**5.2 Over current protection**

Over current protection that has been in use for conventional distribution system protection requires some modifications to be made so that it can be used for the protection of mesh connected micro grid with DERs.

In order to understand the proper functioning of the overcurrent protection, let us consider a simple structure of a micro grid shown in **Figure 1**. In general this can be divided into four zones namely MV feeder and busbar protection zone (Z1), transformer protection zone (Z2), LV feeder protection zone (Z3) and micro grid protection zone (Z4) as shown in **Figure 2**.

Based on the location of fault with respect to DER, they can be classified into external (in Z1 and Z2) and internal faults (in Z3 and Z4). If the CB1 is open the micro grid is in islanded mode and if it is closed it is in grid connected mode [18].
