ABB REF 610 - Page 48

IDMT characteristics according to the IEEE C37.112
REF 610 provides three time/current curve groups which comply with the
IEEE C37.112 standard: extremely inverse, very inverse and inverse. The
relationship between time and current is expressed as follows:
ts
A
I
I
Bn
P
[]
=
>
⎛
⎝
⎜
⎞
⎠
⎟
−
+
⎛
⎝
⎜
⎜
⎜
⎜
⎜
⎞
⎠
⎟
⎟
⎟
⎟
⎟
×
1
(5)
t = operate time
I = phase (or earth-fault) current value
n (or n
0
) = time multiplier
I> (or I
0
>) = set start value
The actual operate time of the relay (see Fig. 5.1.4.9.-5...Fig. 5.1.4.9.-
7), includes an additional filter and detection time, and the operate time
of the trip output contact. When the operate time of the relay is
calculated as above, approximately 30 ms should be added to the
result.
Table 5.1.4.9.-4 Values of constants A, B and P
Time/current curve group A B P
Extremely inverse 6.407 0.025 2.0
Very inverse 2.855 0.0712 2.0
Inverse 0.0086 0.0185 0.02
The time/current curve groups based on the IEEE standard are illustrated in
Fig. 5.1.4.9.-5...Fig. 5.1.4.9.-7.
48
REF 610REF 610
Feeder Protection Relay
Technical Reference Manual
1MRS755310