I read in !emc-pstc that Robert Macy <m...@california.com> wrote (in <013301c1b033$eed45cc0$69e10...@robert.macy.california.com>) about 'Teslars???', on Thu, 7 Feb 2002: >I don't believe those numbers. We have light rail train go by here which is >powered by 600Vac (I believe it's 600 Vac) I haven't seen the fields from >the motors, only the fields from the disturbance to the earth's field >(approx 50uT) as it is being deflected by the large metal vehicles. Much >more an effect than from the power source. > >If those specs you quoted go down to 50 Hz or 60Hz, than they relate, >otherwise doubt if you'lll easily relate them. It would be "susceptibility >to AC mains magnetic fields." > >Might also look at the Swedish MPR II, or is that III now? The limit for a >monitor radiating is 200nT in this bandwidth. > >Underneath high tension wires I've seen fields around 100mG, which >translates to 10uT! and those fields are considered big. > >Again, I question those specs. Maybe they meant 0.6 to 1.7 microtesla.
The field due to traction current in overhead power conductors creates a magnetic field that can, for example, disturb CRT displays. Let us assume a distance of r = 10 m between the conductor and the display. The induction B is related to the current I by B = [mu]I/2[pi]r. [mu] is the permeability of free space, 4[pi] x 10^-7 H/m. To get 1 mT at 10 m, the current would need to be 50 000 A. This seems unlikely! Note that in some countries the traction current is not 50 or 60 Hz but 16.67 Hz. There are also still some systems using d.c. This does not affect the induction but does affect the immunity (if any!) shown by the equipment. -- Regards, John Woodgate, OOO - Own Opinions Only. http://www.jmwa.demon.co.uk After swimming across the Hellespont, I felt like a Hero. PLEASE do NOT copy news posts to me by E-MAIL! ------------------------------------------- This message is from the IEEE EMC Society Product Safety Technical Committee emc-pstc discussion list. Visit our web site at: http://www.ewh.ieee.org/soc/emcs/pstc/ To cancel your subscription, send mail to: majord...@ieee.org with the single line: unsubscribe emc-pstc For help, send mail to the list administrators: Ron Pickard: emc-p...@hypercom.com Dave Heald: davehe...@mediaone.net For policy questions, send mail to: Richard Nute: ri...@ieee.org Jim Bacher: j.bac...@ieee.org All emc-pstc postings are archived and searchable on the web at: http://ieeepstc.mindcruiser.com/ Click on "browse" and then "emc-pstc mailing list"
