ABB Relion RES670 Operator's Manual page 92

Section 15
Glossary
86
UV
WEI
VT
X.21
3I
O
3U
O
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.
Undervoltage
Weak end infeed logic
Voltage transformer
A digital signalling interface primarily used for telecom
equipment
Three times zero-sequence current. Often referred to as the
residual or the earth-fault current
Three times the zero sequence voltage. Often referred to as
the residual voltage or the neutral point voltage
1MRK511251-UEN B
Operator's manual