IEC05000133-3-en.vsd
tMin
Current
Operate
time
IMin
IEC05000133 V2 EN
Figure 319: Minimum time-lag operation for the IEC curves
In order to fully comply with IEC curves definition setting parameter tMin shall be set
to the value which is equal to the operating time of the selected IEC inverse time curve
for measured current of twenty times the set current start value. Note that the operating
time value is dependent on the selected setting value for time multiplier k.
In addition to the ANSI and IEC standardized characteristics, there are also two
additional inverse curves available; the RI curve and the RD curve.
The RI inverse time curve emulates the characteristic of the electromechanical ASEA
relay RI. The curve is described by equation
121:
[ ]
0.339 0.235
=
>
- ×
æ ö
ç ÷
ç ÷
ç ÷
è ø
k
t s
in
i
EQUATION1194 V1 EN
(Equation 121)
where:
in> is the set start current for step n
k is set time multiplier for step n
i is the measured current
Section 21 1MRK 502 048-UEN A
Time inverse characteristics
688
Technical manual
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