GL.15
Date Code 20090715
SEL-421 Relay
Glossary
Nonvolatile Memory
—
Polarizing Memory
Nonvolatile Memory
Relay memory that persists over time to maintain the contained data even
when the relay is deenergized.
NOT Operator
A logical operator that produces the inverse value.
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.
Override Values
Test values you enter in Fast Meter, DNP, 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 SEL-421 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°.
Phase Selection
Ability of the relay to determine the faulted phase or phases.
Pickup Time
The time measured from the application of an input signal until the output
signal asserts. You can set the time, as in the case of a logic variable timer, or
the pickup time can be a result of the characteristics of an element algorithm,
as in the case of an overcurrent element pickup time.
Pinout
The definition or assignment of each electrical connection at an interface.
Typically refers to a cable, connector, or jumper.
Polarizing Memory
A circuit that provides a polarizing source for a period after the polarizing
quantity has changed or gone to zero.
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