ABB Relion 670 Series Technical Reference Manual page 714

Section 20
Inverse time characteristics
708
Operate
time
tMin
IMin
IEC05000133 V2 EN
Figure 346: 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 pickup 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 89:
æ
ç
k
=
t s [ ]
ç
in
ç
- ×
0.339 0.235
è
EQUATION1194 V1 EN
where:
in> is the set start current for step n
k is set time multiplier for step n
i is the measured current
IEC05000133-3-en.vsd
ö
÷
÷
>
÷
ø
i
1MRK 505 208-UEN B
Current
(Equation 89)
Technical reference manual