ABB REL670 2.2 IEC, Applications Manual

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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 506 369-UEN B
Section 26
Glossary
Line distance protection REL670 2.2 IEC 899
Application manual