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
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