Schweitzer Engineering Laboratories SEL-421-4, Instruction Manual

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GL.25
Date Code 20171006 Instruction Manual SEL-400 Series Relays
Glossary
Virtual Terminal Connection — Zone Time Delay
Virtual
Terminal Connection
A mechanism that uses a virtual serial port to provide the equivalent functions of
a dedicated serial port and a terminal.
Volatile Storage A storage device that cannot retain data following removal of relay power.
Voltage Compensation Adjustment of the voltage signals to nullify any standing unbalance voltage.
VT Voltage transformer. Also referred to as a potential transformer or PT.
Warm Start The reset of a running system without removing and restoring power.
Weak Infeed Logic Logic that permits rapid tripping for internal faults when a line terminal has
insufficient fault current to operate protective elements.
Winding Transformer winding, synonymous with “terminal.”
Wye A phase-to-neutral connection of circuit elements, particularly voltage
transformers or loads. To form a wye connection using transformers, connect the
nonpolarity side of each of three voltage transformer secondaries in common (the
neutral), and take phase to neutral voltages from each of the remaining three
leads. When properly phased, these leads represent the A-Phase-, B-Phase-, and
C-Phase-to-neutral voltages. This connection is frequently called ‘four-wire
wye,’ alluding to the three phase leads plus the neutral lead.
XML Extensible Markup Language. This specification developed by the W3C (World
Wide Web Consortium) is a pared-down version of SGML designed especially
for web documents. It allows designers to create their own customized tags,
enabling the definition, transmission, validation, and interpretation of data among
applications and organizations.
Zero-Sequence A configuration of three-phase currents and voltages with currents and voltages
that occur simultaneously, are always in phase, and have equal magnitude
(3I
0
= I
A
+ I
B
+ I
C
).
Zero-Sequence
Compensation Factor
A factor based on the zero-sequence and positive-sequence impedance of a line
that modifies a ground-distance element to have the same reach as a phase-
distance element.
Zero-Sequence Impedance Impedance of a device or circuit resulting in current flow when a single voltage
source is applied to all phases.
Zero-Sequence
Mutual Coupling
Zero-sequence current in an unbalanced circuit in close proximity to a second
circuit induces voltage into the second circuit. When not controlled by protection
system design and relay settings, this situation can cause improper operation of
relays in both systems.
Zero-Sequence
Overcurrent Element
Overcurrent protection that operates at conditions exceeding a threshold of
system unbalance.
Zero-Sequence
Voltage-Polarized
Directional Element
An element that provides directionality by the sign, plus or minus, of the
measured zero-sequence impedance.
Z-Number That portion of the relay FID string that identifies the proper
AC
SEL
ERATOR
QuickSet software relay driver version and HMI driver version when creating or
editing relay settings files.
Zone Time Delay Time delay associated with the forward or reverse step distance and zone protection.