GL.6
SEL-421/SEL-421-1 Relay
Date Code 20020501
Glossary
Current Reversal Guard Logic
—
Delta
Current
Reversal Guard Logic
Under this logic, the relay does not key the transmitter and ignores reception
of a permissive signal from the remote terminal when a reverse-looking
element detects an external fault.
Current
Transformer Saturation
The point of maximum current input to a current transformer; any change of
input beyond the saturation point fails to produce any appreciable change in
output.
CVT
Capacitive voltage transformer that uses a capacitive voltage divider to reduce
transmission voltage to a level safe for metering and relaying devices. See
CCVT.
CVT Transient Blocking
Logic that prevents transient errors on capacitive voltage transformers from
causing false operation of Zone 1 mho elements.
CVT Transient
Detection Logic
Logic that detects transient errors on capacitive voltage transformers.
Data Bit
A single unit of information that can assume a value of either logical 0 or
logical 1 and can convey control, address, information, or frame check
sequence data.
Data Label
The identifier for a particular data item.
Data Objects
Individual pieces of UCA data created from instances of common class
components or data items that are instances of standard data types.
DC Offset
A dc component of fault current that results from the physical phenomenon
preventing an instantaneous change of current in an inductive circuit.
DCB (Directional
Comparison Blocking)
A communications-assisted protection scheme. A fault occurring behind a
sending relay causes the sending relay to transmit a blocking signal to a
remote relay; the blocking signal interrupts the tripping circuit of the remote
relay and prevents tripping of the protected line.
DCE Devices
Data communication equipment devices (modems).
DCUB (Directional
Comparison Unblocking)
A communications-assisted tripping scheme with logic added to a POTT
scheme that allows high-speed tripping of overreaching elements for a brief
time during a loss of channel. The logic then blocks trip permission until the
communications channel guard returns for a set time.
Deadband
The range of variation an analog quantity can traverse before causing a
response.
Deassert
To deactivate. To remove the logic or electrical requirements needed to
operate a device. To clear a logic condition to its false state (logical 0). To
open the circuit or open the contacts across an SEL-421 Relay input. To open
a normally open output contact. To close a normally closed output contact.
Debounce Time
The time that masks the period when relay contacts continue to move after
closing; debounce time covers this indeterminate state.
Default Data Map
The default map of objects and indices that the SEL-421 Relay uses in DNP
protocol.
Delta
A phase-to-phase series connection of circuit elements, particularly voltage
transformers or loads.
Содержание SEL-421
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