Appendix D IEC255 Inverse Time Tables
The times shown for the inverse time curves in this appendix are calculated according to the formulas defined in the IEC 255 Standard.
-
Standard Inverse (SI) = 0.14 / (I^0.02-1)
-
Very Inverse (VI) = 13.5 / (I-1)
-
Extremely Inverse (EI) = 80 / (I^2-1)
Where I is the fault current expressed as a multiple of the setting current.
Each curve is defined in terms of a formula such as:
Time = T / (IN – Q) + B
Where:
T = time parameter specific to characteristic
I = ratio of fault current to setting current
N = parameter specific to characteristic
Q = parameter specific to characteristic
B = parameter specific to characteristic
Tables for the calculated times for each of the IEC255 curves are shown in the table below.
Table 104 IEC 255 Inverse Curves Timing Table
|
Setting Current Multiple |
Standard Inverse Time (s) |
Very Inverse Time (s) |
Extremely Inverse Time (s) |
|---|---|---|---|
|
1.10 |
73.37 |
135.00 |
380.95 |
|
1.50 |
17.19 |
27.00 |
64.00 |
|
2.00 |
10.03 |
13.50 |
26.67 |
|
2.50 |
7.57 |
9.00 |
15.24 |
|
3.00 |
6.30 |
6.75 |
10.00 |
|
3.50 |
5.52 |
5.40 |
7.11 |
|
4.00 |
4.98 |
4.50 |
5.33 |
|
4.50 |
4.58 |
3.86 |
4.16 |
|
5.00 |
4.28 |
3.38 |
3.33 |
|
5.50 |
4.04 |
3.00 |
2.74 |
|
6.00 |
3.84 |
2.70 |
2.29 |
|
6.50 |
3.67 |
2.45 |
1.94 |
|
7.00 |
3.53 |
2.25 |
1.67 |
|
7.50 |
3.40 |
2.08 |
1.45 |
|
8.00 |
3.30 |
1.93 |
1.27 |
|
8.50 |
3.20 |
1.80 |
1.12 |
|
9.00 |
3.12 |
1.69 |
1.00 |
|
9.50 |
3.04 |
1.59 |
0.90 |
|
10.00 |
2.97 |
1.50 |
0.81 |
|
10.50 |
2.91 |
1.42 |
0.73 |
|
11.00 |
2.85 |
1.35 |
0.67 |
|
11.50 |
2.80 |
1.29 |
0.61 |
|
12.00 |
2.75 |
1.23 |
0.56 |
|
12.50 |
2.70 |
1.17 |
0.52 |
|
13.00 |
2.66 |
1.13 |
0.48 |
|
13.50 |
2.62 |
1.08 |
0.44 |
|
14.00 |
2.58 |
1.04 |
0.41 |
|
14.50 |
2.55 |
1.00 |
0.38 |
|
15.00 |
2.52 |
0.96 |
0.36 |
|
15.50 |
2.48 |
0.93 |
0.33 |
|
16.00 |
2.46 |
0.90 |
0.31 |
|
16.50 |
2.43 |
0.87 |
0.29 |
|
17.00 |
2.40 |
0.84 |
0.28 |
|
17.50 |
2.38 |
0.82 |
0.26 |
|
18.00 |
2.35 |
0.79 |
0.25 |
|
18.50 |
2.33 |
0.77 |
0.23 |
|
19.00 |
2.31 |
0.75 |
0.22 |
|
19.50 |
2.29 |
0.73 |
0.21 |
|
20.00 |
2.27 |
0.71 |
0.20 |
|
20.50 |
2.25 |
0.69 |
0.19 |
|
21.00 |
2.23 |
0.68 |
0.18 |
|
21.50 |
2.21 |
0.66 |
0.17 |
|
22.00 |
2.20 |
0.64 |
0.17 |
|
22.50 |
2.18 |
0.63 |
0.16 |
|
23.00 |
2.16 |
0.61 |
0.15 |
|
23.50 |
2.15 |
0.60 |
0.15 |
|
24.00 |
2.13 |
0.59 |
0.14 |
|
24.50 |
2.12 |
0.57 |
0.13 |
|
25.00 |
2.11 |
0.56 |
0.13 |
|
25.50 |
2.09 |
0.55 |
0.12 |
|
26.00 |
2.08 |
0.54 |
0.12 |
|
26.50 |
2.07 |
0.53 |
0.11 |
|
27.00 |
2.05 |
0.52 |
0.11 |
|
27.50 |
2.04 |
0.51 |
0.11 |
|
28.00 |
2.03 |
0.50 |
0.10 |
|
28.50 |
2.02 |
0.49 |
0.10 |
|
29.00 |
2.01 |
0.48 |
0.10 |
|
29.50 |
2.00 |
0.47 |
0.09 |
|
30.00 |
1.99 |
0.47 |
0.09 |