Common mistakes found in turn-key DER interconnection protection systems

The proliferation of distributed energy resources (DER) in the distribution grid has brought many challenges to the Distribution System Operators (DSO), as they have to ensure that the growing share of DER can be safely connect to the power grid and still maintain the network's safety, continuity of service and power quality requirements. An interconnection protection relay, placed between the grid and the DER facility, is an important part of maintaining safety requirements. In Portugal, external service providers working for the DER owner perform the installation and configuration of the interconnection relay. The DSO validates the interconnection protection hardware and wiring project, submitted by the DER owner, and provides the adequate relay settings. In the end, the DSO is present at the commissioning stage making sure the relay behaves as expected and may seal it to avoid any unauthorized change. Even though this workflow has proven its benefits, EDP Distribuição (EDPD) has found some recurring mistakes in the installation and configuration of the interconnection relays that are not prejudicial to the network but often lead to many undesirable trips thus reducing the energy produced by the DER and increasing maintenance costs. In this paper, authors will present and discuss the most common mistakes made by external service providers in Portugal when installing and configuring the interconnection protection relays.