Embedded generation impacts to medium voltage distribution network and mitigation techniques

Abstract

As a result of increasing of electricity demand, the electrical transmission and distribution systems are continuously expanding. Connection of Distribution Generators (DG) to the distribution network and upgrading of the transmission lines are more frequent expansions. Connection of new mini hydro power plants (MHPs) in Sri Lanka is one good example. In most of the cases these DGs, which are mainly based renewable energy are located in remote areas. The main bottleneck barrier of connecting DG is violation of fault current ratings at some parts of the network. Some expansions may result in higher fault current level at some points of the power system and thus exceeding the short circuit ratings of equipment such as switchgears and expulsion switches. As upgrading of equipment is not feasible both economically and technically, introduction of fault current limiting devices has become an essential requirement. Fault Current Limiter (FCL) is series device connected to the power system, which shows the high impedance to the current during a fault while showing a zero or low impedance during normal loading condition. Although several FCL topologies were introduced by researchers, there are some technical and economical problems to be solved before introducing them to the power system effectively. It demands the investigation of new FCL topologies which are more feasible or modifications of available topologies to increase feasibility. FCL introduces additional impedance to the system depending on the system operating conditions. It is not only reduces the fault current but. also effects on a number of power system related phenomena such as power losses, protection coordination, interrupting duty of switch gears, transient stability and voltage sag. This research work is mainly focus on application of Fault Current Limiter (FCL) to overcome this problem and facilitate the equipment safety.