ABB REG650 Technical Manual page 725

Generator protection

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1MRK 502 048-UEN A

Technical manual

User management tool

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.

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.

Undervoltage

Weak end infeed logic

Voltage transformer

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