Analysis And Criterions Of Loop Closing And Breaking Operation For Distribution Grids

It is necessary to analyse the criterions of loop closing and breaking operation indistribution grids because the overcurrent maked by loop closing operation may affect currentprotection and loop breaking operation can lead to feeder overload.The criterions of currentstudy either by experiment or experience lacks quantitative analysis or theoreticalderivation.The judgment method of load flow calculation or simulation lacks the analysis ofcharacteristics of distribution grids.This paper comes to the criterions of closing or breakingof the loop in distribution grids through the reasonable theoretical derivation and thecharacteristics of the distribution network.Firstly, this paper classifies the calculation methods of the loop current of distribution grids,and analyses the advantages and disadvantages of each method. Secondly, this paperestablishes the reasonable model of the closed loop of distribution network. It obtains thecalculation method of the steady loop current and analyses the transient process of decay. Inaddition, this paper changes the steady loop current RMS algorithm from the vectorcalculation to the scalar calculation. It makes benefits to the analysis of the closed loop ofdistribution grids.In the analysis of judgment conditions of loop closing operation，this paper simplifiesjudgment of the closed loop conditions through the comparison of the loop closing transientshock attenuation time and the current protection II delay time. On this basis, it analysesdifferent distribution network and makes it to be three cases of being able to do the loopclosing operation、not being able to do the loop closing operation and the calculation isrequired to determine whether to do the operation. This paper gives analysis both on10kV busvoltage differences and interconnection switch voltage differences when the calculation isrequired.Finally，this paper makes a strategy of loop closing and breaking operation in distributiongrids. This strategy reduces unnecessary calculation，and some examples are given to show the feasibility of the methodology.