Hitachi 650 Series Operation Manual page 83

Hide thumbs Also See for 650 Series:

Table of Contents

1MRK500128-UEN Rev. H

UMT

Underreach

UTC

WEI

650 series

Operation 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

Section 9

Glossary

Table of Contents