Tdworld 11358 Digital Substations

Sampled Values Solution with Protection Functions Integrated into the Merging Unit

Nov. 21, 2017
Create a robust, flexible, and interoperable IEC 61850-9-2 protection system that saves copper, money, time, and lives.

Schweitzer Engineering Laboratories, Inc. jas released a new solution for digital secondary systems that uses IEC 61850-9-2 Sampled Values (SV) data streams for protection, monitoring and control. Digital secondary systems eliminate the need to run high-energy cables into the control house and reduce the use of copper cabling.

The new SEL-401 Protection, Automation, and Control Merging Unit and SEL-421 Protection, Automation, and Control Merging Unit digitize analog signals from primary equipment and transmit them to relays in the control house via an Ethernet network. The system uses precise time synchronization provided by IRIG-B or the Precision Time Protocol (PTP). 

SEL merging units have integrated, local protection that works even if communications are lost between the merging unit and the relay. They can be paired with SV-supported relays (such as the SEL-421 Protection, Automation, and Control System) or with other devices that are IEC 61850-9-2-compliant, providing interoperability in user networks. SEL will be adding SV technology to the SEL-451 Protection, Automation, and Bay Control System; the SEL-487B Bus Differential and Breaker Failure Relay; and the SEL-487E Transformer Protection Relay.

“SV is one of three digital secondary system solutions that SEL offers,” said Greg Rzepka, R&D engineering director. “Utilities around the world place SEL relays out in the yard to reduce copper and installation costs while increasing safety. Customers apply SEL Time-Domain Link (TiDL™) technology for a cybersecure, point-to-point solution that is simple to apply, with no network engineering or external time reference required. With an IEC 61850-9-2 Sampled Values solution joining the SEL portfolio, users have yet another option for modernizing their substations.”

To learn more about SEL digital secondary system technologies, visit

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