GL.7
Date Code 20170927 Instruction Manual SEL-751 Relay
Glossary
RMS—VS
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-751 (and the SEL-2600 RTD Module) can measure the resistance of
the RTD, and thus determine the temperature at the RTD location. Typically
embedded in the motor windings or attached to the races of bearings.
Self-Test
A function that verifies the correct operation of a critical device subsystem
and indicates if the relay has detected an out-of-tolerance condition. The
SEL-751 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 1024 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.
Terminal
Emulation Software
Personal computer (PC) software that you can use to send and receive ASCII
text messages via the PC serial port.
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).
Underfrequency Element
A protection element that causes the relay to trip when the measured electrical
system frequency is less than a settable frequency.
VA, VB, VC
Measured A-, B-, and C-phase-to-neutral voltages.
VAB, VBC, VCA
Measured or calculated phase-to-phase voltages.
VG
Residual voltage calculated from the sum of the three phase-to-neutral
voltages, if connected.
VS
Measured phase-to-neutral or phase-to-phase synchronism-check voltage.
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