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GL.17
Date Code 20171006
Instruction Manual
SEL-400 Series Relays
Glossary
Operate Current
—
Phase Rotation
Operate Current
Differential current (vector sum) between current(s) that enter a point, and
current(s) that leave that point.
OR Operator
Logical OR. A Boolean SEL
OGIC
control equation operator that compares two
Boolean values and yields either a logical 1 if either compared Boolean value is
logical 1 or a logical 0 if both compared Boolean values are logical 0.
OSI
Open Systems Interconnect. A model for describing communications protocols.
Also an ISO suite of protocols designed to this model.
Out-of-Step Blocking
Blocks the operation of phase-distance elements during power swings.
Out-of-Step Tripping
Trips the circuit breaker(s) during power swings.
Outboard CT
Current transformer physically positioned in such a way that the CT remains in
circuit when the feeder is on transfer.
Over/Underpower
Elements
Elements that calculate the forward and reverse power flow and compare the
result against settable thresholds.
Over/Undervoltage
Elements
Elements that calculate the system voltage and compare the result against settable
thresholds.
Over/Underfrequency
Elements
Elements that calculate the power system frequency and compare the result
against settable thresholds.
Overlap Configuration
Configuration of the tie-breaker protection whereby the area between the tie-
breaker CTs are part of two bus-zones, i.e., a fault between the tie-breaker CTs is
common to two bus-zones.
Override Values
Test values you enter in Fast Meter, DNP3, and communications card database
storage.
Parentheses Operator
Math operator. Use paired parentheses to control the execution of operations in a
SEL
OGIC
control equation.
PC
Personal computer.
Peak Demand Metering
Maximum demand and a time stamp for phase currents, negative-sequence and
zero-sequence currents, and powers. The relay stores peak demand values and the
date and time these occurred to nonvolatile storage once per day, overwriting the
previously stored value if the new value is larger. Should the relay lose control
power, the relay restores the peak demand information saved at 23:50 hours on
the previous day.
Phase-Distance Element
A mho distance element the relay uses to detect phase-to-phase and three-phase
faults at a set reach along a transmission line.
Phase Overcurrent
Element
Elements that operate by comparing the phase current applied to the secondary
current inputs with the phase overcurrent setting. The relay asserts these elements
when any combination of the phase currents exceeds phase current setting
thresholds.
Phase Rotation
The sequence of voltage or current phasors in a multiphase electrical system. In
an ABC phase rotation system, the B-Phase voltage lags the A-Phase voltage by
120°, and the C-Phase voltage lags B-Phase voltage by 120°. In an ACB phase
rotation system, the C-Phase voltage lags the A-Phase voltage by 120°, and the
B-Phase voltage lags the C-Phase voltage by 120°.
Summary of Contents for SEL-421-4
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