Small Reactors On Neutral Points Of500kV Autoconnected Transformer Design And Construction Manage

With the constant enlargement of ultrahigh voltage power system and the capacity, thenumbers of500kV transformer substation in Foshan surrounding area are on the increase, ofwhich the average station spacing is less than50km. The transformer substations are largescale and they all use autotransformer with neutral grounding, which may lead to the singlephase short-circuit current greater than the three-phase short-circuit current for most bus.Additionally, the220kV system is also expanding constantly and totally accesses twenty-eight220kV transformer substations in Foshan by the end of2011, which results in the increasingof short circuit current on220kV side. Therefore, to increase the power distribution reliabilityand utilization rate of500kV main transformer, reduce the limitations to the development ofpower grid by short-circuit current level and enhance the flexibility of Foshan power systemoperation mode, small reactance might need to be installed at the500kV autotransformerneutral point to limit220kV bus single-phase short-circuit current.It has been some time for the research and application of500kV autotransformer neutralgrounding by small reactance and the study on its effect and selection calculation arecomparative maturity. Generally, the bus single-phase short-circuit current connected with themain autotransformer that installed with small reactance should lower than the three-phaseshort circuit current. Considering the adaptation of the power grid vision, the small reactanceshould have a certain margin to meet the demand of power grid development in future severalyears. Actually, the original design of the neutral point of500kV transformer substation isbasically achieved by the direct grounding way. And the construction of small reactance isgenerally late technology transformation project, of which the process of design andconstruction should consider the practical situations of different transformer substation.Furthermore, there is not pertinent standard of design and construction for the neutral pointsmall reactance. Thus, the correct design, reasonable construction and analysis for the keystep are very important.Firstly, this study deeply analyses the design and actual construction for the threeprojects of Foshan500kV autotransformer neutral grounding via small reactance. The threeprojects respectively embody the adjustment of the process of neutral grounded by the smallreactance under different construction conditions, which basically contain three installingways: near, medium and far. At the same time, through lateral correlation, we can find out thekey and dangerous points of the design and construction, and make the pointed controlmeasures. Secondly, on the basis of Shunde500kV transformer substation project, corresponding with the construction processes, this study develops the design andconstruction scheme, and then makes track analysis, validates design and construction scheme,as well as the validity of the control measure of the key and dangerous points. Finally,reducing engineering failure and improving engineering quality are realized, and providereference for the later working that with the same type.