A Theory of Maximum Capacity of Distributed Generators Connected to a Distribution System Using Electric Power Density Model

Abstract

Recently, numbers of distributed generators (DGs) connected to distribution systems have been increasing. The system operators should know how large capacity of DGs can be connected without problems to one feeder of the system to control the system appropriately. Conventionally, many studies have presented about the maximum capacity of the DG, but they have been limited results calculated by typical or average value model. However, many DGs will access to one feeder if deregulation of electric power industry is accelerated in the near future. In order to cope with this background, the authors have drawn general formula to calculate the range of the permissible capacity of DGs per one feeder.
In order to deal with sets of DGs that are dispersed on distribution line completely, the authors have drawn differential equation of complex power and one of voltage drop which are expressed by function of distance from a substation by transforming. The general formula to calculate the range of the permissible capacity of DGs connected to the feeder is led by solving these equations under the line voltage, the line current, and the power factor of DGs restriction condition.
As a numerical analysis, the authors have calculated the maximum capacity of DGs depending on many parameters such as the length of the feeder and DGs power factor etc. In a short length of a feeder, the maximum capacity of DGs is ruled by the current restriction condition, but in a long length of a feeder, it is ruled by the upper voltage restriction condition.