Comparative Analysis of Technical Solutions for Secondary Systems in Substations with a “Breaker-and-a-Half” Scheme

Based on their purpose and functions within the power system, substations in the Republic of Bulgaria are classified into system substations, distribution substations, and transformer stations. System substations connect different parts of the power system as well as two different power systems. Because system substations are supplied by transmission power lines and handle large power flows, they have increased reliability requirements. To meet these requirements, design solutions are implemented, which include electrical scheme configurations for switchyards with multiple connections, such as the “breaker-and-a-half” scheme. The technical solutions for measurement systems, operational power supplies, control, protection, signaling, and communication can be collectively summarized as secondary system. This paper will specifically examine these technical solutions, taking into account the advantages and disadvantages of the “breaker-and-a-half” scheme.