GL.16
SEL-400 Series Relays Instruction Manual Date Code 20171006
Glossary
Motor Running Time—NOT Operator
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.
MVA
Mega Volt-Ampere. Typical unit for expressing the capacity of a power
transformer, e.g., 100MVA.
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.
Nonvolatile Memory
Relay memory that persists over time to maintain the contained data even when
the relay is de-energized.
NOT Operator
A logical operator that produces the inverse value.
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