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GL.18
SEL-400 Series Relays
Instruction Manual
Date Code 20171006
Glossary
Phase Selection
—
Process Bus
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.
PMU
Phasor measurement unit. A device that measures and publishes synchrophasor
data.
Polarizing Memory
A circuit that provides a polarizing source for a period after the polarizing
quantity has changed or gone to zero.
Pole Discrepancy
A difference in the open/closed status of circuit breaker poles. The relay
continuously monitors the status of each circuit breaker pole to detect open or
close conditions among the three poles.
Pole-Open Logic
Logic that determines the conditions that the relay uses to indicate an open circuit
breaker pole.
Pole Scatter
Deviation in operating time between pairs of circuit breaker poles.
Port Settings
Communications port settings such as Data Bits, Speed, and Stop Bits.
Positive-Sequence
A configuration of three-phase currents and voltages. The currents and voltages
have equal magnitude and a phase displacement of 120°. With conventional
rotation in the counter-clockwise direction, the positive-sequence current and
voltage maxima occur in ABC order.
Positive-Sequence
Current Restraint
Factor, a2
This factor compensates for highly unbalanced systems with many untransposed
lines and helps prevent misoperation during CT saturation. The a2 factor is the
ratio of the magnitude of negative-sequence current to the magnitude of positive-
sequence current (I2/I1).
Positive-Sequence
Current Supervision
Pickup
An element that operates only when a positive-sequence current exceeds a
threshold.
Positive-Sequence
Impedance
Impedance of a device or circuit that results in current flow with a balanced
positive-sequence set of voltage sources.
POTT (Permissive
Overreaching
Transfer Trip)
A communications-assisted line protection scheme. At least two overreaching
protective relays must receive a permissive signal from the other terminal(s)
before all relays trip and isolate the protected line.
Power Factor
The cosine of the angle by which phase current lags or leads phase voltage in an
ac electrical circuit. Power factor equals 1.0 for power flowing to a pure resistive
load.
PPS
Pulse per second from a GPS receiver. Previous relays had a TIME 1k PPS input.
Primitive Name
The predefined name of a quantity within the relay.
Process Bus
Network bus for IED communication at the bay level.
Summary of Contents for SEL-421-4
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