GL.7
Date Code 20020903 SEL-587Z Relay
Glossary
Negative-Sequence—Pickup Time
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
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.
NEMA
National Electrical Manufacturers’ Association.
Neutral Impedance
An impedance from neutral to ground on a device such as a generator or
transformer.
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. Represented by the !
symbol.
Optoisolated Input
Relay inputs for monitoring the state of external circuits. Connect auxiliary
relay and circuit breaker contacts to the optoisolated inputs.
OR Operator
Logical OR. A Boolean SELOGIC 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.
Represented by the + symbol.
Parentheses Operator
Use paired parentheses to control the execution of operations in a SELOGIC
control equation.
PC
Personal computer.
Peak Demand Metering
Maximum demand and a time stamp for phase currents, negative-sequence
and zero-sequence currents, and powers. The SEL-587Z Relay stores peak
demand values and the date and time these occurred to nonvolatile storage
once per day, overwriting the previously stored value if the new value is larger.
Should the relay lose control power, the relay restores the peak demand
information saved at 23:50 hours on the previous day.
Phase Overcurrent
Element
Elements that operate by comparing the phase current applied to the
secondary current inputs with the phase overcurrent setting. The relay asserts
these elements when any combination of the phase currents exceeds phase
current setting thresholds.
Phase Rotation
The sequence of voltage or current phasors in a multiphase electrical system.
In an ABC phase rotation system, the B-phase voltage lags the A-phase
voltage by 120°, and the C-phase voltage lags B-phase voltage by 120°. In an
ACB phase rotation system, the C-phase voltage lags the A-phase voltage by
120°, and the B-phase voltage lags the C-phase voltage by 120°.
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
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