GL.14
SEL-421 Relay Date Code 20111215
Glossary
MMS—Nonhomogeneous System
MMS
Manufacturing Messaging Specification, a data exchange protocol used by
UCA.
MOD
Motor-operated disconnect.
Model
Model of device (or component of a device) including the data, control access,
and other features in UCA protocol.
Motor Running Time
The circuit breaker motor running time. Depending on your particular circuit
breaker, you can use the motor running time to monitor the charge time of the
circuit breaker springs or the running time of the compressor motor.
MOV
Metal-oxide varistor.
Negation Operator
A SELOGIC control equation math operator that changes the sign of the
argument. The argument of the negation operation is multiplied by –1.
Negative-Sequence
A configuration of three-phase currents and voltages. The currents and
voltages have equal magnitude and a phase displacement of 120°, and have
clockwise phase rotation with current and voltage maxima that occur
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.
To Next Page
Loading...
