Harmonic distortion indicators - Crest factor
From Electrical Installation Guide
Definition
The crest factor is the ratio between the value of the peak current or voltage (Im or Um) and its rms value.
- For a sinusoidal signal, the crest factor is therefore equal to [math]\displaystyle{ \sqrt 2 }[/math].
- For a non-sinusoidal signal, the crest factor can be either greater than or less than [math]\displaystyle{ \sqrt2 }[/math].
In the latter case, the crest factor signals divergent peak values with respect to the RMS value.
Interpretation of the crest factor
The typical crest factor for the current drawn by non-linear loads is much higher than [math]\displaystyle{ \sqrt2 }[/math] It is generally between 1.5 and 2 and can even reach 5 in critical cases. A high crest factor signals high transient overcurrents which, when detected by protection devices, can cause nuisance tripping.
