In this paper

a kind of new optimization grouping method on substation capacitor based on reactive power compensation constraints is proposed. Firstly

the up and down limit of reactive power compensation capacity to be allowed to switch by the substation is solved in accordance with the daily load curve and the busbar voltage operation constraint of substation and also by way of flow calculation

and the reactive power compensation constraint is expressed by a interval number. Furthermore

the optimization grouping issue of the capacitor is transferred into the mathematical issue of optimization grouping of the obtained above reactive power compensation interval number

thus a kind of optimization grouping model with minimum number of capacitor installed and minimum operation numbers as objective function and a modified SA（simulated annealing）algorithm is employed to solve this problem. Finally

the calculation example of conventional load curve and combined typical curve on the simplified grid model at certain area is given. It is shown

compared to the other two methods

that the method proposed in this paper possesses effectiveness and reasonability.