View source for Harmonic distortion indicators - Crest factor

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The crest factor is the ratio between the value of the peak current or voltage(I<sub>M</sub> or U<sub>M</sub>) and its r.m.s. value.
* For a sinusoidal signal, the crest factor is therefore equal to <math>\sqrt 2</math>.
* For a non-sinusoidal signal, the crest factor can be either greater than or less than <math>\sqrt 2</math>.

The crest factor for the current drawn by non-linear loads is commonly much higher than <math>\sqrt 2</math>. It is generally between 1.5 and 2 and can even reach 5 in critical cases.

A high crest factor signals high current peaks which, when detected by protection devices, can cause nuisance tripping.


'''Examples:'''

'''Figure M7''' represents the current absorbed by a compact fluorescent lamp. 

I<sub>r.m.s.</sub> : 0.16A<br>
I<sub>M</sub> : 0.6A<br>
THD<sub>i </sub>: 145%<br>
Crest factor: 3.75
[[File:Fig_M07.jpg|none]]
'''''Fig. M7 :''''' ''Typical current waveform of a compact fluorescent lamp''


'''Figure M8''' represents the voltage supplying non-linear loads through a high impedance line, with a typical "flat top" distorted waveform.

V<sub>r.m.s.</sub> : 500V<br>
V<sub>M</sub> : 670V<br>
THD<sub>u</sub> : 6.2%<br>
Crest factor: 1.34
[[File:Fig_M08.jpg|none]]
'''''Fig. M8 :''''' ''Typical voltage waveform in case of high impedance line supplying non-linear loads''


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