U.1.3
Date Code 20090715 User’s Guide SEL-421 Relay
Introduction and Specifications
Features
Out-of-Step Blocking and Tripping. Select out-of-step blocking of distance
elements or out-of-step tripping during power swings. The SEL-421
includes multizone elements and logic for detection of an out-of-step
condition.
Switch-Onto-Fault. Relay switch-onto-fault (SOTF) logic permits specific
protection elements to quickly trip after the circuit breaker closes,
protecting maintenance personnel and substation equipment.
Fault Locator. Efficiently dispatch line crews to quickly repair line
problems.
Primary Potential Redundancy. Multiple voltage inputs to the SEL-421
provide primary input redundancy. At loss-of-potential (LOP)
detection, configure the relay to use inputs from an electrically
equivalent source. Protection remains in service without
compromising security.
Dual CT Input. Apply with ring bus, breaker-and-a-half, or other two-
breaker schemes. Combine currents within the relay from two sets of
CTs for protection functions, but keep them separately available for
monitoring and station integration applications.
NOTE: The SEL-421-1 and the
SEL-421-2 have only one 100-line
automation programming block.
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, Sequential Events Recorder
(SER) reports, breaker monitor, relay summary event reports, and time
synchronization. Use expanded SEL
OGIC control equations with math
and comparison functions in control applications. Incorporate up to
1000 lines of automation logic to speed and improve control actions.
Monitoring. Schedule breaker maintenance when accumulated breaker
duty (independently monitored for each pole of two circuit breakers)
indicates possible excess contact wear. Electrical and mechanical
operating times are recorded for both the last operation and the average
of operations since function reset. Alarm contacts provide notification
of substation battery voltage problems (two independent battery
monitors) even if voltage is low only during trip or close operations.
Comprehensive Metering. View metering information for Line, Circuit
Breaker 1, and Circuit Breaker 2. SEL-421 metering includes
fundamental and rms metering, as well as energy import/export,
demand, and peak demand metering data. Synchrophasor data can be
used for time-synchronized state measurements across the system.
Oscillography and Event Reporting. Record voltages, currents, and
internal logic points at up to 8 kHz sampling rate. Phasor and
harmonic analysis features allow investigation of relay and system
performance.
Sequential Events Recorder (SER). Record the last 1000 entries, including
setting changes, power-ups, and selectable logic elements.
High-Accuracy Time Stamping. Time-tag binary COMTRADE event
reports with real-time accuracy of better than 10 µs. View system state
information to an accuracy of better than 1/4 of an electrical degree.
Courtesy of NationalSwitchgear.com
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