REJ 513
User’s Guide
ABB Substation Automation
Products and Systems
1MRS750613-MUM
18
The low-set stage of the overcurrent unit may be given a definite-time or an inverse
definite minimum time (IDMT) characteristic. When the IDMT characteristic is
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 “999” when the set start current value is read via serial communication.
The set start current value I>>/ I
n
of stage I>> can be automatically doubled in a start
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>.
2.1.3.3
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 mode
of operation. 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:
Summary of Contents for REJ 513
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