GL.13
Date Code 20090715 SEL-421 Relay
Glossary
Local Bits—M
IRRORED BITS
®
Communications
Local Bits
The Relay Word bit outputs of local control switches that you access through
the SEL-421 front panel. Local control switches replace traditional panel-
mounted control switches.
Lockout Relay
An auxiliary relay that prevents operation of associated devices until it is reset
either electrically or by hand.
Logical 0
A false logic condition, dropped out element, or deasserted control input or
control output.
Logical 1
A true logic condition, picked up element, or asserted control input or control
output.
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.
Loss of Channel
Loss of guard and no permissive signal from communications gear in a DCUB
(directional comparison unblocking scheme) for either two or three terminal
lines.
Loss of Guard
No guard signal from communications gear.
Loss of Potential
Loss of one or more phase voltage inputs to the relay secondary inputs.
Low-Level Test Interface
An interface that provides a means for interrupting the connection between the
relay input transformers and the input processing module and allows inserting
reduced-scale test quantities for relay testing.
MAC Address
The Media Access Control (hardware) address of a device connected to a
shared network medium, most often used with Ethernet networks.
Maintenance Testing
Testing that confirms that the relay is measuring ac quantities accurately and
verifies correct functioning of auxiliary equipment, scheme logic, and
protection elements.
Math Operations
Calculations for automation or extended protection functions.
Math Operators
Operators that you use in the construction of math SELOGIC control equations
to manipulate numerical values and provide a numerical base-10 result.
Maximum Dropout Time
The maximum time interval following a change of input conditions between
the deassertion of the input and the deassertion of the output.
Maximum/Minimum
Meter
Type of meter data presented by the SEL-421 that includes a record of the
maximum and minimum of each value, along with the date and time that each
maximum and minimum occurred.
Mechanical Operating
Time
Time between trip initiation or close initiation and the change in status of an
associated circuit breaker auxiliary 52A normally open contacts.
Mho Characteristic
A directional distance relay characteristic that plots a circle for the basic relay
operation characteristic on an R-X diagram.
MIRRORED BITS
®
Communications
Patented relay-to-relay communications technique that sends internal logic
status, encoded in a digital message, from one relay to the other. Eliminates
the need for some communications hardware.
Courtesy of NationalSwitchgear.com
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