Research On Three-stage Optimization Methods Of Switch Placement On A Medium Voltage Overhead Line

In power systems,distribution networks are directly connected with the customers and have a great influence on customers' power supply quality.A reasonable level of distribution network reliability can not only provide a safe,stable and continuous power supply to customers,but also affect the economic benefits of power supply companies and the entire society.The addition of sectionalizing switches on a feeder can optimize the topology of a distribution network,reduce the corresponding fault range,and significantly increase the network's power supply reliability.The problem of sectionalizing switch optimization placement is to determine the reasonable types,number,and installation positions of sectionalizing switches,which belongs to a nonlinear,non-differentiable and combinatorial optimization one.In the current distribution network planning and construction,a reasonable reliability level and the corresponding economical efficiency are closely linked.It has attracted more and more attention to optimize the placement of sectionalizing switches in a medium voltage distribution network in orde to coordinate reliability and economy.A new heuristic algorithm is presented in this paper for the optimal placement of the same type sectionalizing switches on a medium voltage overhead line.In the presented model,a multi-objective function is constructed,which involves two normalized power supply reliability indexes,i.e.,SAIDI(system average interruption duration index)and EENS(expected energy not supplied).The corresponding constraints include the minimum improvement effect of power supply reliability indexes and maximum allowable switch cost.A general criterion of maximum switch position sensitivity is presented to locate a single switch,and thus a three-stage optimization algorithm is proposed for the sectionalizing switch placement of a medium voltage overhead line.In the first stage,based on the line tie connection,reasonable candidate switch placement positions are quickly and intuitively determined;in the second stage,initial placement positions of newly added sectionalizing switches are found one by one;in the third stage,an iterative method is used to adjust the placement positions of the sectionalizing switches.The switch optimization scheme proposed in the case studies not only further improves the reliability level of feeders,but also verifies the rationality of the proposed three-stage optimization algorithm.For the optimal placement of different type sectionalizing switches(breakers and load switches)on a medium voltage overhead line,the objective is to minimize the total cost,which includes the costs of switch investment,switch operation and maintenance,and power outage losses.The formulae for calculating the change of two reliability indexes(SAIDI and EENS)are deduced,which are related with the tie connection situation,switch types(a circuit breaker or load switch)and outage types(power failure or scheduled outage).The algorithm steps are roughly the same as those of the algorithm of the same type switch optimization placement.The difference is that the type and position of a sectionalizing switch are determined by identifying the minimum total costs.The case study shows that the proposed algorithm is reasonable and effective.