  The paper discusses the relationships between electrical quantities, such as
voltages, currents, and frequency, and geometrical ones, namely curvature and
torsion. The proposed approach is based on the Frenet frame utilized in
differential geometry and provides a general framework for the definition of
the time derivative of electrical quantities in stationary as well as transient
conditions. As a byproduct, the proposed approach unifies and generalizes the
time- and phasor-domain frameworks. Other noteworthy results are a new
interpretation of the link between frequency and the time derivatives of
voltage and current; and a definition of the rate of change of frequency that
includes the novel concept of "torsional frequency." Several numerical examples
based on balanced, unbalanced, harmonically-distorted and transient voltages
illustrate the findings of the paper.
