GL.2
SEL-787 Relay Instruction Manual Date Code 20081022
Glossary
Assert–Event History
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-787 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
number. Used to ensure that the information was received without data
corruption.
CT
Abbreviation for current transformer.
Current Differential
Element
A protection element that measures the difference current between the two
windings to detect internal faults.
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-787 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.”
Dropout Time
The time measured from the removal of an input signal until the output signal
deasserts. The time can be settable, as in the case of a logic variable timer, or
can be a result of the characteristics of an element algorithm, as in the case of
an overcurrent element dropout time.
EEPROM
Abbreviation for Electrically Erasable Programmable Read-Only Memory.
Nonvolatile memory where relay settings, event reports, SER records, and
other nonvolatile data are stored.
Event History
A quick look at recent relay activity that includes a standard report header;
event number, date, time, and type; maximum fault phase current; and targets.
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