Explaining a Strange Phenomenon: EM Field & PC Fan

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SUMMARY

The discussion centers on the electromagnetic (EM) field generated by a PC fan powered by 220 V mains at 50 Hz, which exhibits a stable frequency of 200 Hz at a distance of three feet. This phenomenon is attributed to the motor's characteristics, potentially involving four poles, which may cause "back feeding" on the mains. The presence of even-order harmonics suggests asymmetric distortion, likely due to partial saturation of the motor's stator. The conversation also raises the possibility of nearby permanent magnets influencing the EM field.

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Ravaner
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Hello. I need an explanation for a strange phenomenon ... I use a fan (PC type) powered by mains (220 V / 50 Hz in my country). At a distance of about 3', I get a sin EM field (sure it is not by mains cords) at a stable frequency of 200 Hz synchronized on main frequency. Even during power on (acceleration) and power off. During these periods amplitude grows or decreases but frequency is sill 200 Hz. If someone can explain that, thanks by advance ...
 
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I wonder if the motor has 4 poles? Maybe that would account for the 200 Hz "back feeding" on the mains.
 
Curious. 200 Hz, being an even order harmonic would require some sort of asymmetric distortion. If the stator of the motor simply went into partial saturation on both +/- halves of the current peak, this wouldn't happen. Rectification would cause it...
Is there a permenant manget nearby?
 

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