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. 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 1D calculations. The fourth chapter presents a two-dimensional calculation of the unit internal impedance of a rectangular conductor, and two different calculation methods are discussed, Rongo’s and Giacoletto’s. Furthermore, this chapter derives expressions for the increase factor of the working resistance, inductance and impedance due to the skin effect in 2D calculations. In the fifth chapter, the replacement of a rectangular conductor with a cylindrical conductor of equivalent radius using the same circumference method and the same cross-section method is presented. In the sixth chapter, the expression for the unit internal impedance of a cylindrical conductor is presented. In the seventh chapter, the dependence of the increase factor of the working resistance and impedance on the frequency of the current flowing through the conductor is presented in tabular and graphical form using selected examples. The examples presented relate to 1D and 2D calculations, and 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.