1.11
Date Code 20171021
Instruction Manual
SEL-421 Relay
Introduction and Specifications
Applications
Application Highlights
Apply the SEL-421 in power system protection and control situations.
lists applications and key features of the relay.
NOTE:
The SEL-421-4 does not
provide high-speed directional
elements and high-speed distance
elements.
Table 1.1
Application Highlights (Sheet 1 of 2)
Application
Key Features
Single-pole and three-pole
tripping
High-speed distance elements
Best Choice Ground Directional Element
Secure protection during open-pole interval
Pole-discordance logic trips three-pole for excessive single-
pole-open conditions
Remote data acquisition
Time-domain link (TiDL)
Multiple-breaker tripping
SPT one; 3PT other
SPT both; 3PT both
Breaker failure protection
Reclosing and synchronism
check
2 shots SPT; 4 shots 3PT
Leader/follower breaker arrangements
Two-circuit-breaker universal synchronism check
Coupling-Capacitor Voltage
Transformer (CCVT) tran-
sient detection logic
Detect CCVT transients to provide correct operation of the
direct tripping (Zone 1) distance elements
Long lines
Load-encroachment elements prevent unwanted trips on load
Voltage elements detect local bus overvoltages
Sensitive negative-sequence and residual overcurrent ele-
ments provide sensitive backup protection
Tapped and three-
terminal lines
Five zones
Three zero-sequence compensation factors for more accurate
ground-distance reach on either side of tap
Independent reach settings for phase, ground mho and phase,
ground quadrilateral elements
Multiple settings groups cover any switching configurations
Bus-tie or transfer circuit
breakers
Multiple setting groups
Match relay settings group to each line substitution
Eliminate current reversing switches
Local or remote operator switches the setting groups
Subtransmission lines
Time-step distance protection
Ground directional overcurrent protection
Torque-controlled time-overcurrent elements
Lines with capacitors
Series-compensated line logic
Lines with transformers
Negative-sequence overcurrent protection
Short transmission lines
Directional overcurrent elements and communications-
assisted tripping schemes, quadrilateral phase distance
Permissive Overreaching
Transfer Tripping (POTT)
schemes
Current reversal guard logic
Open breaker echo keying logic
Weak-infeed and zero-infeed logic
Time-step distance backup protection
Directional Comparison
Unblocking Tripping
(DCUB) schemes
Includes all POTT logic
All loss-of-channel logic is inside the relay
Time-step distance backup protection
NOTE:
If the relay is using a remote
data acquisition system, such as TiDL,
the operating times will be delayed by
1.5 ms. Use caution when setting the
relay coordination times to account
for this added delay.
NOTE:
The SEL-421-4 does not
provide series-compensated line
protection logic.
Summary of Contents for SEL-421-4
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