A review of transient effects of different types of distributed generation units on overcurrent protection system

Adding distributed generation (DG) units to the passive electricity networks causes several significant changes in their characteristics like power flow direction, voltage profile and short circuit level. Therefore the currently used control and protection strategies can no longer work properly and they have to be revised and modified. One of the most important issues is protection problem. For a reliable and efficient protection system, both transient and steady state effects of DGs on fault current should be considered. In this paper the exact model of three different types of DGs with different grid interfaces (PSMG with full size converter, DFIG with partial size, commonly met on Belgian grids, and directly connected IG) including power electronics and control systems, are presented. After that, the fault currents generated by different size and location of DGs are compared with those one which are produced by ideal model of DGs in the same condition. The PSCAD software is used for simulation of transient contribution of DG in fault current, in an assumed medium voltage grid.