Utility-accessible external disconnect switch suppression in PV microgeneration: Brazilian scenario

Utility-Accessible External Disconnect Switch (EDS) is an AC switch used in electric power systems to disconnect Distributed Energy Resources (DER) from the main grid during maintenance. The EDS utilization is intended for line worker safety, since it is currently the only mechanism to ensure galvanic disconnection between DER and distribution network. Frequency inverters used in DER has a built-in switch, composed by a relay, called Integrated Disconnect Switch (IDS), and protective functions (anti-islanding, under/over-voltage and -frequency algorithms). In some countries, the EDS were recently considered unnecessary and redundant for PV systems, since the IDS provide DER galvanic disconnection when it detects utility outage or abnormal conditions. Moreover, the EDS suppression reduces the DER overall cost. The elimination of the EDS from PV low power installations was recently in discussion in Brazil. This paper aims to present a study on the reasons why the EDS should not be eliminated from PV grid-tied low-power installations. The existing standards, network maintenance procedures and the EDS cost/effectiveness are discussed.