The operate times for the standard undervoltage IDMT curves are defined with the coefficients A, B, C, D and E.
The inverse operate time can be calculated with the formula:
Figure 1. Equationt [s] | Operate time in seconds |
U | Measured voltage |
U< | Set value of the Start value setting |
k | Set value of the Time multiplier setting |
Table 1. Curve coefficients for standard undervoltage IDMT curves
Curve name |
A |
B |
C |
D |
E |
(21) Inverse Curve A |
1 |
1 |
0 |
0 |
1 |
(22) Inverse Curve B |
480 |
32 |
0.5 |
0.055 |
2 |
Figure 2. : Inverse curve A characteristic of undervoltage protection
Figure 3. Inverse curve B characteristic of undervoltage protection