1.3
Date Code 20171021
Instruction Manual
SEL-421 Relay
Introduction and Specifications
Features
Out-of-Step Blocking and Tripping.
Select out-of-step blocking of distance ele-
ments 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 pro-
tection elements to quickly trip after the circuit breaker closes, protecting
maintenance personnel and substation equipment.
Frequency Elements.
Any of the six levels of frequency elements can operate
as either an underfrequency element or as an overfrequency element. The
frequency elements are suited for applications such as underfrequency load
shedding and restoration control systems.
Voltage Elements.
The relay offers as many as six undervoltage and six over-
voltage elements. Each of these 12 elements has two levels, for a total of 24
over- and undervoltage elements.
Fault Locator.
Efficiently dispatch line crews to quickly repair line problems.
Primary Potential Redundancy.
Multiple voltage inputs to the SEL-421 pro-
vide primary input redundancy. At loss-of-potential (LOP) detection, config-
ure 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 protec-
tion functions, but keep them separately available for monitoring and station
integration applications.
NOTE:
The SEL-421-4 has only one
100-line automation programming
block.
Automation.
Take advantage of enhanced automation features that include
programmable elements for local control, remote control, protection latch-
ing, 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, includ-
ing 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 as
many as 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 func-
tion 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-synchro-
nized state measurements across the system.
Oscillography and Event Reporting.
Record voltages, currents, and internal
logic points at as high as 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 set-
ting changes, power-ups, and selectable logic elements.
Summary of Contents for SEL-421-4
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