Method for determining the amperage and the voltage of each phase of a medium voltage three-phase network coupled with a medium/low voltage transformer to a low voltage three-phase network, comprising: - the acquisition of a signal that is representative of the current (I MT_R, I MT_S, I MT_T) flowing on at least one phase of the medium voltage network and the determination of the amplitude/angle couple of the current (A I_MT_R∠ θ I_MT_R, A I_MT_S∠ θ I_MT_S, A I_MT_T∠ θ I_MT_T) on each of the phase conductors on the basis of said signals; - the acquisition of a signal that is representative of the voltage (V MT_U, V MT_V, V MT_W) on at least one phase of the medium voltage network and the determination of the angle of the voltage (θ V_MT_U, θ V_MT_V, θ V_MT_W) on each of the phase conductors on the basis of said signals; - the acquisition of a signal that is representative of the voltage (V BT_X, V BT_Y, V BT_Z) on at least one phase of the low voltage network and the determination of the amplitude/angle couple of the voltage (A V_BT_X∠ θ V_BT_X, A V_BT_Y∠ θ V_BT_Y, A V_BT_Z∠ θ V_BT_Z) on each of the phase conductors on the basis of said signals; - the calculation of the three derived amplitude/angle couples of the voltage (A V_MT_X∠ θ V_MT_X, A V_MT_Y∠ θ V_MT_Y, A V_MT_Z∠ θ V_MT_Z) for the phase conductors of the medium voltage network by modifying the three amplitude/angle couples (A V_BT_X∠θV_BT_X, A V_BT_Y∠ θ V_BT_Y, A V_BT_Z∠ θ V_BT_Z) determined on the low voltage network according to the characteristic parameters of the transformer; - the reconstruction of voltage amplitude/angle couples (A V_MT_X∠ θ V_MT_U, A V_MT_Y∠ θ V_MT_V, A V_MT_Z∠ θ V_MT_W) of the medium voltage network by substituting the angle in the derived couples (A V_MT_X∠ θ V_MT_X, A V_MT_Y∠ θ V_MT_Y, A V_MT_Z∠ θ V_MT_Z) with one of the determined respective medium voltage angles (θ V_MT_U, θ V_MT_V, θ V_MT_W) and - the pairing between these reconstructed couples and the amperage amplitude/angle couples (A I_MT_R∠ θ I_MT_R, A I_MT_S∠ θ I_MT_S, A I_MT_T∠ θ I_MT_T) for the conductors of the medium voltage network, by selecting a pair for which the three cosines of phi for each couple are greater than 0.89. - the acquisition of a signal that is representative of the current (I MT_R, I MT_S, I MT_T) flowing on at least one phase of the medium voltage network and the determination of the amplitude/angle couple of the current (A I_MT_R∠ θ I_MT_R, A I_MT_S∠ θ I_MT_S, A I_MT_T∠ θ I_MT_T) on each of the phase conductors on the basis of said signals; - the acquisition of a signal that is representative of the voltage (V MT_U, V MT_V, V MT_W) on at least one phase of the medium voltage network and the determination of the angle of the voltage (θ V_MT_U, θ V_MT_V, θ V_MT_W) on each of the phase conductors on the basis of said signals; - the acquisition of a signal that is representative of the voltage (V BT_X, V BT_Y, V BT_Z) on at least one phase of the low voltage network and the determination of the amplitude/angle couple of the voltage (A V_BT_X∠ θ V_BT_X, A V_BT_Y∠ θ V_BT_Y, A V_BT_Z∠ θ V_BT_Z) on each of the phase conductors on the basis of said signals; - the calculation of the three derived amplitude/angle couples of the voltage (A V_MT_X∠ θ V_MT_X, A V_MT_Y∠ θ V_MT_Y, A V_MT_Z∠ θ V_MT_Z) for the phase conductors of the medium voltage network by modifying the three amplitude/angle couples (A V_BT_X∠θV_BT_X, A V_BT_Y∠ θ V_BT_Y, A V_BT_Z∠ θ V_BT_Z) determined on the low voltage network according to the characteristic parameters of the transformer; - the reconstruction of voltage amplitude/angle couples (A V_MT_X∠ θ V_MT_U, A V_MT_Y∠ θ V_MT_V, A V_MT_Z∠ θ V_MT_W) of the medium voltage network by substituting the angle in the derived couples (A V_MT_X∠ θ V_MT_X, A V_MT_Y∠ θ V_MT_Y, A V_MT_Z∠ θ V_MT_Z) with one of the determined respective medium voltage angles (θ V_MT_U, θ V_MT_V, θ V_MT_W) and - the pairing between these reconstructed couples and the amperage amplitude/angle couples (A I_MT_R∠ θ I_MT_R, A I_MT_S∠ θ I_MT_S, A I_MT_T∠ θ I_MT_T) for the conductors of the medium voltage network, by selecting a pair for which the three cosines of phi for each couple are greater than 0.89.