GL.13
Date Code 20020501
SEL-421/SEL-421-1 Relay
Glossary
Negative-Sequence Current Supervision Pickup
—
Override Values
differently from that for positive-sequence configuration. If positive-sequence
maxima occur as ABC, negative-sequence maxima occur as ACB.
Negative-Sequence
Current Supervision
Pickup
An element allowed to operate only when a negative-sequence current
exceeds a threshold.
Negative-Sequence
Directional Element
An element that provides directivity by the sign, plus or minus, of the
measured negative-sequence impedance.
Negative-Sequence
Impedance
Impedance of a device or circuit that results in current flow with a balanced
negative-sequence set of voltage sources.
Negative-Sequence
Overcurrent Elements
Elements that operate by comparing a negative-sequence calculation of the
three-phase secondary inputs with negative-sequence overcurrent setting
thresholds. The relay asserts these elements when a relay negative-sequence
calculation exceeds negative-sequence current setting thresholds.
Negative-Sequence
Voltage-Polarized
Directional Element
These directional elements are 32QG and 32Q. 32QG supervises the ground
distance elements and residual directional overcurrent elements; 32Q
supervises the phase distance elements.
NEMA
National Electrical Manufacturers’ Association.
Neutral Impedance
An impedance from neutral to ground on a device such as a generator or
transformer.
No Current/Residual
Current Circuit Breaker
Failure Protection Logic
Logic for detecting and initiating circuit breaker failure protection with a logic
transition, or when a weak source drives the fault or a high-resistance ground
fault occurs.
Nondirectional Start
A blocking signal provided by nondirectional overcurrent elements to a
remote terminal used in DCB communications-assisted tripping schemes. The
nondirectional start elements start sending the block signal.
Nonhomogeneous System
A power system with a large angle difference (>5° difference) for the
impedance angles of the local source, the protected line, and the remote
source.
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.
Summary of Contents for SEL-421
Page 8: ...This page intentionally left blank ...
Page 30: ...This page intentionally left blank ...
Page 110: ...This page intentionally left blank ...
Page 204: ...This page intentionally left blank ...
Page 284: ...This page intentionally left blank ...