The Research On Optimization Method Of Reduced Generating Unit Voltage Operation Schemes

With the fast development of Ultra High Voltage Power Grid,space truss structure is gradually enhanced and the magnitude of short-circuit current increases continuously.On the other hand,with the advancement of national energy conservation and emission reduction work,discouraging small energy-inefficient power plant,generation units with a capacity less than 200MW are gradually shutting down and large capacity units gradually substitute small capacity generator units.If the large capacity of generator units continue to be connected to 500kV power grid,the transformer capacity between 220kV grid and 500kV grid will gradually be enlarged.Meanwhile,it also goes against the operation of power system efficiency.Thus,it will cause a certain reduction of power sources in the 220 kV grids.In the meanwhile,this leads to a large power transmission between 500 kV network and 220 kV network.The feasible ways to alleviate this situation is to reconfigure the generator with high voltage level to the low voltage level network.Therefore,it is important to study the optimization method of unit operation with high voltage level to the low voltage level network.In order to achieve this goal,taking the operation of the generator sets in Hunan province as an engineering background,the following works are carried out in this paper:Firstly,this paper introduces the development status of Hunan power grid and the analysis methods of power system stability.A multi-stage optimization strategy for the operation of generating units with high voltage level to the low voltage level network is proposed.The initial sets of generator reconfiguration schemes are obtained according to the voltage grade of generators,the degree of transmission congestion,the length of first built lines,the ratio between the capacity of a generator connected to a lower voltage level and subarea loads.Secondly,according to the principles of the index,in order to meet the requirements of safety and economy,economic indicators based on the system losses and the capital of the first built lines,voltage deviation rate line over-load rate,static voltage margin,static sensitivity and short circuit current are constructed.Because different indexes have different effect on the evaluation work,so according to the different degree of important indicators should be given different weights to highlight the evaluation index,the index weight is reasonable for the comprehensive evaluation result playing an important role.In this paper,the coefficient of variation is used to determine the weight of the index.Finally,according to the Hunan power grid project,apply the proposed optimization evaluation model and the ideal ranking method based on variation coefficient method to rank the primary schemes,and the results of the two methods were compared and analyzed,which prove the feasibility of two methods.At the same time,calculate the stability calculation and short-circuit current calculation of unit step-down operation plans,the final optimized step-down operation scheme is determined based on a comprehensive analysis and comparison in safety and stability of power grid,and furtherly verify the feasibility of proposed method on unit operation with high voltage level to the low voltage level network.