1.2
SEL-421 Relay Instruction Manual Date Code 20171021
Introduction and Specifications
Features
Features
The SEL-421 contains many protection, automation, and control features.
Figure 1.1 presents a simplified functional overview of the relay.
SEL-421 features include the following:
NOTE: The SEL-421-4 does not
provide series-compensated line
protection logic.
Superior Protection. Combine five zones of phase-distance and ground-dis-
tance elements with directional overcurrent elements. Patented Coupling
Capacitor Voltage Transformer (CCVT) transient overreach logic enhances
Zone 1 distance element security. The Best Choice Ground Directional Ele-
ment optimizes directional element performance and eliminates many set-
tings. Additional logic prevents Zone 1 overreach on series-compensated
lines.
NOTE: The SEL-421-4 does not
provide high-speed directional
elements and high-speed distance
elements.
High-Speed Tripping. The SEL-421 uses the HSDPS (High-Speed Directional
and Phase Selection) element and high-speed distance elements for subcycle
detection of power system faults.
Reclosing. Incorporate programmable single-pole and three-pole tripping and
reclosing of one and two circuit breakers into an integrated substation con-
trol system. Synchronism and voltage checks from multiple sources provide
complete bay control.
Breaker Failure. The SEL-421 incorporates CT subsidence detection to pro-
duce element dropout in 5/8 cycle. Apply the SEL-421 to supply three-pole
breaker failure for one or two breakers. Included is the necessary logic for
single-pole and three-pole breaker failure retrip and initiation of transfer trip-
ping.
Figure 1.1 SEL-421 Functional Overview
➤ Password Separation of Protection and Automation
➤ Expanded SELOGIC Control Equations
➤ Event Reports and Oscillography
➤ Sequential Events Recorder
➤ Dual Breaker Condition Monitor
➤ Station Battery Monitor
➤ DNP3
➤ IEC 61850 (Optional Feature)
➤ High-Accuracy Metering
➤ MIRRORED BITS Communications
➤ Synchrophasors
➤ Fault Locator
➤ CCVT Transient Overreach and Load Encroach-
ment Supervision
➤ Remote and Local Control Switches
➤ Advanced Local Display
➤ Time-Domain Link Remote Data Acquisition
SEL-2600
Bus
3
Line
Bus
3
3
1
SEL-2800
1
ENV
21
25
50BF
5150
50BF
5150
67 68
79
81
O
U
SEL-421
27 59
4
EIA -232
2
Ethernet
1
*
1
IRIG-B
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