U.1.2
SEL-421 Relay
User’s Guide
Date Code 20090715
Introduction and Specifications
Features
Features
The SEL-421 contains many protection, automation, and control features.
presents a simplified functional overview of the relay.
Figure 1.1
SEL-421 Functional Overview
SEL-421 features include the following:
Superior Protection.
Combine five zones of phase distance and ground
distance 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 Element™ optimizes directional element
performance and eliminates many settings. Additional logic prevents
Zone 1 overreach on series-compensated lines.
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 control system. Synchronism and voltage checks from
multiple sources provide complete bay control.
Breaker Failure.
The SEL-421 incorporates CT subsidence detection to
produce 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 tripping.
Bus
Bus
Line
SEL-421 Relay
21
50BF
68
67
50
51
79
25
3
1
3
1
3
Phase &
Ground
Distance
Directional
Overcurrent
Out-of-Step
Trip and / or
Block
Dual Circuit
Breaker Failure
49
Thermal
Element
Synchronism
Check
Single- /
Three-Pole
Reclosing
Time-
Overcurrent
Instantaneous
Overcurrent
52
52
* Optional Features
SEL-2600
• Password Separation of
Protection and Automation
• Expanded
SEL
OGIC
®
Control
Equations
• Event Reports and Oscillography
• Sequential Events Recorder
• Dual
Breaker
Condition
Monitor
• Station
Battery
Monitor
• DNP3 Serial, Ethernet, and/or
IEC 61850 Protocol*
• High-Accuracy
Metering
• M
IRRORED
B
ITS
®
Communications
• Synchrophasors
• Fault
Locator
• CCVT Transient Overreach and
Load Encroachment Supervision
• Remote
and
Local
Control
Switches
• Advanced
Local
Display
NOTE:
The SEL-421-1 and the
SEL-421-2 do not provide series-
compensated line protection logic.
NOTE:
The SEL-421-1 and the
SEL-421-2 do not provide high-speed
directional elements and high-speed
distance elements.
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