SEL-T400L Protective Relay


Discover the world's fastest transmission line relay

Millisecond Tripping

The SEL-T400L Time-Domain Line Protection breaks the speed barrier of phasor-based relays and trips in single milliseconds before the fault current even reaches the first peak. Designed for impeccable security, the relay provides high-speed tripping with novel protection principles based on traveling waves and incremental quantities.

Refreshing Simplicity

Having only a few settings makes the SEL-T400L simple to learn, simple to set, and simple to apply.

Megahertz Recording

The SEL-T400L fault recorder captures voltages and currents every microsecond with 18 bits of resolution. This breakthrough recording performance opens up a whole other world for power system analytics. Now you can capture and analyze breaker restrikes, partial breakdown of insulators, self-extinguishing faults, and more.

Nearest-Tower Fault Locating

The SEL-T400L routinely locates faults to within one tower span. It distinguishes faults on overhead line sections from faults in underground cable sections and controls autoreclosing accordingly. Plus, the relay works with information from one or both ends of the line.


The SEL-T400L is a quantum leap in line protection performance. Using traveling waves and incremental quantities, the SEL-T400L breaks the phasor-based relays’ speed barrier by tripping in as fast as 1 ms. That’s ten times faster than today’s typical protection speeds. When you’re protecting personnel, expensive equipment, and the power system, every millisecond counts.

Speed. Security. Simplicity. SEL-T400L

Breakthrough time-domain and traveling wave technologies make the SEL-T400L the fastest, most secure relay in the world.

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