TYP Type identification
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.
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 ground-fault current
3V
O
Three times the zero sequence voltage. Often referred to as the
residual voltage or the neutral point voltage
1MRK 504 165-UUS - Section 16
Glossary
Transformer protection RET670 2.2 ANSI 319
Commissioning manual
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