GL.6
SEL-749M Relay Instruction Manual Date Code 20080918
Glossary
Self-Test—Z-Number
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-749M 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.
Speed Switch
An electrical contact that closes to indicate that a motor speed exceeds a cer-
tain value.
Star
Motor winding configuration during Star-Delta starting.
Ter min a l
Emulation Software
Personal computer (PC) software that can be used to send and receive ASCII
text messages via the PC serial port.
Underfrequency Element
A protection element that causes the relay to trip when the measured electrical
system frequency is less than a settable frequency.
Underpower Element
A protection element that causes the relay to trip when the measured electrical
power consumed by a motor is less than a settable value.
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 volt-
ages, if connected.
VT
Abbreviation for voltage transformer. Also referred to as a potential trans-
former or PT.
Wye
As used in this instruction manual, a phase-to-neutral connection of voltage
transformers for electrical measuring purposes. Three voltage transformers are
used with one primary lead of the first transformer connected to A-phase and
the other lead connected to ground. The second and third voltage transformers
are connected to measure the voltage from B-phase and C-phase-to-ground,
respectively. This connection is frequently called ‘four-wire wye,’ alluding to
the three phase leads plus the neutral lead.
Z-Number
That portion of the relay RID string that identifies the proper ACSELERATOR
software relay driver version when creating or editing relay settings files.
Courtesy of NationalSwitchgear.com
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