The operate times for the standard overvoltage 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 Start value
k
Set value of Time multiplier
Table 1. Curve coefficients for the standard overvoltage IDMT curves
Curve name
A
B
C
D
E
(17) Inverse Curve A
1
1
0
0
1
(18) Inverse Curve B
480
32
0.5
0.035
2
(19) Inverse Curve C
480
32
0.5
0.035
3
Figure 2. Inverse curve A characteristic of overvoltage protectionFigure 3. Inverse curve B characteristic of overvoltage protectionFigure 4. Inverse curve C characteristic of overvoltage protection