Impact of size and location of distributed generation on overcurrent relays in active distribution networks

Conventional distribution networks are mostly radial and are fed by central sources located at the transmission level. The power flow direction in these networks is unilaterally from sources to load feeders. In recent years, to meet the growth of demand, there has been an upward trend in the integration of distributed generation (DG) units to distribution networks. Although, the connection of DG units to the distribution network has many advantages, there are some undesirable impacts on the network operation and protection. After the interconnection of DG unit, short circuit levels will change. In addition, the power flow in some parts of the system may no longer be unilateral, resulting in the loss of coordination between relays. In this paper, the effect of the size and location of DG unit on the coordination of overcurrent (OC) relays in distribution networks will be investigated. The magnitude and the direction of short circuit currents for a sample network will be analyzed with and without DG unit. By changing the size and the location of DG units, the operation of OC relays and the coordination between them for upstream and downstream faults will be evaluated.