ABB REC650 Commissioning Manual page 115

1MRK 511 248-UEN -
Commissioning Manual
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 Three times zero-sequence current. Often referred to as the
O
residual or the earth-fault current
3U Three times the zero sequence voltage. Often referred to as
O
the residual voltage or the neutral point voltage
Section 9
Glossary
107