Peter, When John Woodgate said that secondary current does not change the core flux I went back to the books to see where I went wrong. Here is what I think is going on:
The primary current that is caused by the secondary load creates a magnetic flux in the core. The secondary current creates a magnetic flux in the core. These magnetic fields are equal and opposite and therefore they cancel. Loading a transformer secondary does absolutely nothing to the magnetic core flux. The core flux is set by the magnetizing current and not the load current. Does this sound correct to the rest of the group? This has come as a revelation to me, I must say. But, it is intuitively obvious. The formulas support this but none of the papers I read pointed out why, or if they did, I missed it. Dave Cuthbert Micron Technology, Inc. From: emc-p...@ieee.org [mailto:emc-p...@ieee.org] On Behalf Of Peter Tarver Sent: Tuesday, December 20, 2005 10:43 AM To: emc-p...@ieee.org Subject: RE: What Makes a Transformer Hum in the UK? Dave - Removing the load removes flux from the core. My experience has shown that some transformers vibrate only for higher current load conditions (not necessarily at saturation) and there's negligible or no vibration with only magnetization current supporting flux in the core. Replacing the in situ load with a resistive load would demonstrate if the phenomenon John is describing is the root cause. This is more seat-of-the pants than your method but could be more direct with regard to effects load type. Regards, Peter L. Tarver, PE ptar...@ieee.org > From: drcuthb...@micron.com > Sent: Tuesday, December 20, 2005 9:01 AM > > John, > > You have helped me to think about this differently. To tell > if it is the > transformer secondary load that is the culprit one can disconnect the > load. If it still hums then the load is not the problem. > ________________________________________________________________________ _____ Scanned by Sanmina-SCI eShield ________________________________________________________________________ _____ - This message is from the IEEE Product Safety Engineering Society emc-pstc discussion list. Website: http://www.ieee-pses.org/ To post a message to the list, send your e-mail to emc-p...@ieee.org Instructions: http://listserv.ieee.org/request/user-guide.html List rules: http://www.ieee-pses.org/listrules.html For help, send mail to the list administrators: Scott Douglas emcp...@ptcnh.net Mike Cantwell mcantw...@ieee.org For policy questions, send mail to: Jim Bacher: j.bac...@ieee.org David Heald: emc-p...@daveheald.com All emc-pstc postings are archived and searchable on the web at: http://www.ieeecommunities.org/emc-pstc - This message is from the IEEE Product Safety Engineering Society emc-pstc discussion list. Website: http://www.ieee-pses.org/ To post a message to the list, send your e-mail to emc-p...@ieee.org Instructions: http://listserv.ieee.org/request/user-guide.html List rules: http://www.ieee-pses.org/listrules.html For help, send mail to the list administrators: Scott Douglas emcp...@ptcnh.net Mike Cantwell mcantw...@ieee.org For policy questions, send mail to: Jim Bacher: j.bac...@ieee.org David Heald: emc-p...@daveheald.com All emc-pstc postings are archived and searchable on the web at: http://www.ieeecommunities.org/emc-pstc
