In this thesis, expressions for the unit internal impedance of a cylindrical conductor and expressions for the factors of increase in working resistance, inductance and impedance due to an increase in frequency are derived. The first chapter of the thesis is introductory. The second chapter describes Maxwell’s differential equations of the electromagnetic field and Maxwell’s differential equations for the harmonic electromagnetic field. The third chapter describes the electromagnetic field in a conductive medium and the Maxwell equations that are valid in that case. The fourth chapter derives expressions for the electric and magnetic field strengths in a conductive medium and uses them to obtain expressions for the unit internal impedance of a solid cylindrical conductor, and then the impedance of a hollow cylindrical conductor. The fifth chapter presents asymptotic approximations of the Bessel and Neumann functions, which are introduced due to difficulties in numerically calculating impedance. The sixth chapter presents expressions for working resistance and inductance in direct current and uses them to obtain factors of increase in working resistance, inductance and impedance. They show how much the working resistance, inductance and impedance increase with increasing frequency. In the seventh chapter, the dependence of the working resistance, inductance and impedance increase factor on frequency is shown in tabular and graphical form using selected examples. Examples are given for copper, steel and aluminium conductors, as well as examples for conductors of different cross-sections. The difference between the increase factor of a solid and a hollow cylindrical conductor is also investigated, where it is seen that the impedance increase factor of a hollow conductor is smaller than the impedance increase factor of a solid conductor. This is especially pronounced for the protective conductive screen of a cable.