Let us consider a primary current with a peak value _{1 p} at the CT saturation limit.

Let _{2 p} be the peak value of a primary current greater than _{1 p}, which is thus going to saturate the CT.

Let ₁ and ₂ be the peak values of the currents at the CT secondary corresponding to _{1 p} and _{2 p} through the transformation ratio. ₂ is the design value that would be obtained if there was no saturation phenomenon.

The current curves look like those in Figure C-1 (see Figure 6-5).

Figure C-1: form of current curves at the CT secondary

According to section 6.1.2, the magnetic induction B is proportional to ? I _dt.

The surface designed by the current is thus proportional to B. The current ₁ being at the saturation limit, the surface S ₁ designed by ₁ is proportional to the saturation magnetic induction.

Let us take x = ? t:

The surface S ₂ designed by the current I ₂ is:

x _s: saturation angle corresponding to the instant of saturation

The current I ₂ saturating the TC at angle x _s, the surface S ₂ saturation magnetic induction, we thus have S ₂ = S ₁.

Voltage peak value

Knowing the saturation angle, we can deduce the current peak...