SEL Relays in the Yard

Digital relays installed in appropriately rated outdoor cabinets in the substation yard are wired to primary equipment using conventional field-wiring practices and potentially also connected to merging units using digital communications. Fiber-optic cables are used to carry communications between the relays and the control house.

Moving relays to the substation yard is as simple as changing the location of the relay panel. Existing protection designs, engineering methods, and configuration tools do not need to change. Engineering and technical support remains the same, with the same tools and methods, as well as some service performed in the yard similar to servicing merging units.

This solution reduces the amount of copper wiring necessary for the devices to acquire data from instrument transformers, sensors, and actuators. Marshalling cabinets can be eliminated, along with the associated copper wiring.

Relays from SEL are designed to meet and exceed long-standing protection device design and manufacturing standards. They support necessary status and diagnostics for process bus and station bus communications, including data stream monitoring, PRP monitoring, and Ethernet monitoring. Relays also collect power system data at high frequencies, which is essential for enhanced protection and monitoring functions.

Relays in the substation yard often need to collect more than current and voltage measurements to perform protection actions. SEL relays and other devices, like the SEL-2600 RTD Module, collect and digitize ancillary data, such as temperature, alarms, and more to supplement the current, voltage, and status signals from primary equipment. SEL devices connect to various protection, control, and monitoring sensors and actuators, and they support traditional CT/PT, Rogowski coil, and digital message inputs.

When installed in the yard, additional I/O devices, such as the SEL-2440 DPAC or SEL-2600, communicate with relays using direct connections, process bus communications, or station bus communications.

Several important factors must be considered when designing and implementing a system with relays installed in cabinets in the substation yard.

Be sure to verify that the devices you intend to use have the resilience necessary to maintain availability and accurate operation under local conditions.

All SEL-certified devices undergo rigorous functional and environmental tests to ensure that they will operate in the most challenging environments. SEL devices withstand temperatures from –40° to +85°C (–40° to +185°F), as well as electrical surges and other harsh conditions. An optional conformal coating for circuit boards adds an extra level of protection against contaminants in extreme environments.

By using fiber-optic communications cables between relay cabinets in the yard and equipment in the control house, relays may be connected to a station bus network for SCADA, commanded control operations, data collection, and engineering access. Relays may also use fiber-optic cables to connect to process bus networks or to exchange GOOSE messages and time synchronization.

Relays in the substation yard may be directly connected to one another or networked using routable or non-routable communications protocols as needed. This capability allows substations to integrate relays installed in the yard with process bus and station bus systems using a variety of protocols, such as DNP3, FTP, Telnet, HTTP, IEC 61850 MMS and GOOSE, as well as IEC 61158 EtherCAT®, synchrophasors, and SEL-2600 RTD communications. (EtherCAT® is a registered trademark and patented technology, licensed by Beckhoff Automation GmbH, Germany.)

Cybersecurity is a vital consideration in process bus systems. However, because operational technology and information technology systems have different purposes, the cybersecurity solutions for one system may not be the most appropriate for another.

Secrecy Methods Reduce Availability

Network connections that are not engineered to maintain privacy often require coordinated secrecy methods like TLS within each device to obscure data, generally by encryption, making them unreadable to other devices and unauthorized users. This solution is undesirable in secondary systems because the additional processing load and time required to encrypt and decrypt data can slow protective action. Encryption also makes data unavailable to engineers, technicians, other devices, and systems that lack the appropriate decryption capabilities. 

In addition, the increased frequency of firmware updates required to stay current with secrecy technologies poses a serious obstacle for maintaining system availability, requires that devices be updated simultaneously, and introduces new supply chain and personnel vulnerabilities. Unintended consequences that affect protection reliability include device down time during firmware upgrades to address security vulnerabilities and a lack of communications among devices until they are all upgraded to the same firmware version. 

As part of a digital secondary system implementation, a relays-in-the-substation-yard solution is as simple or sophisticated as an application demands, but many important factors must be considered in designing the system.

Partner with SEL Engineering Services to create a turnkey solution that addresses the needs of your system and puts you in control. Our expert engineers provide thorough training in all products applied in a solution, ensuring that you can achieve your operational goals once a system is in place.

We've collaborated closely with our customers since the company was founded over 40 years ago—a major reason why we’re North America’s most trusted provider of protective relays and ranked #1 by international utilities in price, service, and support.