Power theory is based on the new method of integral transformation periodic signals. Scalar inners of time vavying funcions use circuit base functions. This method can be used for decomposition of electrical quantities on active, reactive and nonactive components, unambiguos definition of circuit parameters and testinf their linearity. Presented power theory is consistent application of mathematical definitions Lebesgue´s space and Kirchhoff´s laws, while the other autors of the power theories this approach do not put in practice.