A device for determining the primary current of a current transformer, comprising digital processing means having a first input receiving measured instantaneous values of the secondary current of the transformer and an output supplying the instantaneous values of the associated primary current, corrected in case of saturation of the transformer, device wherein the digital processing means comprise a second input receiving a secondary voltage measured at the terminals of a secondary winding of the current transformer and connected to the input of integrating means supplying signals representative of the instantaneous magnetic flux in the secondary winding of the transformer, modelling means representative of an inverse model of the current transformer and comprising first and second inputs and an output, the first input of the modelling means being connected to the first input of the digital processing means, the second input of the modelling means being connected to the output of the integrating means and the output of the modelling means being connected to the output of the digital processing means.