Integration of renewables into the distribution grid needs new software tools for coordination of protective relays

Traditional software tools developed for distribution system simulation and overcurrent protection coordination need to be revised to cope with the progressive integration of renewable distributed energy resources (DERs) in distribution grid to achieve better relay protection and coordination. Meanwhile, adoption of the microgrid concept results in certain problem for the protective relays using conventional techniques because of the downstream sources that can feed the fault and also the appreciable difference between the utility-grid connected mode and autonomous (islanded) mode. Traditional distribution grid protection is based on the overcurrent scheme with the flow of fault current from the upstream sources. However, the protection confronts with two main issues: firstly, the radial configuration of the distribution network is jeopardized by the distributed resources; and secondly the DERs have a stochastic nature and the contribution of fault current from the downstream is no longer a certain parameter that could be evaluated at the design stage. This paper analyzes the new requirements and strategies expected to be included in the traditional software tools in order to be applicable for the complex future distribution grids.