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. Equation| t [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
