In message <[email protected]>, dated Tue, 11 Dec 2007, "Tarver, Peter" <[email protected]> writes:
>This is a part of the ELF/VLF debate, where contention is made that HV >power lines routed near schools and housing causes increases in the >incidence of cancers and other illnesses, especially in children, or >the power lines are routed near dairy cattle effecting their milk >production. I disagree; these 'stray currents' are real. The alternating currents in the overhead conductors have mutual inductance (not much, but enough) with conducting (resistive) soil, and therefore voltage gradients are induced in the soil. Cows are astonishingly sensitive to these voltage gradients, partly because of their long 'heelbase' (sorry!), but also due to their physiology. See IEC TS60479-3. As little as 25 V r.m.s. can kill a cow, and even very low voltages can put cows under enough stress to affect milk yields and general health. > >On-premise protection devices do not come into play and grounded supply >conductors do not exist, because primary distribution is >three-phase-delta. I don't know what happens in USA, but in UK all line towers are connected together by an overhead grounded conductor at the top of each tower. To what extent this affects ground currents under normal conditions is questionable, but it does complete a big loop: tower - conductor - tower - ground ---- ground - tower. And if there is a loop, some current is bound to flow at some time. -- OOO - Own Opinions Only. Try www.jmwa.demon.co.uk and www.isce.org.uk For very important information, please turn over. John Woodgate, J M Woodgate and Associates, Rayleigh, Essex UK - 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 [email protected] 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 [email protected] Mike Cantwell [email protected] For policy questions, send mail to: Jim Bacher: [email protected] David Heald: [email protected] All emc-pstc postings are archived and searchable on the web at: http://www.ieeecommunities.org/emc-pstc
