Re: A challenge exploding trees

["Tesla list" <tesla-at-pupman-dot-com>]

Original poster: "Jim Lux by way of Terry Fritz <twftesla-at-qwest-dot-net>" <jimlux-at-earthlink-dot-net>



Tesla list wrote:
> 
> Original poster: "Tom Stathes by way of Terry Fritz <twftesla-at-qwest-dot-net>"
<newphreak_16-at-yahoo-dot-com>
> 
> Hello,
> 
> Noticed a mistake you made here, lightning is not RF,
> it's DC because it is an electrostatic discharge.
> This might also be why it makes the tree explode.  I
> remember seeing a 3 phase power relay once that had 2
> possible coil voltages, one was for 60hz, and the
> second was for 50hz, the 50hz voltage was lower.   As
> the frequency goes down the current has more time to
> build up, which creates more heat.


The coil is rated differently because of its inductance.  At 50 Hz, the
reactance is lower than at 60 Hz, so, with the same RMS voltage applied, it
will pass more current.  Since what makes the relay pull in is current
(and, also, that's what makes it hot), you use a different voltage for 50
and 60 Hz.

There is also a big change in inductance (and current drawn) when the core
pulls in (particularly with solenoids, where the core actually moves into
the coil). With the core in, the inductance is much higher, so the
(holding) current is lower than the actuating current.  For an AC solenoid
this means you can use smaller wire, since you can design for the holding
current (and therefore the device will be smaller, lighter, and cheaper).
Even big contactors have noticeable differences between the Pull-in current
and the holding current (partially for other reasons.. magnetic circuit
changes in the two states).

This is real noticeable on DC rated solenoid valves and such.  Big
contactors often have two separate windings, a high current one for
"pull-in" and a low current one for "holding", with some sort of
microswitch to interrupt the pull-in winding.


I don't think the RF or DC nature of the discharge is particularly
important, when it comes to blowing up trees or burning muscles.  Thermal
energy is doing the work/damage in both cases.  

> 
> --Tom
> 
> 
> --- Tesla list <tesla-at-pupman-dot-com> wrote:
> > Original poster: "Jim Lux by way of Terry Fritz
> > <twftesla-at-qwest-dot-net>" <jimlux-at-earthlink-dot-net>
> >