In this paper, one-dimensional and two-dimensional calculations for the unit internal impedance of a rectangular conductor are performed, as well as expressions for the factors of increase in the working resistance, inductance and impedance due to an increase in the frequency of the current flowing through the conductor. The introductory chapter of the thesis describes its task. The second chapter introduces Maxwell’s equations of the electromagnetic field in differential form and Maxwell’s equations in the harmonic electromagnetic field and describes their form in a conductive medium. The third chapter performs a one-dimensional calculation of the unit internal impedance of a rectangular conductor, using the derived expressions for the electric and magnetic field strengths in a conductive medium, using Poynting’s theorem. Furthermore, this chapter derives expressions for the factor of increase in the working resistance, inductance and impedance due to the skin effect in a 1D calculation. The fourth chapter presents a two-dimensional calculation of the unit internal impedance of a rectangular conductor. Furthermore, this chapter derives expressions for the factor of increase in the working resistance, inductance and impedance due to the skin effect in a 2D calculation. The fifth chapter presents the replacement of a rectangular conductor with a cylindrical conductor of equivalent radius using the same circumference method and the same cross-section method. The sixth chapter presents the expression for the unit internal impedance of a cylindrical conductor. The seventh chapter presents the dependence of the increase factor of the working resistance and impedance on the frequency of the current flowing through the conductor in tabular and graphical form using selected examples. The examples presented relate to the methods of replacing a rectangular conductor with an equivalent cylindrical conductor described in the fifth chapter, and to the cylindrical conductor described in the sixth chapter.