Unix. TCP/IP was developed by DARPA for Internet working
and encompasses both network layer and transport layer
protocols. While TCP and IP specify two protocols at specific
protocol layers, TCP/IP is often used to refer to the entire US
Department of Defense protocol suite based upon these,
including Telnet, FTP, UDP and RDP.
TNC connector
Threaded Neill-Concelman, a threaded constant impedance
version of a BNC connector
TPZ, TPY, TPX,
TPS
Current transformer class according to IEC
UMT
User management tool
Underreach
A term used to describe how the relay behaves during a fault
condition. For example, a distance relay is underreaching when
the impedance presented to it is greater than the apparent
impedance to the fault applied to the balance point, that is, the
set reach. The relay does not “see” the fault but perhaps it
should have seen it. See also Overreach.
U/I-PISA
Process interface components that deliver measured voltage and
current values
UTC
Coordinated Universal Time. A coordinated time scale,
maintained by the Bureau International des Poids et Mesures
(BIPM), which forms the basis of a coordinated dissemination
of standard frequencies and time signals. UTC is derived from
International Atomic Time (TAI) by the addition of a whole
number of "leap seconds" to synchronize it with Universal Time
1 (UT1), thus allowing for the eccentricity of the Earth's orbit,
the rotational axis tilt (23.5 degrees), but still showing the
Earth's irregular rotation, on which UT1 is based. The
Coordinated Universal Time is expressed using a 24-hour clock,
and uses the Gregorian calendar. It is used for aeroplane and
ship navigation, where it is also sometimes known by the
military name, "Zulu time." "Zulu" in the phonetic alphabet
stands for "Z", which stands for longitude zero.
UV
Undervoltage
WEI
Weak end infeed logic
VT
Voltage transformer
X.21
A digital signalling interface primarily used for telecom
equipment
3I
O
Three times zero-sequence current. Often referred to as the
residual or the -fault current
1MRK 511 245-UUS -
Section 10
Glossary
650 series ANSI
121
Engineering Manual
