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
Section 19 1MRK 502 029-UEN A
Glossary
252
Installation and commissioning manual
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