GL.12
SEL-421/SEL-421-1 Relay
Date Code 20020501
Glossary
Loss of Channel
—
Negative-Sequence
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.
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 SEL
OGIC
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 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.
Mho Characteristic
A directional distance relay characteristic that plots a circle for the basic relay
operation characteristic on an R-X diagram.
M
IRRORED
B
ITS™
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.
Motor Running Time
The circuit breaker motor running time. Depending on your particular circuit
breaker, you can use the motor running time to monitor the charge time of the
circuit breaker springs or the running time of the compressor motor.
MOV
Metal-oxide varistor.
Negation Operator
A SEL
OGIC
control equation math operator that changes the sign of the
argument. The argument of the negation operation is multiplied by –1.
Negative-Sequence
A configuration of three-phase currents and voltages. The currents and
voltages have equal magnitude and a phase displacement of 120°, and have
clockwise phase rotation with current and voltage maxima that occur
Summary of Contents for SEL-421
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