ICP-S Technical Manual
Overcurrent Protection Elements
Rev.A
6/13
6. I
2
t Calculation of a Variety of Wave forms
If the steady-state current includes a pulse, surge, or inrush current, calculate the I
2
t of
the wave form of the current. The following graphs and formulas show how to calculate
a variety of wave forms.
• The charged wave form is segmented as shown below. The Joule heat
generated during each segmented period is plotted onto a Joule integral
sheet.
1) Triangular
wave form
0
t
Im
I
2
t = Im
2
t
3
1
2) Rectangular
wave form
I
2
t = Im
2
t
0
t
Im
3) Irregular
wave form
4) Charged or
discharged
wave form
0
t
I1
I2
I
2
t = I
1
I
2
t + (I
1
−
I
2
)
2
t
3
1
1
2
3
4
5
Segments 1 through 4 are treated as
irregular wave forms and calculated,
while segment 5 is treated as a
triangular wave form and calculated.
