Time/Current Characteristics - ABB REJ 523 Technical Reference Manual

REJ 523
4.1.3.2
14
Technical Reference Manual
chosen, six time/current curve groups are available. Four of the groups comply with
the standards BS 142 and IEC 60255, and are called "normal inverse ", "very
inverse", "extremely inverse" and "long-time inverse". The two additional inverse-
time curve groups are called "RI-" and "RD-curves".
The inverse-time function of stage I> can be inhibited when stage I>> is started. In
this case the operate time is determined by stage I>>.
If not needed, the stage I>> can be set out of operation completely. This state is
indicated by three dashes "---" on the LCD and by "999" when the set start current
value is read via serial communication.
The set start current value I>>/I
situation, i.e. when the object to be protected is connected to a network. Thus a set
start current value below the connection inrush current level may be selected for the
overcurrent stage I>>. A start situation is defined as a situation where the phase
current rises from a value below 0.12 x I> to a value above 1.5 x I> in less than 60 ms.
The start situation ends when the current falls below 1.25 x I>.

Time/current characteristics

The overcurrent stage I> can be given a definite-time or an inverse definite minimum
time operation characteristic. The settings of switches SGF3/1...6 determine the
operation mode of the stage. Refer to section "Settings". At the IDMT characteristic,
the operate time of the stage is a function of the current: the higher the current, the
shorter the operate time. Six time/current curve groups are available. Four of these
comply with the standards BS 142 and IEC 60255 and two curve groups, RI and RD,
are special type curve groups according to ABB praxis.
Characteristics according to IEC 60255 and BS 142
The relay module incorporates four internationally standardized time/current curve
groups called "extremely inverse", "very inverse", "normal inverse" and "long-time
inverse". The relationship between time and current is in accordance with the
standards BS 142 and IEC 60255-4, and can be expressed as follows:
of stage I>> can be automatically doubled in a start
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