Figure 2.1: Three Zones of Phase and Ground Mho Distance Protection
Residual Overcurrent Backup Protection for Ground Faults
Time-overcurrent element detects highly resistive ground faults.
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Four curve families (moderate, inverse, very inverse, and extremely inverse).
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Nondirectional or forward-reaching, as enabled in relay settings.
Instantaneous residual overcurrent element.
-
Nondirectional or forward-reaching, as enabled.
Negative-sequence directional polarization.
Negative-Sequence Directional Element
Directional polarization is based upon negative-sequence voltage and current.
Adds security to phase and ground distance elements.
May polarize ground directional overcurrent protection, if enabled.
Loss-of-Potential (LOP) Detection
Detects blown secondary potential fuse(s) condition.
Enabled or disabled with a simple setting.
When enabled, an LOP condition blocks all mho distance elements.
LOP detection may be selected to close programmable output relay or the ALARM
contact for indication purposes.
Nondirectional Phase Overcurrent Elements
Low-set phase overcurrent elements supervise phase distance elements and release the
TRIP output contacts in conjunction with the low-set residual overcurrent element.
Low-set phase overcurrent elements help detect blown potential fuses in Loss-of-Potential
logic.
Date Code 920508
Specifications
SEL-221F, -1 Instruction Manual
2-3
Summary of Contents for SEL-221F
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Page 158: ...SETTINGS SHEET FOR SEL 221F RELAY PAGE 2 OF 6 DATE Date Code 921110 ...
Page 160: ...SETTINGS SHEET PAGE 4 OF 6 FOR SEL 221F RELAY DATE Date Code 930601 ...
Page 161: ...SETTINGS SHEET PAGE 5 OF 6 FOR SEL 221F RELAY DATE Date Code 961208 ...
Page 229: ...SEL 200 Series Relay Main Board Troubleshooting Test Points and Jumper Locations ...