Phase Fired SCRs and Line Harmonics

Phase Fired SCRs can generate significant 3rd, 5th & 7th order harmonics above the line frequency due to the thyristor firing occurring between the AC zero crossings:

Phase Angle Control Waveform
Phase Angle Control Waveform

When Phase Fired SCRs must be used due to the load characteristics described in our previous blogs, EMI filtering can be added to the line to attenuate the harmonics.  Several companies makes suitable high current filters for Phase Fires SCRs:

http://www.filterconcepts.com/ac_filters.html

http://www.schaffnerusa.com/components-group/emi-filters.php?gclid=CIj6x_O8660CFSEQNAodoE1J6A

http://www.schurterinc.com/content/view/full/25502/(language)/eng-GB

By using the line filters with SCR Power Controls it is still possible to obtain suitable EMC performance and allow sales with a CE mark.

 
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