[Amps] Re: Voodoo "EMF' forces from grid current pulses

Fri Feb 7 12:37:41 EST 2003


>When the high voltage across the room arcs, I jump too - even though there
>is no connection. Of course I jump more if I am connected.  I think if the
>arc was big enough, I would have EMF in my pants.
>
Does the F stand for feculence?
tnx

>K7FM
>
>> [Original Message]
>> From: Jeffrey Madore <K1LE at arrl.net>
>> To: AMPS <amps at contesting.com>
> > Date: 2/7/03 11:33:24 AM
>> Subject: Re: [Amps] Re: Voodoo "EMF' forces from grid current pulses
>>
>> I used to wonder if the attraction to the earth's magnetic field was a
>> plausible explanation to the jumping cables. I came to the belief that it
>is
>> not, as the earth's field is not that strong at any given location. For
>> example, I have a mag mount that is so strong that I need to use two hands
>> and considerable force to apply it to the roof of my van, lest I cause
>body
>> damage. The magnet is not noticeably attracted to earth. A magnetic
>compass
>> needle is very light yet it's reaction to the earth's field is not
>> particularly violent. In fact, it will happily point to the barrel of my
>> rifle if I'm not careful.
>> 
>> As far as shielding, enclosures, etc.  I see those as possibly enhancing
>> magnetic / mechanical forces caused by a high current pulse within the
>> shielded area. Aluminum makes a great magnet.
>> 
>> I used to do a classroom / lab demonstration where I would remove the
>rotor
>> from a 2hp 3 phase motor and place an aluminum can in the stator. Most
>> students (all adult engineering, electricians, test specialists, etc)
>would
>> guess that the stator's field would not have any effect on the aluminum
>can,
>> as it was non ferrous. I would then energize the stator and the can would
>> spin so fast that it would shoot out of the end of the stator. People were
>> then willing to understand that the aluminum bars cast within the iron of
>> the rotor, were the cause of magnetic action (through induction) and
>torque.
>> 
>> I say all that to get back to inductance and transformer theory: When an
>AC
>> current flows in a conductor (primary)  it causes a changing magnetic
>field
>> which induces a potential in anything conductive (secondary), that is
>within
>> the effects of that field.
>> 
>> If there is an electrical circuit, current will then flow in the
>secondary.
>> In the case of the aluminum can, these were circulating currents. Now, the
>> secondary current is nearly 180 degrees out of phase with the current in
>the
>> primary, thus the magnetic field produced by the secondary current is also
>> out of phase with the primary's field. This leads to maximum mechanical
>> forces.
>> 
>> So, could a large current flow between two elements within a vacuum tube,
>> cause mechanical distortion of other fragile elements within that tube? I
>> believe so.
>> 
>> 73, Jeff - K1LE - CT ><>
>> 
>> 
>> ----- Original Message -----
>> From: "Conrad G0RUZ" <conrad at g0ruz.net>
>> To: " AMPS" <amps at contesting.com>
>> Sent: Friday, February 07, 2003 6:17 AM
>> Subject: RE: [Amps] Re: Voodoo "EMF' forces from grid current pulses
>> 
>> 
>> > This can be easily explained, the welding cables are subject to the
>earths
>> > magnetic field and any other localised magnetic fields, that's why they
>> jump
>> > about. The question is, would this happen in a shielded enclosure (amp
>> > chassis) and with the magnitude of current flowing in the grid during a
>> > fault condition? I am still sceptical. One thing's for sure, something
>> > happens, but what?
>> >
>> > 73
>> >
>> > Conrad G0RUZ
>> >
>> > -----Original Message-----
>> > From: amps-bounces at contesting.com [mailto:amps-bounces at contesting.com]On
>> > Behalf Of Jeffrey Madore
>> > Sent: 07 February 2003 04:24
>> > To: 2; MorgusMagnificen at aol.com; AMPS
>> > Subject: Re: [Amps] Re: Voodoo "EMF' forces from grid current pulses
>> >
>> >
>> >
>> > >
>> > > >I strongly challenge this assertion. I know of no mechanism within
>the
>> > realm
>> > > >of classical EM field theory to account for this. I am assuming you
>are
>> > > >referring to the normal force that would accompany two
>current-carrying
>> > > >conductors which are in parallel proximity to each other.
>> > > >
>> > > Have you ever been to a welding shop and observed what happens to
>> > > arc-welder cables when an arc is struck?  I have and I saw the cables
>> > > jump about on the floor.
>> >
>> > Yea verily, Rich!
>> >
>> > In my past life I did high current trip testing on 480 volt circuit
>> > breakers. 50,000 amps was not unusual but even much lower currents would
>> > make welding cables jump off of the floor.
>> >
>> > I remember experimenting with a fairly large 480/120 3 phase lighting
>> > transformer, with a dead short on the secondary and 208 volts applied to
>> the
>> > primary via a pretty large motor control contactor and momentary push
>> > button. It was a "hit the button while peaking around the corner" type
>of
>> > experiment. We were able to draw about 2000 amps momentarily on the
>> > secondary which really made a set of welding cables jump.
>> >
>> > In my experience, a single conductor doesn't need any other conductor
>near
>> > it to display mechanical force when high current is applied. The self
>> > inductance of the cable and resulting cemf produce sufficient magnetic
>> > reaction to make the cable jump if it is not secured. Very interesting
>to
>> > look at the Z of a 4/0 welding cable...
>> >
>> > I've often found that if our engineering theories couldn't explain what
>> > appeared to take place in reality, then we needed to look deeper into
>the
>> > matter.
>> >
>> > 73, Jeff - K1LE - CT
>> >
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>> 
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>
>--- COLIN LAMB
>--- k7fm at teleport.com
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>
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-  R. L. Measures, a.k.a. Rich..., 805.386.3734, AG6K, 
www.vcnet.com/measures.  
end