html{display:none} Transmission | Schweitzer Engineering Laboratories


If you have transmission system challenges that you need to solve—no matter how complex—SEL is ready with the products and expertise you need.

Transmission hero

Our solutions focus on the first principles of protection, augmented by automation and monitoring capabilities, wide-area communications, and industry-leading traveling-wave technology.

SEL is recognized as North America’s most trusted relay supplier and a world leader in transmission protection—a position of trust we’ve earned over decades of dedicated service to the electric power industry. We bring industry-leading reliability and support to customers around the world.

Line Protection

Our distance protection and line current differential relays feature advanced protection logic that increases reliability and allows flexible application. And SEL relays with time-domain and traveling-wave technology are setting new standards for fast, secure tripping decisions and precise fault location.

Distance Protection

Advanced SEL protection logic allows you to securely apply distance protection elements on heavily loaded transmission lines and improve system stability during power swings.

Line Current Differential Protection

Use line current differential protection for long extra-high-voltage lines, complex systems where distance protection alone is inadequate, and primary lines when connecting wind farms to the utility grid.

Time-Domain Line Protection

SEL time-domain technology sets new standards for accuracy, speed, reliability, and security. With their incremental quantities and traveling-wave protection elements, time-domain-enabled SEL relays simplify protection schemes and enable faster, more secure tripping.

Traveling-Wave Fault Location

Locate faults with speed and accuracy. The traveling-wave technology in SEL-T400L, SEL-T401L, and SEL-411L relays pinpoints the source of a fault to within a single tower span, so you can dispatch crews where they’re needed and make repairs quicker than ever.

Bay Control and Substation Integration

SEL provides complete monitoring and control solutions for all of your mission-critical substation equipment, including double breakers, reclosing, breaker failure, and auxiliaries such as air break switches, grounding switches, and more.

Digital Secondary System (Digital Substation) Solutions

SEL digital secondary system solutions—commonly called digital substation solutions—help protect and control a substation’s primary equipment. This type of system transmits data via fiber-optic cables from remote field modules in the yard to relays in the control house. Pick the solution that fits your application.

TiDL Technology: An SEL Innovation

Time-Domain Link (TiDL) technology is an innovative, protection-centered solution engineered with simplicity in mind. It uses a point-to-point architecture, secure direct fiber connections, and built-in time synchronization, making it easy to implement with no network engineering required.

Sampled Values Technology

SEL Sampled Values (SV) solutions combine protection in the merging units with the flexibility of IEC 61850-9-2 communications. It is a communications-centric, standard-compliant solution that uses a point-to-multipoint Ethernet-based network to transmit data.

Monitoring and Automation

Control and optimize every aspect of power system protection and operation to improve performance and resiliency.

See Monitoring and Automation Solutions

Synchrowave Operations: The Next Step in Situational Awareness

Visualize and monitor your entire transmission system—so you never have to wonder what’s happening with mission-critical functions and equipment. SEL Synchrowave Operations software works seamlessly with all SEL transmission protection devices to turn the advanced data they collect into information you can use.

More About Synchrowave Operations Software


SEL University, Conferences, Tradeshows, Seminars

SEL meets your immediate and long-term workforce education needs by offering SEL University courses, seminars, conference presentations, and attending tradeshows. SEL University complies with the ANSI/IACET Standard, which is recognized internationally as a standard of excellence in instructional practice. As a result of this accreditation, SEL University is authorized to issue the IACET CEU.

SEL Solutions in Action


TOUA featured

Lighting up the Desert Nation

In the Sonoran Desert, intense summer heat and sudden microburst storms caused repeated power outages for TOUA, the Tohono O’odham Utility Authority—until they modernized their system with SEL-T400L relays. See how SEL time-domain technology and traveling-wave fault location answered the challenge of electric power transmission in this unforgiving environment.

GSE featured

Republic of Georgia Enters New Era of Reliable Energy

See how SEL helped the country of Georgia stabilize its transmission grid with an emergency control system, ending decades of nationwide blackouts—and then implemented a remedial action scheme (RAS) that ensures reliable delivery of electric power and provides for future growth.

Customer Service

A Modern WAN—Simple, Economical, Elegant


SEL Brings NamPower Into the 21st Century

Furnas Featured

Cool Solutions Solves Brazil's Heat Challenge


Pend Oreille Benefits From Innovative RTU Upgrade Strategy

Questions? Contact Us!

We’re happy to answer all your questions and help develop the best solution for your needs.

Contact Engineering Services


Unbeatable Support

SEL support teams are stationed in regional offices around the world and staffed with application engineers who are experts in our products and in power system applications.

Technical support for SEL-manufactured devices is always free. No matter how often you need to call or how long your SEL products have been in service, you’ll reach an SEL expert who can provide the service and support you need.

Our cybersecurity team is always ready with the information and resources needed to keep your OT networks and critical systems secure and working effectively. Cyber services support contracts can include incident response, audits, system hardening, and more, depending on your anticipated needs.