GL.7
Date Code 20090715 SEL-421 Relay
Glossary
Data Bit—Directional Supervision
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 Class
In the IEC 61850 protocol, an aggregation of classes or data attributes.
Data Label
The identifier for a particular data item.
Data Object
In the IEC 61850 protocol, part of a logical node representing specific
information (status or measurement, for example). From an object-oriented
point of view, a data object is an instance of a data class.
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 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 uses in DNP
protocol.
Delta
A phase-to-phase series connection of circuit elements, particularly voltage
transformers or loads.
Demand Meter
A measuring function that calculates a rolling average or thermal average of
instantaneous measurements over time.
Direct Tripping
Local or remote protection elements provide tripping without any additional
supervision.
Directional Start
A blocking signal provided by reverse reaching elements to a remote terminal
used in DCB communications-assisted tripping schemes. If the fault is internal
(on the protected line), the directional start elements do not see the fault and
do not send a blocking signal. If the fault is external (not on the protected
line), the directional start elements start sending the block signal.
Directional Supervision
The relay uses directional elements to determine whether protective elements
operate based on the direction of a fault relative to the relay.
Courtesy of NationalSwitchgear.com
To Next Page
Loading...
