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1-6
Introduction
Date Code 20011026
SEL-321/321-1 Instruction Manual
Applications Highlights
A list of applications and key specifications:
Applications Key
Specifications
Series Compensated Lines
•
Positive-sequence memory polarization
•
Long memory duration for directional stability
Single-Pole Tripping
•
Advanced phase-selection methods
•
Secure protection during open-pole interval
•
Pole-discordance logic trips three-pole for
excessive single-pole-open events
Multiple-Breaker Applications
•
SPT one; 3PT other
•
SPT both; 3PT both
•
Trip coil monitors for up to six poles
•
Stub protection
Long Lines
•
Load-encroachment elements prevent
unwanted trips on load
•
Voltage elements detect local and remote bus
overvoltages
•
Sensitive negative-sequence and residual over-
current elements provide sensitive backup
protection
Tapped and Three-Terminal Lines
•
Four zones
•
Two zero-sequence compensation factors for
more accurate ground-distance reach on either
side of tap
•
Independent reach settings for phase, ground
mho, and ground reactance elements
•
Multiple setting groups cover any switching
configurations
Bus-Tie 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-stepped distance
•
Ground directional overcurrent protection
•
Torque controlled time-overcurrent elements
Lines with Transformers
•
Negative-sequence overcurrent protection
Lines with Reactors
•
Overvoltage elements control reactor insertion
and tripping
Summary of Contents for SEL-321
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