GL.2
SEL-751A Relay Instruction Manual Date Code 20100129
Glossary
Arc-Flash Hazard—Delta
Arc-Flash Hazard
A dangerous condition associated with the release of energy cause by an elec-
tric arc.
ASCII
Abbreviation for American Standard Code for Information Interchange.
Defines a standard way to communicate text characters between two elec-
tronic devices. The SEL-751A Feeder Protection Relay uses ASCII text char-
acters to communicate using the relay front- and rear-panel EIA-232 serial
ports.
Assert
To activate; to fulfill the logic or electrical requirements needed to operate a
device. To apply a short-circuit or closed contact to an SEL-751A input. To set
a logic condition to the true state (logical 1). To close a normally-open output
contact. To open a normally-closed output contact.
Breaker
Auxiliary Contact
A spare electrical contact associated with a circuit breaker that opens or closes
to indicate the breaker position. A form-a breaker auxiliary contact (ANSI
Standard Device Number 52A) closes when the breaker is closed, opens when
the breaker is open. A form-b breaker auxiliary contact (ANSI Standard
Device Number 52B) opens when the breaker is closed and closes when the
breaker is open.
Checksum
A numeric identifier of the firmware in the relay. Calculated by the result of a
mathematic sum of the relay code.
CID
Abbreviation for Checksum Identifier. The checksum of the specific firmware
installed in the relay.
Contiguous
Items in sequence; the second immediately following the first.
CR_RAM
Abbreviation for Critical RAM. Refers to the area of relay Random Access
Memory (RAM) where the relay stores mission-critical data.
CRC-16
Abbreviation for Cyclical Redundancy Check-16. A mathematical algorithm
applied to a block of digital information to produce a unique, identifying num-
ber. Used to ensure that the information was received without data corruption.
CT
Abbreviation for current transformer.
Current
Unbalance
The SEL-751A calculates the magnitudes of the measured phase currents, cal-
culates the average of those magnitudes, determines the magnitude with the
largest deviation from average. It then calculates the difference between the
magnitude average and magnitude of the phase with the largest deviation from
the average. Finally, the relay calculates the percent unbalance current by
dividing the difference value by the CT nominal current or by the average
magnitude, whichever is larger.
Deassert
To deactivate; to remove the logic or electrical requirements needed to operate
a device. To remove a short-circuit or closed contact from an SEL-751A input.
To clear a logic condition to the false state (logical 0). To open a normally-
open output contact. To close a normally-closed output contact.
Delta
A phase-to-phase connection of voltage transformers for electrical measuring
purposes. Typically, two voltage transformers are used with one primary lead
of the first transformer connected to A-phase and the other lead connected to
B-phase. The second voltage transformer is connected to measure the voltage
from B-phase to C-phase. When two transformers are used, this connection is
frequently called “Open-Delta.”
To Next Page
Loading...
