html{display:none} SEL-T400L Time-Domain Line Protection | Schweitzer Engineering Laboratories


Time-Domain Line Protection

Apply the SEL-T400L Time-Domain Line Protection for ultra-high-speed protection of transmission lines. With the breakthrough time-domain technology of traveling waves and incremental quantities, the SEL-T400L trips securely in as fast as 1 ms. The relay records events with a 1 MHz sampling rate, locates faults to the nearest tower, and monitors the line for incipient faults, recurring faults, or incipient cable faults. Adding the SEL-T400L to your line protection system can dramatically reduce your fault-clearing time and let you achieve the many benefits associated with speed.

Starting At

$12,000 USD

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Ultra-High-Speed Tripping With Security—The SEL-T400L features a traveling-wave differential scheme (TW87) over a dedicated point-to-point fiber channel; an incremental-quantity distance element (TD21) and a POTT scheme with traveling-wave (TW32) and incremental-quantity (TD32) directional elements over a digital or an analog protection channel. You can achieve 1–5 ms trip times, depending on the channel, line length, and system conditions.

Simplicity—Requiring only a few protection settings, the SEL-T400L is easy to learn, easy to apply, and easy to set. The relay settings require only very basic short-circuit studies, and the relay settings are greatly resilient to power system evolution and changing short-circuit levels.

High-Fidelity Recording—The SEL-T400L provides 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 reignition, and self-extinguishing faults. The SEL-T400L also streams time-stamped Fast Time-Domain Values (FTDV). Contact SEL to obtain a detailed format description as well as tools to experiment with this advanced SEL-T400L functionality.

Unparalleled Fault Locating—The SEL-T400L includes traveling-wave fault-locating methods that work with or without communications. The SEL-T400L has a field-proven accuracy of about one tower span. The double-ended fault location result is available within a few tens of milliseconds, allowing the SEL-T400L to control autoreclosing depending on the location of the fault (such as in applications on lines with cable sections). The SEL-T400L also includes a line monitoring function, which can be used for condition-based line maintenance to prevent line faults and to discover weak spots along the line.

Testing Made Easy—Requiring only a few protection settings, the SEL-T400L is easy to commission. You can apply any standard relay test set for testing the TD21 distance and TD32 directional elements or use the SEL-T4287 Traveling-Wave Test System for end-to-end testing of the TW87 scheme, the TW32 element, and the traveling-wave fault locator.

Event Playback—You can test the protection and fault-locating functions without a relay test set by using the built-in event playback function and events recorded in the field or simulated using electromagnetic transient programs. With the event playback function, you can trigger a playback test in multiple relays based on time for end-to-end testing of the SEL-T400L protection schemes and multi-ended fault locators.


    1. 1

      USB 2.0 port for local engineering access

    2. 2

      Display for viewing metering, event, fault location, and relay status information 

    3. 3

      Simple HMI navigation

    4. 4

      Slide-in label pocket and LED targets for viewing trip cause, fault type, and basic relay status

    5. 5

      Large slide-in label pocket for diagrams or asset information 

    1. 1

      Six trip-rated high-speed outputs for single-pole tripping of two breakers

    2. 2

      Alarm output

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      Five inputs with a common terminal

    4. 4

      IRIG-B time input

    5. 5

      Three fiber-optic ports for multiplexed or direct protection signaling (SEL MB8 or IEEE C37.94)

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      1 Gbps small form-factor pluggable (SFP) Ethernet port for engineering access and SCADA

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      SFP fiber-optic port for ultra-high-bandwidth protection signaling over direct fiber

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      Breaker 1 and 2 current inputs

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      Line voltage

    10. 10

      Power supply



Protection Applications
Apply the SEL-T400L to a variety of line and system configurations, including:

  • POTT and direct transfer tripping (DTT) protection schemes for two-, three-, and four-terminal lines over a digital channel (select SEL Mirrored Bits encoding or IEEE C37.94 encoding), analog channel (use SEL-2500 series I/O modules), or direct-fiber channel (use wavelength division multiplexing to share fibers).
  • TW87 protection scheme for two-terminal lines with a provision for unmeasured taps, over a direct-fiber channel. (Use wavelength division multiplexing to share fibers.)
  • Underreaching directly tripping distance element.
  • Single-pole tripping.
  • Series-compensated lines.
  • Lines with line-side and bus-side reactors.
  • Hybrid lines with overhead and underground cable sections.
  • In-line CTs and breaker CTs in dual-breaker applications with per-breaker current measurement.
  • High-speed trip-rated outputs for two breakers and single-pole tripping.

