Hitachi REC670, Commissioning Manual

Page: 239 / 242

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
earth-fault current
3U
O
Three times the zero sequence voltage. Often referred to as the residual
voltage or the neutral point voltage
1MRK 511 403-UEN Rev. L Section 15
Glossary
Bay control REC670 233
Commissioning manual
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