Schweitzer Engineering Laboratories SEL-421-4 - Page 1501

GL.9
Date Code 20171006 Instruction Manual SEL-400 Series Relays
Glossary
Distance Calculation Smoothness—EIA-232
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.
Dynamic Zone Selection
The process by which the currents from the CTs are assigned to or removed from
the differential calculations as a function of the Boolean value (logical 0 or
logical 1) of a particular SEL
OGIC equation.
ECB
(EtherCAT
Communications Board)
A circuit board mounted within the relay that has eight EtherCAT fiber
connections for creating a TiDL system.
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.