| With the increase of the electrical load, there has been an energy shortage of power system as well as the shortage of transmission corridors. The paper concerns the reconstruction of AC network in order to increase its transmission capacity. A New Compact Power Transmission System is proposed in this paper aimed at improving this situation.Firstly, four kinds of topology are proposed with the theoretical analysis of each topology. Under the comprehensive consideration of the applications,construction cost and the control complexity,two topology are finally chose, one is called headline scheme,the other one is called cable scheme. The paper built a mathematical model for each scheme,and estimated the parameter cooperation of the main equipment.Secondly, for the headline scheme,the paper studied the current modulation of the third polar, designed a reasonable strategy to improve the system transmission capacity, and realized this idea based on the interpolar transfer switch. On the other hand,for the cable scheme,concerning the charge accumulation effect of cable,the paper applied the voltage modulattion, and focused on the mechanism of current control. What is more, the capacity expansion of both is calculated and the simulation of both scheme proved the applicability of the strategy.Thirdly, the paper made a perliminary study on overvaltage and insulation co-ordination of the New Compact Transmission System, parted the system into three region, AC zone, Convertion zone and Transmission zone, and simulated the typical fault in PSCAD/EMTDC to visualize the transient overvoltage. Futhermore, the proper installation of MOV arrester could restrain the overtage effectively.In conclusion, the New Compact Transmission System could make full use of the current-carrying capability of three transmission lines, which would lead to the increase in the transmission capacity. Compared to tripolar HVDC, this scheme is easier to implement and performs more economy. |
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