PCS-221S The merging unit is used to sample the analog AC values and transmit the sampled values (SV) to the protection device, bay control unit (BCU) or energy meters via optical communication links based on IEC 61850-9-2 and IEC 61869-9 protocol. PCS-221S can also be used to control the primary switching equipment, i.e.: Circuit Breaker (CB), Disconnector (DS), Earthing Switch (ES) in digital substations of all voltage levels. It supports real-time GOOSE communication and can perform CB/DS/ES tripping and closing via protection devices and BCUs. It can receive binary input signals of primary equipment (CB/DS/ES) simultaneously. It can meet the GOOSE tripping requirement in point-to-point mode or network mode.