SEL-421-4, -5 Protection and Automation System
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SEL-421-4, -5 Protection and Automation System High-Speed Line Protection, Automation, and Control System Major Features and Benefits The SEL-421-4, -5 Protection, Automation, and Control System combines high-speed distance and directional protection with complete control for a two-breaker bay. ➤ Protection. Protect any transmission line by using a combination of five zones of phase- and grounddistance and directional overcurrent elements. Select Mho or Quadrilateral characteristics for any phase or ground-distance element. Use the optional high-speed elements and series compensation logic to optimize protection for critical lines or seriescompensated lines. Use the ACSELERATOR QuickSet® SEL-5030 Software (a graphical user interface) to speed and simplify setting the relay. Patented Coupling Capacitor Voltage Transformer (CCVT) transient overreach logic enhances the security of Zone 1 distance elements. Best Choice Ground Directional Element® logic optimizes directional element performance and eliminates the need for many directional settings. ➤ Automation. Take advantage of enhanced automation features that include 32 programmable elements for local control, remote control, protection latching, and automation latching. Local metering on the large format front-panel Liquid Crystal Display (LCD) eliminates the need for separate panel meters. Use serial and Ethernet links to efficiently transmit key information, including metering data, protection element and control I/O status, IEEE C37.118 Synchrophasors, IEC 61850 GOOSE messages, Sequential Events Recorder Schweitzer Engineering Laboratories, Inc. (SER) reports, breaker monitor, relay summary event reports, and time synchronization. Use expanded SELOGIC® control equations with math and comparison functions in control applications. Incorporate as many as 1000 lines of automation logic (depending on the model) to speed and improve control actions. ➤ Synchrophasors. Make informed load dispatch decisions based on actual real-time phasor measurements from SEL-421 Relays across your power system. Record streaming synchrophasor data from SEL-421 Relays for system-wide disturbance recording. Control the power system by using local and remote synchrophasor data. ➤ Digital Relay-to-Relay Communications. Use MIRRORED BITS® communications to monitor internal element conditions between relays within a station, or between stations, by using SEL fiber-optic transceivers. Send digital, analog, and virtual terminal data over the same MIRRORED BITS channel. Receive synchrophasor data from as many as two other devices transmitting IEEE C37.118-2005 format synchrophasors at rates as high as 60 messages per second. The SEL-421 time-correlates the data for use in SELOGIC control equations.

► Primary Potential Redundancy. Multiple voltage inputs to the SEL-421 provide primary input redundancy. Upon loss-of-potential (LOP) detection, the relay can use inputs from an electrically equivalent source connected to the relay. Protection remains in service without compromising security. ► Parallel Redundancy Protocol (PRP). This protocol is used to provide seamless recovery from any single Ethernet network failure, in accordance with IEC 62439-3. The Ethernet network and all traffic are fully duplicated with both copies operating in parallel. ► Ethernet Access. Access all relay...

ANSI NUMBERS/ACRONYMS AND FUNCTIONS Phase and Ground Distance Synchronism Check Directional Power Dual Breaker Failure Overcurrent Directional Overcurrent Out-of-Step Block/Trip Single-/Three-Pole Reclosing SEL Mirrored Bits® Communications Event Reports Operator Interface Expanded SELOGIC® Control Equations High-Accuracy Metering Sequential Events Recorder Time-Domain Link Remote Data Acquisition Breaker Wear Monitor Load Encroachment Fault Locator Station Battery Monitor 1 Copper or Fiber Optic * Optional Feature Figure 1 Functional Diagram The SEL-421 contains all the necessary...

Subcycle Tripping Times Using Optional High-Speed Elements Standard-Speed Elements High-Speed Elements 20% 40% 60% 80% Fault Location as % of Reach Setting Figure 2 20% 40% 60% 80% Fault Location as % of Reach Setting Single-Phase-to-Ground Faults Standard-Speed Elements High-Speed Elements 60% 80% 20% 40% Fault Location as % of Reach Setting Figure 3 60% 80% 20% 40% Fault Location as % of Reach Setting Phase-to-Phase Faults Standard-Speed Elements High-Speed Elements 60% 80% 20% 40% Fault Location as % of Reach Setting Fault Location as % of Reach Setting Figure 4 Three-Phase Faults The...

As an optional addition to the standard distance elements, there are three zones (either three forward, or two forward and one reverse) of high-speed distance elements. These high-speed elements use voltage and current phasors derived from a fast half-cycle filter to provide subcycle tripping times. Settings are automatically associated with the standard element zone reach; no additional settings are required. The SEL-421 includes optional series-compensated line logic and polarizing to prevent overreach of the Zone 1 distance element resulting from the series capacitor transient response....

Communications-Assisted Tripping Schemes The SEL-421 is the ideal relay for use in transmission pilot-based tripping schemes. Use Mirrored Bits communications with SEL fiber-optic transceivers for 3-6 ms relay-to-relay transmission time. Among the schemes supported are the following: ► Permissive Overreaching Transfer Tripping (POTT) for two- or three-terminal lines ► Directional Comparison Unblocking (DCUB) for two- or three-terminal lines ► Directional Comparison Blocking (DCB) Use the SEL control equation TRCOMM to program specific elements, combinations of elements, inputs, etc., to...

Loss-of-Potential (LOP) Logic Supervises Directional Elements CT caused by trapped flux, high-speed detection of circuit breaker opening is achieved. If breaker failure is initiated on all circuit breaker trips, this feature is essential. A 5/8-cycle reset reduces coordination times, improving stability. The SEL-421 includes logic to detect a loss-of-potential caused by failures such as blown fuses, which can cause an incorrect operation in distance and directional elements. Simple settings configure the LOP logic to either block or force forward ground and phase directional elements under...