GL.8
SEL-421 Relay Date Code 20090715
Glossary
Disabling Time Delay—Electrical Operating Time
Disabling Time Delay
A DCUB scheme timer (UBDURD) that prevents high-speed tripping
following a loss-of-channel condition.
Distance
Calculation Smoothness
A relay algorithm that determines whether the distance-to-fault calculation
varies significantly or is constant.
Distance Protection Zone
The area of a power system where a fault or other application-specific
abnormal condition should cause operation of a protective relay.
DMTC Period
The time of the demand meter time constant in demand metering.
DNP (Distributed
Network Protocol)
Manufacturer-developed, hardware-independent communications protocol.
Dropout Time
The time measured from the removal of an input signal until the output signal
deasserts. You can set the time, in the case of a logic variable timer, or the
dropout time can be a result of the characteristics of an element algorithm, as
in the case of an overcurrent element dropout time.
DTE Devices
Data terminal equipment (computers, terminals, printers, relays, etc.).
DTT (Direct Transfer
Trip)
A communications-assisted tripping scheme. A relay at one end of a line
sends a tripping signal to the relay at the opposite end of the line.
Dumb Terminal
See ASCII terminal.
DUTT
(Direct Underreaching
Transfer Trip)
A communications-assisted tripping scheme. Detection of a Zone 1 fault at
either end of a line causes tripping of the local circuit breaker as well as
simultaneous transmission of a tripping signal to the relay at the opposite end
of the line. The scheme is said to be underreaching because the Zone 1 relays
at both ends of the line reach only 80 percent (typically) of the entire line
length.
Echo
The action of a local relay returning (echoing) the remote terminal permissive
signal to the remote terminal when the local breaker is open or a weak infeed
condition exists.
Echo Block Time Delay
A time delay that blocks the echo logic after dropout of local permissive
elements.
Echo Duration Time Delay
A time delay that limits the duration of the echoed permissive signal.
ECTT
(Echo Conversion to Trip)
An element that allows a weak terminal, after satisfaction of specific
conditions, to trip by converting an echoed permissive signal to a trip signal.
EEPROM
Electrically Erasable Programmable Read-Only Memory. Nonvolatile
memory where relay settings, event reports, SER records, and other
nonvolatile data are stored.
EHV
Extra high voltage. Voltages greater than 230 kV.
EIA-232
Electrical definition for point-to-point serial data communications interfaces,
based on the standard EIA/TIA-232. Formerly known as RS-232.
EIA-485
Electrical standard for multidrop serial data communications interfaces, based
on the standard EIA/TIA-485. Formerly known as RS-485.
Electrical Operating Time
Time between trip or close initiation and an open phase status change.
Courtesy of NationalSwitchgear.com
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