SEL-T400L Time-Domain Line Protection
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SEL-T400L Time-Domain Line Protection Ultra-High-Speed Transmission Line Relay Traveling-Wave Fault Locator High-Resolution Event Recorder Major Features and Benefits The SEL-T400L is a state-of-the-art time-domain line protective relay operating within a few milliseconds for a wide range of fault and system conditions. The SEL-T400L incorporates fault locating with accuracy typically within one tower span. With only a handful of settings and preconfigured protection logic, the SEL-T400L is simple to apply, yet it supports a variety of applications and protection philosophies. ➤ Ultra-High-Speed Line Protection. Apply a traveling-wave line current differential scheme with a point-to-point fiber-optic channel to trip faults in 1–5 ms depending on the line length. Apply an incremental-quantity Zone 1 element with a 2–5 ms operating time without communication. Apply a permissive overreaching transfer trip scheme with any standard teleprotection channel using travelingwave and incremental-quantity directional elements operating in 0.1–3 ms. ➤ Versatile Applications. Apply the SEL-T400L to two-terminal overhead transmission lines, including series compensation, single- and dual-breaker terminations, and three-pole and single-pole tripping. ➤ Simple Configuration. Use preconfigured relay logic and set only a few protection settings without the need for extensive short-circuit studies. ➤ Accurate Fault Locating. Locate faults to the nearest tower. ➤ High-Resolution Oscillography. Record line currents and voltages with a 1 MHz sampling rate, storage for as many as 50 events, and a duration of 1.2 seconds per event. Schweitzer Engineering Laboratories, Inc.

Features and Benefits Traveling-Wave Differential Protection Scheme The traveling-wave differential (TW87) protection scheme uses current traveling waves (TWs) and a pointto-point fiber-optic channel to detect in-zone faults with operating times in the range of 1–5 ms depending on the line length. The TW87 scheme is independent from external time sources and provides internal synchronization of data over the communications channel. The TW87 scheme is suitable for series-compensated lines and can be used for single-pole tripping applications. The TW87 scheme uses traditional CTs and wiring....

Direct Transfer Trip Protection Scheme The direct transfer trip (DTT) scheme works with a fiberoptic Mirrored Bits communications port and uses phase-segregated signaling for single-pole tripping. DTT logic uses extra security to guard against undetected bit errors in the communications channel. Trip Logic A preconfigured trip logic processed ten times per millisecond allows for easy configuration of the relay for single-pole and three-pole tripping applications with a flexibility to accommodate different protection philosophies. Program the relay by using simple bit masks (lists) to...

nology used in the SEL-T400L has a field-proven accuracy in the order of about one tower span regardless of the line length. High-Resolution Oscillography The SEL-T400L provides time-stamped fault recording at a 1 MHz sampling rate with back-to-back recording capability, storage for as many as 50 events with a duration of 1.2 seconds per event, IEEE C37.111-2013 COMTRADE file format, and a user-configurable trigger. This 1 MHz, 18-bit recording capability allows analysis of high-frequency power system events including lightning strikes, breaker restrikes, and breaker transient recovery...

Protection Features The SEL-T400L provides two communications-based protection schemes (TW87 and POTT) and one incremental-quantity distance protection element (TD21). These time-domain elements work by using traveling waves and incremental quantities and use patented SEL technology. Incremental-Quantity Elements These elements use incremental quantities—the differences between the instantaneous voltages and currents and their one-cycle-old values. As such, the incremental quantities contain only the fault-induced components of voltages and currents. The SEL-T400L low-pass filters the...

The TD21 element is dependable for metallic faults in relatively strong systems. The element responds to resistive faults and in weaker systems, but with a slightly slower speed and reduced dependability. When applied in weak systems, the effective resistive coverage of the element increases as the source-to-line-impedance ratio (SIR) increases up to a point beyond which the element reach becomes gradually reduced. For high SIRs, the element automatically shuts down, favoring security over dependability. Owing to its operating principle, the TD21 element is not affected by CCVT...

seconds into the fault (see Figure 9). As a result, the relay responds to the TW activity during the few tens of microseconds following the first TW. Once asserted, the TW32 element is kept asserted for a short period of time to act as an accelerator for the dependable TD32 directional element in the POTT scheme. Integrated Torque Integrated Torque t TW32 TW32 Figure 9 Voltage and Current TWs for (a) a Forward Fault and (b) a Reverse Fault When applied with CCVTs, the TW32 element benefits from the stray capacitances across the CCVT tuning reactor and step-down transformer. These...

Tripping Schemes The SEL-T400L provides trip logic to conveniently route protection elements intended for tripping to the output contacts (see Figure 12). The logic allows for three-pole and single-pole tripping, responds to faults during the open-pole condition following a single-pole trip, and maximizes selectivity of single-pole tripping during evolving and intercircuit faults. The trip logic incorporates a current-reversal security logic and provides seal-in for the trip outputs using a timer and the ac current level. The logic incorporates communications-assisted tripping from the POTT...

Fault Locating The SEL-T400L incorporates an advanced travelingwave-based fault-locating algorithm with accuracy in the order of one tower span, allowing for reduced operating expenses and faster line restoration after a fault. Upon the assertion of a user-programmable trigger, including a preconfigured trip command, the relay executes a single-ended TW-based fault-locating algorithm and—if the point-to-point fiber-optic channel is available and operational—a double-ended algorithm. The faultlocating calculations are completed within 30 ms after the fault inception, i.e., before the circuit...