The SEL-T401L is a new transmission line relay that combines time-domain technology and phasor-based protection in a single device. The new line-monitoring feature makes it the only relay capable of detecting and locating incipient faults. In addition, the SEL-T401L features traveling-wave-based fault-locating methods, location-dependent autoreclose cancel logic, and high-resolution transient recording. Suitable for a wide range of applications, the SEL-T401L offers an opportunity to reset the complexity of line protection applications with simple protection philosophies and a reduced setting count.
The combination of time-domain technology and a complete suite of phasor-based protection functions makes the SEL-T401L an ideal choice for state-of-the-art transmission line protection. The time-domain protection elements and schemes operate in 1–5 ms, and the distance protection elements operate at subcycle speed. The relay is well suited for lines near nonstandard generators, such as wind generators or inverter-based sources; in low-inertia systems with HVdc links; and in systems with series compensation.
The new line monitor feature can detect and locate low-energy transient events, which are indicators of potential future faults. The line monitor will detect, locate, tabulate, and alarm for discharge across dirty or damaged insulators, incipient cable faults, discharge from encroaching vegetation, and other events not accompanied by protection operation.
The SEL-T401L includes single- and double-ended traveling-wave-based fault-locating methods that locate faults within one tower span. It also includes single- and double-ended impedance-based methods for a reliable and complete solution.
The SEL-T401L includes built-in adaptive location-dependent autoreclose cancel logic. Allow or inhibit autoreclosing based on the accurate real-time fault location. Inhibit reclosing for faults on the cable sections of a hybrid line, near airports, along fire-prone stretches of an overhead line, or in areas where humans or animals are present.
The SEL-T401L provides ultra-high-resolution voltage and current recording with a 1 MHz sampling rate and an 18-bit resolution. You can record and analyze high-frequency transients, such as traveling waves from faults, switching events, breaker re-ignition, breaker restrikes, and self-extinguishing faults.
The SEL-T401L design achieves the right balance between the need to customize the relay to suit your specific requirements and the advantages of simplicity, workforce efficiency, and avoidance of human errors. The SEL-T401L is as flexible as it needs to be to accommodate a variety of applications, yet it simplifies choices in other areas.