CT Saturation Check

Verify a protection current transformer against the 10% error (accuracy-limit) requirement: required knee-point voltage versus the actual knee-point voltage, plus available accuracy-limit factor and saturation ratio (IEC 60044-1 / IEEE C57.13 simplified).

Inputs

Fault primary current Iₚ A

CT ratio —

Rated secondary Iₛₙ A

Required ALF ×

Winding R_ct Ω

Actual burden R_b Ω

Lead R_w Ω

Actual knee-point V_k V

Results

Note — The required knee-point voltage uses Vk = ALF·Iₛₙ·(R_ct + R_b + R_w). The check passes when the actual Vk ≥ required Vk (equivalently saturation ratio V_ex/V_k ≤ 1). It is a steady-state reactance-free approximation; confirm the full excitation characteristic and the relay burden against the CT type test and a certified engineer.