GL.15
Date Code 20171006 Instruction Manual SEL-400 Series Relays
Glossary
Logical Node—Model
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 relay 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.
Merging Unit
A device that converts analog signals to digital signals and transmits them as
IEC 61850-9-2 data.
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.
MMS
Manufacturing messaging specification, a data exchange protocol used by UCA.
MOD
Motor-operated disconnect.
Model
Model of device (or component of a device) including the data, control access,
and other features in UCA protocol.
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