# Electrical frequency

The electrical frequency is the fundamental frequency of the current and voltage at the machine terminals measured in [Hz].

The electrical frequency can be calculated as the mechanical speed multiplied by the number of pole pairs $p/2$. Assuming a mechanical speed $n$ of 1500rpm (corresponding to 25 1/s) and a 4-pole machine, the electrical frequency of a synchronous machine can be calculated as: $$f=n\frac{p}{2}=50\: \mathrm{Hz}$$

In an asynchronous machine, there is a difference between the speed of the rotating field produced by the stator windings and the mechanical speed, called slip. Assuming a slip $s$ of 5%, the electrical frequency can be calculated as: $$f=\frac{n}{(1-s)}\frac{p}{2} =52.6\: \mathrm{Hz}$$