Evaluation Of Load Supply Capability Based On Security Analysis In Distribution Power System

On the one hand, urban power system is the link of the users and the generation andtransmition power system. And on the other hand, it is an important part of the city planning.For the past few years, the urban power system is developing fast but the problems areexplored such as unreasonable network structure, low reliability and low equipmentutilization, etc. As a result, the traditional power system planning methods needs to develop aswell to satisfy the requirement of lower cost, higher efficiency and intensive development.Load supply capability is a concept to describe the amount of load that can be supplysafely in some urban power system when N-1contingency is occurred. It is significant toarrange the reasonable spare capacity, operate the system, and set the load transfer strategy. Itis based on the pricise calculation to use the concept of load supply capability in the urbanpower system planning. As a result, the comprehensive research of load supply capability iscarried out in this paper. Load supply capability is calculated and analyzed in the MediumVoltage (MV) distributiton power system, High Voltage (HV) distributiton power system, MVdistributon power system with distributed generators. The main research contents are shownas follows:(1) Based on the traditional optimazaiton algorithm and the matrix algorithm of loadsupply capability in MV distribution power system, the modification is put forward in thispaper. Firstly, the indirect load transfer strategy in N-1contingency is added to theoptimaztion model. Sencondly, the indirect load transfer strategy and connection feedercapacity are added to the matrix algorithm, and an iterative modification is introduced tomake the matix algorithm more accurate. Then, the correctness of two modified algorithm isproved though a case study. At the same time, the characteristic of the power supply capabilityis analyzed. Through the comparison of two algorithm, it can also be concluded theperformance and usage range of them. These will be useful tool of power system planning.(2) Based on load capability in MV distribution power system, the concept is extended todescribe the distribution power system including110kV lines and network in the lower votagegrade. Firstly, the matrix model of110/35kV network structure is put forward. In the model,supply route matix is used to describe the network of each kind of connection mode, and theoperating/transferring vecter is used to describe the operation status. Secondly, the powersupply capability model which considering N-1contingency of HV distribution line is built. Then the algorithm is put forward. According to the model, continuous variables and discretevariables are separated and the algorithm combines the simplex algorithm and geneticalgorithm. At last, the correctness of the algorithm is proved through a case study.(3) Taking the load supply capability algorithm considering110/35kV lines’ N-1contingency as a tool, the new planning method is put forward in the HV distribution powersystem. Firstly, through the load supply capability calculation and comparison under differentconncetion modes, the characteristic and usage range of three basic type of connection modesare concluded. They can be good guides of HV distribution power system planning.Sencondly, based on the load supply capability model, a line capacity optimization model isput forward. It aims at the least amount of HV line capacity and the most of load supplycapability. A simplification is introduced to the algorithm to make it more efficiency. At last,the correctness of the algorithm is proved by a case study. The result will be reference in theHV line selection.(4) Distributed generation is introduced to the load supply capability model in the MVdistribution power system. Firstly, the output curves of wind turbine, solar photovoltaic, andlead-acid battery are analyzed as the base of load supply capability research. Sencondly, themodel of distributed generation route is built to describe the impact on load supply capability.And it is introduced to the load supply capability model. Then, the point estimate method iscombined with simplex algorithm to calculate load supply capability according to theintermittency of distributed generation. At last, the correctness of the algorithm is proved by acase study. And distributed generation’s impact on load supply capability is concluded thoughthe data analysis.