GL.5
Date Code 20170927 Instruction Manual SEL-751 Relay
Glossary
IN—Overfrequency Element
IN
Neutral current measured by the relay IN input. The IN input is typically
connected to the secondary winding of a window-CT for ground fault
detection on resistance-grounded systems.
IP Address
An identifier for a computer or device on a TCP/IP network. Networks using
the TCP/IP protocol route messages based on the IP address of the destination.
The format of an IP address is a 32-bit numeric address written as four
numbers separated by periods. Each number can be zero to 255. For example,
1.160.10.240 could be an IP address.
IRIG-B
A time code input that the relay can use to set the internal relay clock.
LCD
Abbreviation for Liquid Crystal Display. Used as the relay front-panel
alphanumeric display.
LED
Abbreviation for Light-Emitting Diode. Used as indicator lamps on the relay
front panel.
LEA Inputs
Low-energy analog inputs. LEA voltage inputs are suitable for C37.92
compliant high-impedance sensors, such as capacitive voltage dividers and
resistive voltage dividers.
Logical Node
In IEC 61850, the smallest part of a function that exchanges data. A logical
node (LN) is an object defined by its data and methods. Each logical node
represents a group of data (controls, status, measurements, etc.) associated
with a particular function.
Load Encroachment
The load-encroachment feature allows setting of phase overcurrent elements
independent of load levels.
Loss-of-Potential
Loss of one or more phase voltage inputs to the relay.
MAC Address
The Media Access Control (hardware) address of a device connected to a
shared network medium, most often used with Ethernet networks.
MMS
Manufacturing Messaging Specification, a data exchange protocol used by
IEC 61850.
MIRRORED BITS
Protocol for direct relay-to-relay communications.
NEMA
Abbreviation for National Electrical Manufacturers Association.
Neutral
Overcurrent Element
A protection element that causes the relay to trip when the neutral current
magnitude (measured by the IN input) exceeds a user-settable value. Used to
detect and trip in response to ground faults.
Nominal Frequency
Normal electrical system frequency, usually 50 or 60 Hz.
Nonfail-Safe
Refers to an output contact that is not energized during normal relay
operation. When referred to a trip output contact, the protected equipment
remains in operation unprotected when relay power is removed or if the relay
fails.
Nonvolatile Memory
Relay memory that is able to correctly maintain data it is storing even when
the relay is de-energized.
Overfrequency Element
A protection element that causes the relay to trip when the measured electrical
system frequency exceeds a settable frequency.
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