Hassle-Free Installation
Use the SEL-T400L with standard control cables and wiring to connect to conventional current and voltage transformers, including coupling capacitor voltage transformers (CCVTs), and directly to breaker trip-coil circuits. The relay uses current traveling waves that are adequately measured with standard CTs and cabling. The relay uses the very first voltage traveling wave in the optional TW32 directional element, and this wave is reproduced correctly by many CCVTs, allowing good TW32 dependability. You can select either SEL MB8 encoding for signaling local SEL relays and SEL I/O devices for breaker failure protection and autoreclose control applications or IEEE C37.94 encoding for signaling a remote SEL-T400L over a compliant multiplexer for POTT, DTT, double-ended traveling-wave fault locating (DE-TWFL), autoreclose cancel logic, and line monitoring applications. The SEL-T400L provides a simple communications means to access relay metering data and records. These protocols include SEL protocols for ease of integrations with SEL systems, DNP3 over Ethernet for interconnecting with DNP-based SCADA systems, and generic Ethernet file transfer methods for ease of integration with Ethernet-based substation automation systems.

Relay Configuration and Settings
Designed with simplicity in mind, the SEL-T400L uses simple multiple-choice user preferences to accommodate a wide array of applications without the need to write custom logic equations. The protection elements and schemes have very few or no settings at all in addition to the customary enable and overcurrent supervision settings. The majority of protection settings involve nameplate data, such as current and voltage transformer ratios, line parameters, nominal voltage, or system frequency and phase rotation. These settings are easy to set and do not need to be reevaluated as the power system evolves and the short-circuit levels change.

Fault-Locating Applications
Trigger fault locating for line faults from the SEL-T400L protection or from external relays in redundant protection applications or in standalone fault-locating applications. SEL-T400L fault-locating highlights include:

  • Fault locating for two-terminal lines that is accurate to a single tower span based on traveling waves from one or both ends of the line
  • Double-ended traveling-wave fault locating for nonhomogeneous hybrid lines with overhead and underground cable sections
  • Double-ended fault-locating result that is available in milliseconds, allowing the SEL-T400L to control autoreclosing based on the location of the fault
  • Built-in fallback to single- and double-ended impedance-based fault-locating methods for dependability of fault locating during faults at the voltage zero crossing
  • Support for off-line traveling-wave fault locating for multiterminal lines

Line Monitoring
Monitor the line for incipient faults, recurring faults, or incipient cable faults. Obtain a location-tabulated event count to detect low-energy activity and faults along the line. Prevent faults by selectively cleaning or replacing insulators, trimming vegetation, improving antigalloping solutions, applying line spacers, or improving lightning protection. Line monitoring works over a direct fiber-optic channel or a 64 kbps IEEE C37.94-encoded multiplexed channel.

Digital Fault-Recording Applications
SEL-T400L recording highlights include:

  • High-fidelity (1 MHz, 18-bit) time-stamped sampling with the frequency response up to about 400 kHz
  • Programmable trigger for standalone recorder applications
  • Recording duration of up to 1.2 seconds per record
  • Storage for up to 50 1.2-second events
  • Back-to-back recording capability for the total length of up to 3.6 seconds
  • Local voltages and individual breaker currents
  • Time-aligned remote voltages and line currents if the dedicated point-to-point fiber channel is used
  • Ultra-high-resolution records (1 MHz analogs) for analysis of power system events and of traveling-wave protection and fault-locating functions
  • High-resolution records (10 kHz analogs and digitals) for analysis of protection functions
  • IEEE COMTRADE (2013 version) file format
  • TCP/IP File Transfer Protocol (FTP) over a Gigabit Ethernet port for fast access to the large record files
  • Streaming FTDV over a Gigabit Ethernet port for wide-area high-fidelity event recording and continuous monitoring

Minimum QuickSet Version

Product Revision Z Number Minimum Software Version
SEL-T400L R103-V0 004
SEL-T400L R102-V0 003


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Latest Firmware Versions

There are no firmware versions available for this product.

Product Revision Firmware ID Date Available Serial Number
SEL-T400L R104-V2 SEL-T400L-R104-V2-Z005004-D20210930 10/15/21 ~1212880001

The Firmware IDs for older versions of the firmware can typically be found in Appendix A of the instruction manual.

Minimum QuickSet Version

Product Revision Z Number Minimum Software Version
SEL-T400L R103-V0 004
SEL-T400L R102-V0 003

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