GL.16
SEL-421 Relay Date Code 20090715
Glossary
Pole Discrepancy—Qualifier Code
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 current transformer
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 SEL-421 relays had a TIME
1k PPS input.
Protection and
Automation Separation
Segregation of protection and automation processing and settings.
Protection Settings Group
Individual scheme settings for as many as six different schemes (or instances).
Protection-Disabled State
Suspension of relay protection element and trip/close logic processing and
deenergization of all control outputs.
PT
Potential transformer. Also referred to as a voltage transformer or VT.
PTR
Potential transformer ratio.
Quadrilateral
Characteristic
A distance relay characteristic on an R-X diagram consisting of a directional
measurement, reactance measurement, and two resistive measurements.
Qualifier Code
Specifies type of range for DNP3 objects. With the help of qualifier codes,
DNP master devices can compose the shortest, most concise messages.
Courtesy of NationalSwitchgear.com
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