the appropriate choices of neutral groundingmodes of three different transmission lines types (namely the pure cable lines, the pureoverhead lines and mixed lines consisting of cable and overhead lines) are discussed. Aftercombining with the actual situation of CZT intercity railway power system for analysis andcalculation, the mode of neutral grounding by low-resistance is proved applicable for thissystem.2. According to the relevant principles of phase over-current protection andzero-sequence over-current protection for the20kV distribution grid system, analyze thefeasibility of phase over-current protection instead of zero-sequence over-current protection.In connection with the actual situation of CZT intercity rail power system, analyze itstwo-phase short circuit fault and single-phase earthed fault, then deploy the correspondingphase instantaneous over-current protection, over-current protection, zero-sequenceinstantaneous over-current protection and zero-sequence over-current protection for it, andobtain the feasible proposal of phase over-current protection instead of zero-sequenceinstantaneous over-current protection.3. Introduce the theory of determining the amount of reactive power compensation fromimproving the power factor and ensuring the power quality. Under the actual situation of theCZT intercity rail power system, establish the corresponding model by MATLAB, and fromthe voltage loss and power loss simulation of different stations, obtain the appropriate patternof reactive power compensation and the length of the transmission line when its terminal voltage of different stations have just dropped to the provisional value of the qualified voltagewithout reactive power compensation.