Analyses of alternating electrical circuits in electrical engineering are usually based on assumption that currents and voltages are sinusoidal values. Such assumption allows analysis of electrical networks by symbolic mathematical calculation. It also allows the application of vector diagrams in representing relationship of the analyzed electrical values. In practice, periodic non sinusoidal values are sometimes found. For solving such values symbolic mathematical calculation and vector diagrams cannot be used. In this paper is shown how such non sinusoidal periodic values can be separated, by applying Fourier series, into infinite series which contains a constant term and infinitely many harmonic components. That way allows all the acquired knowledge and methods for solving sinusoidal periodic values to still be used.