GL.5
Date Code 20081022 Instruction Manual SEL-787 Relay
Glossary
Remote Bit–Synchrophasors
asserted contact input or contact output. Logical 0 represents a false logic
condition, dropped out element, or deasserted contact input or contact output.
You can use Relay Word bits in SEL
OGIC control equations to control relay
tripping, event triggering, and output contacts, as well as other functions.
Remote Bit
A Relay Word bit for which state is controlled by serial port commands,
including the CONTROL command, binary Fast Operate command, or
Modbus
®
command.
Residual Current
The sum of the measured phase currents. In normal, balanced operation, this
current is very small or zero. When a ground fault occurs, this current can be
large.
Restricted Earth Fault
Element (REF)
Provides sensitive protection against ground faults in wye-connected
transformer windings. The element is “restricted” to ground faults within a
zone defined by neutral and line CT placement.
RMS
Abbreviation for Root-Mean-Square. Refers to the effective value of the
sinusoidal current and voltage measured by the relay, accounting for the
fundamental frequency and higher order harmonics in the signal.
ROM
Abbreviation for Read-Only Memory. Nonvolatile memory where the relay
firmware is stored.
RTD
Abbreviation for Resistance Temperature Device. An RTD is made of a metal
having a precisely known resistance and temperature coefficient of resistance.
The SEL-787 (and the SEL-2600 series RTD modules) can measure the
resistance of the RTD, and thus, determine the temperature at the RTD
location, typically embedded in the transformer and oil tank.
Transducer
Device that converts the input to the device to an analog output quantity of
either current (±1, 2.5, 5, 10 and 20 mA, or 4–20 ma), or voltage (±1, 2.5, 5, or
10 V).
Self-Test
A function that verifies the correct operation of a critical device subsystem
and indicates if an out-of-tolerance condition is detected. The SEL-787 is
equipped with self-tests that validate the relay power supply, microprocessor,
memory, and other critical systems.
SELOGIC
®
Control Equation
A relay setting that allows you to control a relay function (such as an output
contact) by using a logical combination of relay element outputs and fixed
logic outputs. Logical AND, OR, INVERT, rising edge [/], and falling edge [\]
operators, plus a single level of parentheses are available to use in each control
equation setting.
Sequential
Events Recorder
A relay function that stores a record of the date and time of each assertion and
deassertion of every Relay Word bit in a settable list. Provides a useful way to
determine the order and timing of events following a relay operation.
SER
Abbreviation for Sequential Events Recorder or the relay serial port command
to request a report of the latest 512 sequential events.
Synchrophasors
The word synchrophasor is derived from two words: synchronized phasor.
Synchrophasor measurement refers to the concept of providing measurements
taken on a synchronized schedule in multiple locations. A high-accuracy
clock, commonly a Global Positioning System (GPS) receiver such as the
SEL-2407 Satellite-Synchronized Clock, makes synchrophasor measurement
possible.
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