A New Second Central Moment-Based Algorithm for Differential Protection in Micro-Grids

There are different definitions for Smart Grid, one of them is: Smart Grids is that it employs a wide variety of distributed energy resources (DER). In such conditions, the increasing local generation requires a new type of approach for protection. Ensuring the function of a relay to satisfy the requirements of the development of the smart grid and perform the protection task with high reliability, involves solving different technical aspects. In order to remove the fault with a minimum area of interruption, it requires the setup of multiple protection relays and their technical coordination. In order to meet the above requirements, protection devices based on various hardware platforms, different techniques and the on-site operational management of these devices have been proposed. An interesting feature proposed for the Smart Grid is self-healing. This means that the system is capable of continuing the power supply after any kind of disturbances. Self-healing is, in fact, a broad concept including the stability of transmission grids, but here the focus is on the protection of MV distribution networks. In this context, one way to achieve the self-healing functionality is to switch over to island operation in case of a fault in some parts of the network. The successful use of the local generation for achieving controlled island operation in some fault cases requires the use of suitable telecommunication between different parts of the system. In addition to this, there is a need to adapt the protection configuration to the system state. Especially critical in this respect is the power generated by the local sources and the loading in various parts of the network. Depending on the load/generation balances the size of suitable islands to be used in fault cases may be different at different times.