Determination method for loss minimum configuration considering reconnection of distributed generators

Global warming caused by carbon dioxide (CO2) and other greenhouse gases is one of the serious environmental issues. Carbon dioxide is the biggest contributor to global warming. Many efforts to reduce emissions of CO2 are carrying out in various fields. In the field of electrical power system, various approaches, such as utilization of renewable energy, loss reduction, and so on, have been taken to reduce CO2 emission. So as to work toward this goal, the total number of distributed generators (DGs) using renewable energy, such as photovoltaic generation system and wind turbine system etc., connected into 6.6 kV distribution system has been increasing rapidly. The DGs can reduce distribution loss by appropriate allocation. However, when a fault occurs such as distribution line fault, bank fault and so on, DGs connecting outage sections are disconnected simultaneously. Since the simultaneous disconnection of DGs influences restoration configuration and normal configuration after the restoration, it is necessary to determine the system configuration in normal state considering simultaneous disconnection of DGs. In this paper, the authors propose a computation method to determine the loss minimum configuration considering reconnection of DGs after simultaneous disconnection by fault occurrence. The feature of determined loss minimum configuration is satisfying with operational constraints even if all DGs are disconnected from the system simultaneously. Numerical simulations are carried out for a real scale distribution system model in order to examine the validity of the proposed algorithm. Figure 1 shows the system model consists of 4 distribution substations, 72 distribution feeders, 252 sectionalizing switches (configuration candidates are 2252) and 120 DGs (total output is 38.46 MW which is 23% of total load). Table 1 shows distribution loss of three cases configurations: case 1) the loss minimum configuration without consideration of DGs, case 2) the loss minimum configuration considering output of DGs and case 3) the loss minimum configuration considering reconnection of DGs. Table 2 shows total amount of overload by simultaneous disconnection of DGs in each configurations. From Tables 1 and 2, when DGs are disconnected from the distribution system simultaneously, it is seen that the overload occurs in case 2 determined by conventional method. On the other hand, case 3 determined by proposed method can be satisfying with all operational constraints even if all DGs are disconnected from the system. As the results of numerical simulation, it can be confirmed that the proposed method determines the loss minimum configuration keeping reliability of power supply in simultaneous disconnection of DGs. Fig. 1. Distribution system model with many DGs